2024-03-29T09:53:45Zhttps://research-repository.st-andrews.ac.uk/oai/requestoai:research-repository.st-andrews.ac.uk:10023/149462019-04-01T10:02:25Zcom_10023_126com_10023_31col_10023_129
Sibbett, Wilson
McGowan, Cathrine
Engineering and Physical Sciences Research Council (EPSRC)
227 p.
2018-07-05T08:16:22Z
2018-07-05T08:16:22Z
1998-02
http://hdl.handle.net/10023/14946
The research presented in this thesis is concerned with the generation and characterisation of femtosecond pulses in the near and mid-infrared spectral regions. The three optical parametric oscillators which were constructed were synchronously- pumped by a self-modelocked femtosecond Ti:sapphire laser. Noncollinear critical birefringent phasematching was used in an oscillator based on KTiOAsO4, which was tunable from 1.03 to 1.2 mum and 2.51 to 4.1 mum by varying the crystal angle. The mid-infrared pulses were sub-100 fs, and essentially free from frequency chirp. With appropriate dispersion compensation the near-infrared signal pulses were temporally compressed to 69 fs. Theoretical models of noncollinear phasematching were derived and the results agreed closely with experiment. A novel optical parametric oscillator design based on a semi-monolithic noncritically phasematched RbTiOAsO4 crystal was implemented. This unique cavity configuration allowed independent focussing of the pump and signal beams within the crystal. It facilitated a reduction in cavity length to bring the signal pulse repetition rate into synchronism with the second (172 MHz) and fourth (344 MHz) harmonics of the pump pulse repetition frequency. Extraction efficiencies as high as 55% were observed. Quasi-phasematched femtosecond optical parametric oscillation was demonstrated in periodically poled lithium niobate. This device offered extensive tunability, covering 0.975 to 1.54 mum in the signal branch and 1.67 to 4.55 mum in the idler branch, from a combination of grating, pump wavelength and cavity length tuning. A theoretical model indicated that a very broad gain bandwidth allowed the wide tuning range. An attractively low oscillation threshold of 45 mW was recorded, and a visible output of 70 mW at 540 nm was observed, caused by simultaneously phasematched frequency-doubling of the signal output. The pulses from the Ti:sapphire laser and from the optical parametric oscillators were characterised by autocorrelation and frequency-resolved optical gating techniques. A highly advantageous autocorrelator arrangement based on quadratic nonlinearity in light-emitting diodes and photodiodes was demonstrated, and a novel second harmonic generation frequency-resolved optical gating system allowed real-time monitoring of pulsed outputs and complete characterisation of the intensity and phase of pulses.
en
University of St Andrews
The University of St Andrews
TK7872.O7M5
Oscillators
Optical parametric oscillators
Femtosecond optical parametric oscillators for the mid-infrared
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/156912019-07-25T08:38:39Zcom_10023_126com_10023_31col_10023_129
Turnbull, Graham A.
Stevenson, James Robert Young
270 p.
2018-07-24T14:05:23Z
2018-07-24T14:05:23Z
2016
http://hdl.handle.net/10023/15691
en
University of St Andrews
The University of St Andrews
QD382.S4S8
Title redacted
Thesis
Doctoral
PhD Doctor of Philosophy
2018-04-30
Thesis restricted in accordance with University regulations. Electronic copy restricted until 30th April 2018
oai:research-repository.st-andrews.ac.uk:10023/146912019-04-01T10:02:27Zcom_10023_126com_10023_31col_10023_129
ter Haar, D.
Ross, Archie Walter
Department of Scientific and Industrial Research (DSIR)
126 p.
2018-06-28T09:33:48Z
2018-06-28T09:33:48Z
1957
http://hdl.handle.net/10023/14691
en
University of St Andrews
The University of St Andrews
QC761.R7
Magnetism
The effect of volume changes on the order-disorder transition in substitutional alloys
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/120482018-07-24T10:42:14Zcom_10023_126com_10023_31col_10023_129
Wahl, Peter
Aluru, Rama K. P.
University of St Andrews. St Leonard's College
University of St Andrews. 600th Anniversary Scholarship
xxxvi, 165 p.
2017-11-10T12:17:27Z
2017-11-10T12:17:27Z
2017-12-07
http://hdl.handle.net/10023/12048
The discovery of high-temperature superconductivity in 1986 in copper-oxide materials have
opened up new avenues to investigate new families of quantum materials that were previously
not known. Understanding the mechanism of superconductivity in high-T[sub]c superconductors
has been an important research theme in condensed matter physics, as it is believed to be
essential to realize the next generation engineered materials that become superconducting at
room temperature. Discovered in 2006, iron based superconductors are a new addition to
the family of high-T[sub]c superconductors, these materials exhibit several interesting properties
and show some vivid similarities with cuprates and other families of high-temperature
superconductors.
In this thesis, I will present the spin-polarized scanning tunneling microscopy (SPSTM) study carried out on the parent compound of iron chalcogenide high temperature superconductor Fe[sub](1+y)Te to investigate the bi-collinear antiferromagnetic order. Magnetic tips in this work are prepared using a novel preparation technique by picking up excess iron atoms and clusters of FeTe from the surface of the sample. Next, I will present the SP-STM results obtained in the spin glass phase of Fe[sub](1+y)SeₓTe₁₋ₓ visualizing the interplay between the short ranged bi-directional bi-collinear antiferromagnetic order and superconductivity at the atomic scale.
In this thesis, I will also present the scanning tunneling microscopy and spectroscopy (STM/STS) study of the native and engineered defect bound states in the iron-pnictide superconductor LiFeAs. This study addresses the pairing symmetry of the superconducting order parameter and understanding of dip-hump features seen in STM spectra outside the superconducting gap in iron pnictide superconductor LiFeAs.
en
University of St Andrews
The University of St Andrews
Iron based superconductors
Scanning tunnelling microscopy
Spin polarized STM
High temperature superconductors
Iron chalcogenides
LiFeAs inelastic tunnelling
QC611.98I76A6
High temperature superconductors--Magnetic properties
Iron-based superconductors
Spectroscopic imaging STM study of the interplay between magnetism and superconductivity in iron-based superconductors
Thesis
Doctoral
PhD Doctor of Philosophy
2019-10-26
Thesis restricted in accordance with University regulations. Print and electronic copy restricted until 26th October 2019
oai:research-repository.st-andrews.ac.uk:10023/219022022-01-07T09:25:46Zcom_10023_126com_10023_31col_10023_129
Stradling, R. A.
Thorley, Antony M.
178p
2021-04-08T08:59:19Z
2021-04-08T08:59:19Z
1990
http://hdl.handle.net/10023/21902
A theoretical and experimental investigation of the optical properties of ion-implanted silicon over the wavelength range 2 μm to 3 cm has been performed. Twelve samples were supplied by Hughes Microelectronics Ltd. and a further two from Plessey Research Caswell. In the near infrared (short wavelength region) plasma edge features are seen for implants of 10¹⁵ions / cm² and above. The feature shape is sensitive to the donor implant distribution and this allows contactless characterisation through the use of a computer model developed in chapters 1 and 2. In the far infrared interference fringes are seen with modulation close to theory and the total transmission is sensitive to implant dose. Millimeter quasi optical results are in close agreement with the theory. The near infrared is limited to doses of 10¹⁵ions / cm² and above for implant distribution measurements, whilst at centimeter wavelengths a 4 x difference between the transmission at 10¹⁵ions / cm² and zero dose should allow an implant as low as 2x10¹⁴/cm² to be identified. At centimeter wavelengths the absolute fit between theory and experiment is not as good as in the millimeter and shorter wavelengths due to standing waves in the experimental arrangement. The possibility exists for tuning out these reflections with matching stubs and, with appropiate modeling, achieving even higher sensitivity in transmission to implant doses below 2x10¹⁴/cm². Level crossing effects in Zeeman split donor states in GaAs were investigated. Ho conclusive evidence for these was found within the limits of sensitivity of the experiments indicating that any amplitude is below 10% of the main transition intensity.
en
University of St Andrews
The University of St Andrews
QC611.6O6T7
Semiconductors--Optical properties
Semiconductors--Research
Silicon--Optical properties
Infrared characterisation of semiconductors
Thesis
Doctoral
PhD Doctor of Philosopy
oai:research-repository.st-andrews.ac.uk:10023/143932019-04-01T10:02:28Zcom_10023_126com_10023_31col_10023_129
Kilkenny, David
131 p.
2018-06-21T11:49:02Z
2018-06-21T11:49:02Z
1973
http://hdl.handle.net/10023/14393
A survey of early-type stars at intermediate galactic latitudes was carried out in the southern hemisphere winters of 1970 and 1971. The observing programme was limited to negative declinations and covered a range in right ascension of approximately 12ʰ to 20ʰ. At the Royal Observatory, Cape Town, in 1970, UBV photoelectric measurements were made of 56 stars for which no UBV data existed and 20 stars which had been observed on one or two previous occasions, the intention being to obtain four separate measures of each star. In 19711 the Bochum University telescope at the E.S.O. site in Chile was used for H/3 photoelectric photometry of over 200 intermediate and high latitude stars. Shortly afterwards, spectra for radial velocity determination and MK classification were obtained with the two-prism spectrograph and 74" reflector of Radcliffe Observatory, Pretoria. Work was concentrated upon some 60 stars not previously observed with spectroscopic equipment and selected on the basis of blue colour or possible high luminosity from photometric considerations. A few southern standard stars and stars from earlier Radcliffe programmes were re-observed as control or overlap stars. Chapters II - IV describe the observational procedures and reduction methods. Tables in chapter V contain results from the 1970-71 programmes plus UBV and spectroscopic data for intermediate and high latitude stars from various other sources. The remaining chapters are concerned with analysis and discussion of the observations. Chapter VI summarises some optical and radio determinations of the spiral structure of the Galaxy and compares the spatial distribution of the programme stars with these results. The possibility that early-type stars may be formed well away from the galactic plane is considered by comparison of kinematic and evolutionary lifetimes of some stars at appreciable distances from the plane. In chapter VII, intermediate and high latitude stars are shown to participate in the differential rotation of the Galaxy and detailed analysis of the space motions of a number of high velocity stars leads to the conclusion that some may .have sufficient energy to escape from the galactic system. The radial velocities of interstellar Ca II lines are shown in chapter VIII to be as expected for material in the solar neighbourhood involved in differential galactic rotation. An apparent deviation from circular motion reported by observers investigating H II regions is also present in the Ca II gas. Constants in the cosecant equation of interstellar reddening are re-determined and show an apparently significant difference between northern and southern galactic hemispheres. Appendix I describes attempts to simulate the effect of filters in order to explain the curvature in the transformations from instrumental to standard photometric systems. Appendix II gives details of the method used to compute stellar space velocities from proper motions and radial velocities and includes a short Fortran IV programme which implements the operations described.
en
University of St Andrews
The University of St Andrews
QB843.B8
Early stars
Southern hemisphere early-type stars at intermediate and high galactic latitudes
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/148862018-07-26T09:23:12Zcom_10023_126com_10023_31col_10023_129
Sibbett, Malcolm H.
Gibson, Graham Martin
Engineering and Physical Sciences Research Council (EPSRC)
185 p.
2018-07-04T08:48:44Z
2018-07-04T08:48:44Z
1999-05
http://hdl.handle.net/10023/14886
Within the past few years, renewed interest has been generated in the field of continuous wave optical parametric oscillators. This has been due in part, to the wider range of nonlinear materials now available, and also to the improvements being made in the pump sources for these devices. OPO resonator design has also been stimulated and the use of monolithic / semi-monolithic cavities which display high levels of passive stability has been realised. The work to be described herein was prompted by a desire to develop a doubly resonant optical parametric oscillator with frequency stable, high integer ratio signal-idler tunable outputs pumped in the green spectral region. Given a pump source constrained to be in the green spectral region, the nonlinear material of choice for the optical parametric oscillator (OPO) was lithium triborate (LBO). The target device for this work was a tunable, type I LBO doubly resonant oscillator (DRO) with a signal: idler frequency output ratio of 3 : 1. This configuration necessitates a high operating temperature which, it was predicted, would lead to problems with the nonlinear OPO crystal coatings. LBO, as will be discussed later, suffers from an anisotropic thermal expansion which leads it to expand on heating in two crystal directions but to contract in the third crystal direction. This has in the past led to problems with the dielectric coatings applied to the surfaces of the crystal whereby the coatings and the crystal become separated upon temperature cycling. The solution to this problem developed within this thesis, involves the use of index-matching fluid to attach cavity mirrors directly onto the faces of the nonlinear material. The cavity mirrors, constructed from a substrate which exhibits an isotropic thermal expansion, could then be dielectrically coated and temperature cycled successfully. The index-matching fluid would provide the contact necessary to maintain high finesse optical cavities. The first device to be built in this way was a type EL, LBO DRO which operated successfully with signal and idler output wavelengths of 946 and 1126 nm respectively. Other devices were also investigated during this time, including the target device, and they are discussed later within this thesis. However, the first device developed displayed frequency stability characteristics far in excess of what had been expected theoretically and a thermal feedback mechanism was proposed to explain its behaviour. This device was presented at The Conference on Lasers and Electro-Optics (C.L.E.O.) in 1995 and a discussion with a fellow delegate brought to my attention an independent proposal of a similar thermal feedback mechanism used to explain the enhanced frequency stability within other parametric devices. A period of work was then undertaken to prove the existence of this mechanism and to characterise it fully. The thermal feedback mechanism was subsequently computer modelled successfully and a solid-state laser was designed and built in order to probe this mechanism experimentally. Whilst technical problems were encountered which prevented a full characterisation of the said mechanism, evidence for it was found in the micro-operating characteristics of such a solid-state laser pumped, type II, pseudo-monolithic DRO.
en
University of St Andrews
The University of St Andrews
Continuously frequency-tunable CW optical parametric oscillators and their application to spectroscopy
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/35582019-07-01T10:05:43Zcom_10023_126com_10023_31col_10023_129
Dunn, Malcolm H.
Lerski, Richard
Houston, Graeme
Matthew, Shona
260
2013-05-27T13:09:39Z
2013-05-27T13:09:39Z
2012-11-30
http://hdl.handle.net/10023/3558
Cardiovascular disease (CVD) is a term used to describe a variety of diseases and events that impact the heart and circulatory system. CVD is the United Kingdom’s (UKs) biggest killer, causing more than 50,000 premature deaths each year. Early recognition of the potential for magnetic resonance imaging (MRI) to provide a versatile, non-ionising, non-invasive, technique for the assessment of CVD resulted in the modality becoming an area of intense interest in the research, radiology and cardiology communities. The first half of this thesis reviews some of the key developments in magnetic resonance hardware and software that have led to cardiac magnetic resonance imaging (CMRI) emerging as a reliable and reproducible tool, with a range of applications ideally suited for the evaluation of cardiac morphology, function, viability, valvular disease, perfusion, and congenital cardiomyopathies. In addition to this, the advantages and challenges of imaging at 3.0T in comparison to 1.5T are discussed. The second half of this thesis presents a number of investigations that were specifically designed to explore the capability of CMRI to accurately detect subtle age and disease related changes in the human heart. Our investigations begin with a study at 1.5T that explores the clinical and scientific significance of the less frequently used measure of right ventricular function to test the hypothesis that the inclusion of this data provides a more informative assessment of overall cardiac function. The focus then shifts to imaging at 3.0T and the challenges of optimising cardiac imaging at this field strength are discussed. Normal quantitative parameters of cardiac function are established at this field strength for the left ventricle and the left atrium of local volunteers. These values are used to investigate disease related changes in left ventricle and left atrium of distinct patient cohorts. This work concludes by investigating the impact of gadolinium-based contrast agents on the quantitative parameters of cardiac function.
en
University of St Andrews
The University of St Andrews
University of Dundee
Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported
http://creativecommons.org/licenses/by-nc-nd/3.0/
Cardiac
Magnetic resonance
RC670.5M33M2
Cardiovascular disease diagnostic equipment industry--Technological innovations
Cardiovascular system--Diseases--Magnetic resonance imaging
The development and assessment of cardiac magnetic resonance imaging for the detection of age- and disease-related changes in the human heart
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/20662019-07-01T10:06:37Zcom_10023_126com_10023_31col_10023_129
Samuel, Ifor D. W.
Levell, Jack William
193
2011-11-24T12:37:38Z
2011-11-24T12:37:38Z
2011-11-30
http://hdl.handle.net/10023/2066
This thesis describes investigations into the photophysical properties of luminescent
materials and their application in optoelectronic devices such as light emitting diodes
and photodetectors. The materials used were all solution processable because of the
interest in low cost processing of organics.
I have investigated the photophysics of 1,4,5,8,9,12-hexamethyltriphenylene, a
triphenylene derivative which has its luminescence enhanced by the addition of
methyl groups. These groups change the planar shape of the triphenylene molecule
into a twisted one, changing the symmetry of the molecule and increasing its dipole
moment in absorption and emission by ~4 fold. This increased its rate of radiative deexcitation
by ~20 times. In addition, the twisted shape of the molecule prevents
intermolecular interactions and concentration effects from affecting the luminescence.
This results in an efficient solid-state photoluminescence quantum yield of 31%.
This thesis also includes an investigation into phosphorescent polymer dendrimers,
designed to have suitable viscosities in solution for inkjet printed OLED applications.
A photophysical study of the intra-chain aggregation effects on the luminescence was
undertaken in both homopolymers and copolymers with high energy gap spacer units.
Using double dendrons to increase the steric protection of the luminescent cores, the
best homopolymers achieved 12.1% external quantum efficiency (39.3 cd/A) at 100
cd/m² brightness and the best co-polymer achieved 14.7% EQE (48.3 cd/A) at 100
cd/m². This compares favourably with 11.8% EQE for the best phosphorescent
polymer and 16% for the best solution processed dendrimer OLED previously
reported.
Finally I have applied a solution processed enhancement layer to silicon photodiodes
to enhance their ultraviolet response. Using a blend of materials to give favourable
absorption and emission properties, 61% external quantum efficiency was achieved at
200 nm, which is better than the 20-30% typical for vacuum deposited lumogen
enhancement layers used commercially.
en
University of St Andrews
The University of St Andrews
Creative Commons Attribution-NoDerivs 3.0 Unported
http://creativecommons.org/licenses/by-nd/3.0/
Photophysics
Iridium complex
Polymer
Photodiode
Luminescence
Phosphorescent
OLED
TK8304.L4
Optoelectronic devices--Design and construction
Organic compounds--Optical properties
Optical materials
Photodiodes
Material and device design for organic optoelectronics
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/218022021-10-21T02:00:44Zcom_10023_126com_10023_31col_10023_129
Cywinski, Bob
Hillier, Adrian
Physics & Astronomy Theses
204p
2021-04-08T08:45:32Z
2021-04-08T08:45:32Z
1999
http://hdl.handle.net/10023/21802
The problem of finding an appropriate classification scheme for the remarkably diverse range of known superconducting materials is a long standing one. Nevertheless the literature abounds with claims of discoveries of "new classes" of superconductors, although the nature of the "class" is rarely defined explicitly. In cases where the structural, electronic or magnetic properties of the new superconductor are particularly unusual it is tempting to accept such claims: heavy fermions, high Tc cuprates, organic superconductors and buckminsterfullerenes are all examples of superconducting materials which superficially have little in common either with each other or with the more conventional superconducting elements and compounds and might therefore be considered as genuinely belonging to different classes. However the underlying uniformity of the superconducting ground state and its general conformity with the predictions of BCS theory continues to unite an extraordinarily disparate group of superconducting materials. Consequently over the last few decades there have been numerous attempts to provide an empirical framework, based upon the fundamental parameters of the superconducting state, within which superconducting materials can be compared and contrasted, thus enabling classes of superconductor to be unambiguously identified. For example, until the early 1980s a correlation between the superconducting transition temperature, Tc, and the Sommerfeld constant, i.e. the coefficient of the linear electronic specific heat 𝛶, was frequently invoked. A plot of logTc versus log 𝛶 was found to yield an approximately universal curve (see figure 1.1) ¹. However, first the heavy fermion compounds, with enormous 𝛶 s yet low transition temperatures and then, later, the cuprates with modest 𝛶 s but remarkably high Tcs proved to be marked exceptions to this universality, apparently confirming their status as members of new, exotic classes of superconductors.
More recently a rather surprising universal scaling relationship has emerged from systematic transverse field muon spin rotation (μSR) measurements of flux penetration in superconducting systems. Uemura and co-workers ² were the first to recognise the new scaling relationship, observing that for several different members of the family of high temperature cuprate superconductors an initial increase in carrier doping leads to precisely the same linear increase of Tc with the muon spin depolarisation rate, σ. Deviations from linearity, first appearing as a saturation and then a suppression of Tc, only appears at high levels of doping. Remarkably, several Chevrel phase superconductors were also found to follow the same linear relationship, while bismuthates, fullerenes, organic superconductors and heavy fermion compounds exhibit a similar scaling behaviour3,4.
The correlation between Tc and σ observed in μSR studies has suggested a new empirical framework for classifying superconducting materials. In this thesis I shall briefly review the role played by μSR in establishing this new classification scheme, and discuss the underlying physical phenomena responsible for the observed correlations. I shall present some μSR measurements on a range of superconducting families and attempt to interpret the results of these measurements within the proposed classification scheme.
en
University of St Andrews
The University of St Andrews
QC612.S8H5
Superconductors
A μSR study of unconventional superconductors
Thesis
Doctoral
PhD Doctor of Philosopy
oai:research-repository.st-andrews.ac.uk:10023/113632019-04-01T10:02:29Zcom_10023_126com_10023_31col_10023_129
Helling, Christiane
Rodriguez-Barrera, Maria Isabel
vii, 98 leaves
2017-08-03T12:53:59Z
2017-08-03T12:53:59Z
2017
http://hdl.handle.net/10023/11363
Recent observations of ultra-cool objects suggest that the gas in their uppermost atmospheres is heated, ionised and magnetised to levels that radio and X-ray emission is possible. The aim
of this work is to identify which low mass objects are most susceptible to plasma and magnetic
processes by the effect of thermal ionisation and Lyman continuum photoionisation from the
irradiation of external sources in different environments. I focus my work on very low mass,
ultra-cool objects (late M-dwarfs, brown dwarfs and giant gas planets: T[sub]eff = 1000 . . . 3000 K)
to analyse the electrostatic and magnetic character of these atmosphere. This work has been
carried out in two distinct parts:
a) A reference study to identify which ultra-cool objects are most susceptible to plasma and
magnetic processes considering the thermal ionisation as the only mechanism to ionise
the atmospheric gas. This presents a theoretical framework using a set of fundamental
parameters to analyse the ionisation and magnetic coupling state of objects with
ultra-cool atmospheres. The DRIFT-PHOENIX model atmosphere simulations are used to
determine the local gas properties T[sub]gas [K], p[sub]gas [bar], pₑ [bar] of the atmospheres
structures from the global parameters T[sub]eff [K], log(g) [cm s⁻²] and [M/H]. Electrostatics
interactions dominance over electron-neutral interactions increases as T[sub]eff increases:
throughout the M-dwarf atmospheres, almost for the whole brown dwarf atmospheres
and only giant gas planets with T[sub]eff =1200 K, log(g)=3.0, [M/H]=+0.3 fulfil that criterion
at the most deeper atmosphere. A magnetised gas is found for M-dwarfs, brown
dwarfs and giant gas planet atmospheres even for those with a small degree of ionisation
except to the most deeper atmospheric regions. Hence, the upper atmosphere of
all of studied objects can be magnetically coupled. A large fraction of the atmospheric
volume of M-dwarfs and of early spectral subtypes of brown dwarfs is found to occur
plasma processes and magnetised gas, and are therefore the best candidates to emit in
Hα and radio wavelengths.
b) An analysis of how the Lyman continuum external irradiation effect the plasma and magnetic
state of an ultra-cool atmospheres in additional thermal ionisation. The Monte
Carlo radiative transfer code simulations provide the atmospheric ionisation structure
due to photoionisation. Three different cases are studied to see the effect of the Lyman
continuum irradiation given by an external source: free-floating ultra-cool objects
irradiated by Lyman continuum photons from the interstellar medium (dominated by
Galactic O and B stars), brown dwarfs in star forming regions irradiated by a nearby
(few parsecs) O star and binary systems where a brown dwarf atmosphere is photoionised
by a companion white dwarf. The effect of Lyman continuum irradiation from
external sources greatly increases the level of ionisation in the uppermost atmospheric
regions. Brown dwarfs in star forming regions and brown dwarfs in binary systems with
a companion white dwarf have upper atmospheres that are close to being fully ionised.
Adopting temperatures typical for a chromosphere or a corona, the resulting free-free
X-ray luminosities are found to be comparable with those observed from brown dwarfs
in star forming regions. The results of this study show that it is not unreasonable to
expect powerful energy emissions from brown dwarf atmospheres.
The conclusions of this study are that the thermal ionisation allows the establishment of a magnetised plasma in brown dwarf atmospheres as in particular the rarefied upper parts of the atmospheres despite having low degrees of thermal gas ionisation and that the Lyman continuum photoionisation allows to argue for a chromosphere/corona on brown dwarfs and for X-ray emissions from ultra-cool objects. However, other mechanisms, like Alfvén wave heating, are needed to occur which then lead to rise the local gas temperature in the chromosphere/corona on brown dwarfs.
en
University of St Andrews
The University of St Andrews
QB820.R7
Brown dwarf stars--Atmospheres
Outer planets--Atmospheres
Ionization of gases
Ionization in atmospheres of brown dwarfs and giant gas planets
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/285732023-10-27T02:00:42Zcom_10023_126com_10023_31col_10023_129
Samuel, Ifor D. W.
Zysman-Colman, Eli
Diesing, Stefan
University of St Andrews. St Leonard's College
Engineering and Physical Sciences Research Council (EPSRC)
xxii, [175] p.
2023-10-26T08:11:10Z
2023-10-26T08:11:10Z
2023-11-29
http://hdl.handle.net/10023/28573
https://doi.org/10.17630/sta/635
EP/R513337/1
Efficient organic light-emitting diodes (OLEDs) enable the commercialisation of energy efficient and high contrast displays, and are being exploited increasingly in telecommunication and biomedical applications. In an efficient OLED all electrically generated singlet and triplet excitons recombine to emit light. In recent years, the exploitation of emitters that show thermally activated delayed fluorescence (TADF) has proven to be a complementary strategy to phosphors that leads to devices of comparable efficiencies without relying on scarce metals in the emitter design.
In this thesis, the kinetics of TADF are explored. First, two families of novel emitters are discussed by investigating their photophysics. One series incorporates a novel pyridazine acceptor whilst the other series makes use of a through-space conjugated donor design using a [2,2]paracyclophane. In both families of emitters, the emitter with the largest donor strength showed efficient triplet up-conversion via TADF in OLEDs.
The kinetics of TADF can be calculated from a bimolecular fit of the transient photo- luminescence (PL). However, in the literature, different assumptions are used to calculate rate constants from these data. Therefore, a three-level model was analysed to understand the limiting cases employed in literature.
The transient PL of TADF is characterised by two decay regimes that stretch over multiple orders of magnitude in time and intensity. This makes recording both regimes in one measurement challenging. To solve this, first improvements and implementations of existing techniques are discussed. In order to remove the need to measure over a large dynamic range of intensities a novel measurement technique was developed which allows the extraction of kinetic parameters of TADF by recording the emission during a step-function excitation.
Finally, a figure of merit based on the TADF kinetics under constant electrical excitation was developed to evaluate new TADF emitters for use in OLED with low efficiency roll-off.
en
Measurements and Modelling of the Kinetics of Thermally Activated Delayed Fluorescence (thesis data)
Diesing, S., University of St Andrews, 9 Oct 2024. DOI: https://doi.org/10.17630/5a006c14-47f8-4309-81ab-ddc2fd25191f
https://doi.org/10.17630/5a006c14-47f8-4309-81ab-ddc2fd25191f
TADF
OLED
Thermally activated delayed fluorescence
Organic light-emitting diodes
Kinetics
Photophysics
TK7871.89L53D5
Light emitting diodes
Fluorescence
Measurements and modelling of the kinetics of thermally activated delayed fluorescence
Thesis
Doctoral
PhD Doctor of Philosophy
The University of St Andrews
2024-10-09
Thesis restricted in accordance with University regulations. Restricted until 9th October 2024
oai:research-repository.st-andrews.ac.uk:10023/206652021-01-25T15:35:04Zcom_10023_126com_10023_31col_10023_129
O’Faolain, Liam
Hu, Changyu
158 p.
2020-09-22T13:18:13Z
2020-09-22T13:18:13Z
2020-12-01
http://hdl.handle.net/10023/20665
https://doi.org/10.17630/10023-20665
Nowadays, information technology has been deeply integrated in our daily life. However, within its rapid development, it faces a serious bottleneck due to the prohibitive power consumption and limited transmission bandwidth of electrical interconnects. Silicon photonics introduces a potential solution for information technology based on optical communication. In this field, delay-bandwidth devices offer a high bandwidth optical interconnection and low power consumption for the next generation information communication technology. Through introducing the slow light effect, I can realise time domain control and store the light to achieve a new functional component, which is the optical buffer for optical information processing. The optical buffer allows us to control and store the light, using as the optical information process and transit. However, the current optical buffer devices are limited by high optical loss and the ability to produced tunable group delay of the light. In this thesis, I examine different configurations of the coupled photonic crystal resonator system and then introduce a novel tuneable delay line, based on photonic crystal cavity structures. Through the optical analog to electromagnetically induced transparency (EIT), an EIT-like transmission spectrum has been achieved in coupled photonic crystal cavities. By tuning the phase difference between two coupled resonators and resonance wavelength, I can achieve the desired analog conditions and reach to a maximum group delay of 360 ps. By adding thermal tuning pattern, I have demonstrated a tuning of the group delay of over 120 ps range at a low input power and a maximum delay of 300 ps group delay in coupled photonic crystal cavities system. All devices are with a footprint at only 200 μm², and with integrated compatibles as well. By employing a new vertical coupling technique, a record low loss 15 dB/ns is presented making this system very promising for practical optical information applications.
en
University of St Andrews
The University of St Andrews
Photonic crystal
Electromagnetically induced transparency
Coupled cavities system
TA1660.H7
Photonic crystals
Transparency
Cavity resonators
Optical interconnects
Photonic crystal cavity based optical induced transparency
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/140372019-04-01T10:02:30Zcom_10023_126com_10023_31col_10023_129
Maitland, Arthur
Condon, Brian P.
158p, 11p of plates.
2018-06-14T08:46:49Z
2018-06-14T08:46:49Z
1993-07
http://hdl.handle.net/10023/14037
We propose to alter the propagation conditions experienced by a microwave beam by the generation of a "laser beam atmospheric waveguide". The waveguide is formed by tailored refractive index changes caused by the absorption of a small part of the energy of an annular laser beam. The objective is to increase the microwave radiation field experienced by a target through improved directionality rather than total radiated power from the source. The equations governing the propagation of high power laser beams in the paraxial limit and their interactions (both linear and non-linear) with an absorbing atmosphere are derived and studied. The mechanisms which lead to the formation of the guide and the effects of the propagation environment are considered in detail and the full paraxial form of the thermal blooming wave equation is derived from first principles. Refractive index changes in air caused by the passage of a 1 kW CW CO2 Gaussian laser beam are studied theoretically and both linear and non-linear cases examined. In the linear case, it is predicted that the laser beam produces a refractive index change of greater than 1 part in 10<super> 5</super> for a 1 second beam exposure. In the non-linear case, the iterative scheme developed predicts self-interaction and beam break-up after less than 0.5 s. For an annular beam, refractive index changes of 3 parts in 10 are predicted for the linear case. The influence of refractive index fluctuations on microwave radiation is modelled using a ray-tracing algorithm to investigate the behaviour of microwave radiation in an atmospheric waveguide. For a step-index guide of 5 cm radius, there is strong guiding so that even with a small perturbation in refractivity, rays with a wide range of launch angles are trapped. In the case of a guide with a quadratic refractive index profile, small changes in refractive index (1 part in 10<super>6</super>) produce weak guiding where only rays with trajectories very close to the optic axis are trapped. As the refractive index change increases, more divergent rays are trapped until a transition to strong guiding occurs at a critical value (changes in refractive index of the order of 1 part in 10<super>4</super>). A number of implementations of the waveguiding concept are proposed and evaluated. For the purposes of an experimental verification, a specially designed Annular Beam Director ("ABD") of an on-axis type is tested. Annular laser beams are propagated over short distances in the laboratory and the results presented. Measurements made with a rotating wire laser beam analyser indicate that the ABD performs well. Experiments designed to measure refractive index changes caused by a 1 kW CW CO2 laser beam of Gaussian profile are described. Measurements are made at wavelengths of 633 nm using a specially configured Michelson interferometer and at 3 mm using a millimetre wave quasi-optical FM noise measurement system. Typical results indicate refractive index changes of the order of 1 part in 106 at both the wavelengths considered. The guiding of microwave radiation is verified using a 1 kW CW CO2 annular laser beam, produced by the ABD, into which microwave energy is injected using a small copper reflector located at the centre of the annulus. In one implementation, the microwave energy is coupled out of the guide with a second copper reflector. In a second implementation, the microwave detector imit is located on the optic axis and the laser beam is terminated in an annular beam dump. The results show clear evidence that the high power laser beam forms a waveguide, increasing the amount of microwave radiation reaching the detector by a factor of 1.5.
en
University of St Andrews
The University of St Andrews
TK7871.65C7
Atmospheric guiding of electromagnetic waves
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/137572019-04-01T10:02:31Zcom_10023_126com_10023_31col_10023_129
Sibbett, Wilson
Kennedy, Gordon T.
150 p.
2018-06-06T10:00:31Z
2018-06-06T10:00:31Z
1994-07
http://hdl.handle.net/10023/13757
The work reported in this thesis is primarily concerned with the generation of ultrashort pulses from a NaCl:OH- colour-centre laser. Active mode locking of the NaCl:OH- laser by synchronous pumping and acousto-optic loss modulation was characterised in detail. Synchronously mode-locked pulses of 8 ps duration were compressed to 250 fs in an anomalously-dispersive optical fibre and a novel soliton-effect pulse compressor was constructed from a nonlinear fibre-loop mirror. Using this device, the synchronously mode-locked pulses were compressed to 300 fs with no discernible background radiation. The NaChOH- laser was coupled-cavity-mode locked using both nonlinear Fabry- Perot and Michelson cavity configurations, and pulses of 110 fs duration were obtained. A sawtooth amplitude modulation of the laser output was observed. This modulation, which arose from the beating of the mode-locked Nd:YAG pump laser and NaCl:OH- laser pulse trains, was avoided by frequency-referencing the colour-centre laser to the pump laser. A characterisation of the phase noise of the frequency-referenced, coupled-cavity mode- locked laser was performed. By replacing the frequency synthesiser for the pump laser mode locker with a crystal oscillator, the phase noise of both the Nd:YAG pump laser and the NaCl:OH- colour-centre laser were reduced by two orders of magnitude. The technique of self-mode locking was successfully applied to the NaCl:OH- laser. For this laser, it was necessary to include a rod of high-nonlinearity lead-silicate glass in the laser cavity to achieve sufficient self focusing for self-mode locking. Stable mode-locking was initiated by a regenerative acousto-optic modulation and pulses of 95 fs were obtained. The thesis concludes with descriptions of some experiments performed using a mode-locked NaCl:OH- laser and a KCl:TiO(1) colour-centre laser. Efficient pulsed Raman amplification in an optical fibre was achieved by using an optical fibre thats group-velocity dispersion was the same for both the pump and signal wavelengths. By co-propagating pulse trains from the KCl:TiO(1) and NaCl:OH- lasers through a semiconductor optical amplifier cross phase modulation was observed. Ultrafast all-optical switching using the nonlinearity at half the bandgap was demonstrated for an GaA1As integrated interferometer. This nonlinearity was subsequently used to coupled-cavity mode lock the KCl:TiO(1) colour-centre laser.
en
University of St Andrews
The University of St Andrews
TK7871.3K3
Lasers
Novel mode-locking techniques for colour-centre lasers
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/270842023-04-27T21:21:31Zcom_10023_126com_10023_31col_10023_129
Korolkova, Natalia
Nordgren, Viktor Manuel
Engineering and Physical Sciences Research Council (EPSRC)
171
2023-03-02T09:30:45Z
2023-03-02T09:30:45Z
2023-06-12
http://hdl.handle.net/10023/27084
https://doi.org/10.17630/sta/316
1947916
In the first half of this thesis, we present two models of ancilla-based quantum computation
(ABQC). Computation in the ABQC models is based on effecting changes on a register through
the interaction with and manipulation of an ancillary system. The two models presented enable
quantum computation through only unitary control of the ancilla – the ancilla-controlled model
(ACQC) – or supplemented by measurements on the ancilla which drive the register transfor-
mations – the ancilla-driven model (ADQC). For each of the models, we work on systems which
couple two continuous variables (CV) or which are hybrid: the register is formed by two-level
systems while the ancilla is a CV degree of freedom.
The initial models are presented using eigenstates of momentum as the ancillas. We move
to a more realistic scenario by modelling the ancillas as finitely squeezed states. We find that
the completely unitary ACQC contains persistent entanglement between register and ancilla in
the finite-squeezing scenario. In the ancilla-driven model, the effect of finite squeezing is to scale
the register state by a real exponential which is inversely proportional to the squeezing in the
ancilla.
In the second part, we cover work on Genuine Gaussian Multipartite Entanglement (Gaussian
GME). We present an algorithm for finding Gaussian states that have GME despite having
all two-state reductions separable. This touches on the idea of entanglement as an emergent
phenomenon. We determine GME via witnesses which probe only a subset of the state. We
therefore referred to them as partially blind witnesses. The algorithm is based on semi-definite
programs (SDPs). Such optimisation schemes can be used to efficiently find an optimal, partially
blind, GME witness for a given CM and vice versa. We then present results of multipartite states
of up to six parties. For the tripartite example, we present two experimental schemes to produce
the state using a circuit of beam-splitters and squeezers.
en
Creative Commons Attribution-ShareAlike 4.0 International
http://creativecommons.org/licenses/by-sa/4.0/
Quantum information
Quantum computation
Models of computation
Quantum correlations
Entanglement
Entanglement witness
Multipartite entanglement
Genuine multipartite entanglement
Semidefinite program
Emergent properties
Marginal problem
Hybrid ancilla-based quantum computation and emergent Gaussian multipartite entanglement
Thesis
Doctoral
PhD Doctor of Philosophy
The University of St Andrews
oai:research-repository.st-andrews.ac.uk:10023/233302024-03-11T11:33:09Zcom_10023_126com_10023_31col_10023_129
Gather, M. C. (Malte Christian)
Deng, Yali
China Scholarship Council (CSC)
University of St Andrews. School of Physics and Astronomy
xii, 184 p.
2021-06-07T16:57:05Z
2021-06-07T16:57:05Z
2021-06-28
https://hdl.handle.net/10023/23330
https://doi.org/10.17630/sta/71
en
University of St Andrews
The University of St Andrews
Data underpinning Yali Deng's thesis. Deng, Y., University of St Andrews. DOI: https://doi.org/10.17630/290effde-8e02-46a8-88d1-5ed9f6b25589
https://doi.org/10.17630/290effde-8e02-46a8-88d1-5ed9f6b25589
Title redacted
Thesis
Doctoral
PhD Doctor of Philosophy
2025-05-20
Thesis restricted in accordance with University regulations. Print and electronic copy restricted until 20 May 2025
oai:research-repository.st-andrews.ac.uk:10023/18602019-04-01T10:02:33Zcom_10023_126com_10023_31col_10023_129
Dholakia, Kishan
Gunn-Moore, Frank J.
Carnegie, David John
xvii, 198
2011-06-14T15:08:43Z
2011-06-14T15:08:43Z
2011
http://hdl.handle.net/10023/1860
In this thesis, experiments into artificially guiding neuronal growth cones using tightly focused laser beams were performed and evaluated.
The experiments are performed by focusing a laser beam to the leading edge of a developing growth cone and attempting to change the direction of growth cone. These experiments were carried out using Gaussian, line and asymmetric line beam profiles. There was no noticeable change in the success rate with different beam profiles.
Following this, I assisted my colleague Dr Michael Mazilu in the construction of a mathematical model of filopedia in an optical field in order to help explain the mechanism for optically guided neuronal growth which suggests that optical trapping forces on filopedia are responsible.
Next, I set about implementing a system to automate the process of laser guided neuron growth by employing a spatial light modulator and a custom-built computer program. This allowed the computer to track a developing growth cone and automatically adjust the position of the laser beam as the growth cone developed. This program was successfully employed to artificially grow neuronal growth cones towards a user-inputted target point. The use of the spatial light modulator to beam shape was also demonstrated with the use of a Bessel beam being used to guide neurons for the first time.
I also used a transgenic cell line of neurons to show for the first time that HSP70 is not involved in this phenomenon. This was accomplished by transfecting NG108’s with a plasmid containing HSP70 promoter tagged GFP. Under enough thermal or mechanical stress, the cells would express HSP70 which would produce a detectable GFP signal. No GFP was detected in cells after being exposed to laser irradiation of a power higher than would normally be used to guide neurons.
Combined, these experiments show that the beam profile of the operating laser does not significantly affect the success of artificial growth and that the optical force on filopedia near the laser beam is likely to be the mechanism for this phenomenon. A possible heating effect of the laser has also been shown to not be strong enough to elicit a heat shock stress response from the cell. The demonstration of an automatic system which incorporates beam shaping has also been shown and such a system shows the potential to advance the investigation of artificial neuron growth using lasers.
en
University of St Andrews
The University of St Andrews
QH515.C2
Photobiology
Neurons--Growth
Lasers in medicine
Optically guided neuronal growth
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/205312022-12-03T03:00:42Zcom_10023_126com_10023_31col_10023_129
King, Phil
Mackenzie, Andrew
Markovic, Igor
University of St Andrews
International Max Planck Research School for Chemistry and Physics of Quantum Materials (IMPRS-CPQM)
xviii, 142 p.
2020-09-01T11:05:20Z
2020-09-01T11:05:20Z
2020-07-27
http://hdl.handle.net/10023/20531
https://doi.org/10.17630/10023-20531
This thesis presents the study of electronic structure of two materials with strong spin-orbit coupling using angle-resolved photoemission spectroscopy (ARPES) experiments and density-functional theory (DFT) band calculations. The two materials are NbGeSb and Ca₃Ru₂O₇, which host weak and strong electronic interactions, respectively. While at first glance they seem rather disparate, I will show in both cases how novel phenomena emerge from the interplay of spin-orbit coupling and the crystal symmetries.
In NbGeSb, I combine insights from spin-integrated and spin-resolved ARPES measurements with DFT slab calculations to reveal how band inversion of two pairs of spin-orbit coupled surface states along the edge of the Brillouin zone results in a peculiar crossing structure with two protected and two asymmetrically gapped crossing points. I show how this is caused by the presence of a mirror symmetry line assigning definite mirror parity to orbital and spin angular momentum of the bands. This leads to a low-energy description of the crossing points equivalent to a two-dimensional Weyl equation, establishing them as 2D analogues of Weyl points.
In Ca₃Ru₂O₇, on the other hand, spin-orbit coupling provides a link between the electronic structure, the underlying antiferromagnetic order and the inherent antipolar distortion in the crystal structure. Our results reveal that a known structural and spin reorientation transition is caused by a spin-orbit derived gapping of a large Fermi surface. The hybridisation term couples the magnetic moment direction with the antipolar distortion of the crystal structure, and is only unlocked when the resulting electronic energy gain becomes enough to overcome the cost of spin reorientations.
These findings together highlight the abundance of possibilities for novel phenomena arising from the interplay of spin-orbit coupling and crystal symmetries in quantum materials.
en
University of St Andrews
The University of St Andrews
Max Planck Institute for Chemical Physics of Solids
Interplay of spin-orbit coupling and crystal symmetries in the electronic structures of NbGeSb and Ca₃Ru₂O₇ (thesis data) Marković, I., University of St Andrews. DOI: https://doi.org/10.17630/65018c0a-112c-41f8-b3da-1d1e7920445d
https://doi.org/10.17630/65018c0a-112c-41f8-b3da-1d1e7920445d
Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International
http://creativecommons.org/licenses/by-nc-nd/4.0/
Photoemission spectroscopy
Electronic structure
Crystal symmetries
Spin-orbit coupling
QC176.8E4M28
Electronic structure
Photoelectron spectroscopy
Energy-band theory of solids
Interplay of spin-orbit coupling and crystal symmetries in the electronic structures of NbGeSb and Ca₃Ru₂O₇
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/49072019-07-01T10:05:15Zcom_10023_126com_10023_31col_10023_129
Jardine, Moira
Llama, Joseph
163
2014-06-24T10:07:12Z
2014-06-24T10:07:12Z
2014-11-30
uk.bl.ethos.605818
http://hdl.handle.net/10023/4907
The search for planets orbiting stars other than the Sun has led to the discovery of over one thousand new worlds. The majority of these planets have been very large, Jupiter sized planets located very close to their host star. Transit surveys such as Kepler and SuperWASP monitor thousands of stars looking for periodic dips in light caused by a planet passing between our view point on Earth and their host star, blocking a fraction of the emitted star light.
One of the primary limitations in detecting a small, Earth sized planet comes from stellar activity induced signals within the data collected by exoplanet missions. These signals can, however, be used to our advantage. In this thesis, asymmetries in transit light curves are exploited to reveal properties of both the planet and the host stars themselves.
An asymmetry in the near-ultraviolet transit light curve of WASP-12b, one of the largest and hottest planets found to date is thought to be caused by the stellar wind interacting with the magnetic field surrounding the planet. In this thesis, a model for such an interaction is developed and is shown to be consistent with the observations, providing the first potential evidence for the presence of a magnetic field around an exoplanet. The model is then extended to predict the shape of near-ultraviolet light curves around HD 189733b, another hot Jupiter that orbits a very bright star. By looking at the variability in these transit light curves over time, the evolution and structure of the stellar wind is investigated.
By tracking the position of bumps in the transit light curve, it is shown here that the data collected by missions such as Kepler has the potential to reveal stellar butterfly patterns. Such patterns are intrinsically linked with the stellar dynamo which governs the properties of the stellar magnetic field.
Finally, the support of large-scale magnetic loops on young stars is investigated. These loops trap large amounts of hot, dense material and so a rapid destabilisation could lead to a flaring event, which could have devastating consequences for a nearby exoplanet.
en
University of St Andrews
The University of St Andrews
Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International
http://creativecommons.org/licenses/by-nc-nd/4.0/
Astronomy
Astrophysics
Exoplanets
Stars
Magnetic fields
QB820.L6
Extrasolar planets
Stars--Magnetic fields
Things that go bump in the light : an investigation into the effects of stellar activity on extrasolar planets
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/141562019-04-01T10:02:36Zcom_10023_126com_10023_31col_10023_129
Smith, Paul
Brown, Andrew J.W.
SERC
EEV ltd.
Royal and Signals Radar Establishment
180 p.
2018-06-18T09:20:44Z
2018-06-18T09:20:44Z
1988-07
http://hdl.handle.net/10023/14156
An X-ray preionised mercury bromide discharge laser (502-504 nm) has been designed, constructed and optimised. The double pulse forming line system built to drive the laser has proven to be both versatile and reliable. It utilises multiple-paralleled thyratrons and has demonstrated the characteristics required for long life operation of high average power gas discharge lasers. The supply produces a voltage pulse of 240 nsec duration and its output impedance is variable from 300 mO to 3.6O. With twelve thyratrons in parallel current risetimes of 83 kA musec-1 into a 300 mO matched load and 2 nsec jitter have been achieved. A voltage transient on the leading edge of the discharge pulse, to aid gas breakdown, up to 1½ times the line charge voltage is possible through a 'spike line' incorporated in the system. The X-ray preioniser, based on a cold cathode field emitter, produces an exposure of 5 mR in the discharge region which is adequate for effective preionisation of the laser. A full parametric study of the laser covering gas composition and pressure. X-ray source effects energy loading and other pulsed power supply effects has been carried out. The peak output energy recorded was 710 mJ with neon buffer gas at 4 atmospheres pressure. This represents an energy extraction of 0.5 JL-1. Pulse lengths of 92 nsec (FWHM) and efficiencies greater than 1.5 % have been achieved.
en
University of St Andrews
The University of St Andrews
TK7872.L3B8
Lasers
An X-ray preionised mercury bromide discharge laser
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/120142019-04-01T10:02:37Zcom_10023_126com_10023_31col_10023_129
Scholz, Alexander
Bozhinova, Inna
xxv, 147, [6] p.
2017-11-07T10:01:23Z
2017-11-07T10:01:23Z
2017-12-07
http://hdl.handle.net/10023/12014
Stars form inside clouds of molecular gas and dust. In the early stages of stellar evolution the remainders of the initial cloud form a circumstellar disk. For the next few million years the disk will slowly dissipate via accretion, outflows, photoevaporation and planet growth while the star makes its way onto the Main Sequence. This stage of a star’s life is referred to as the T Tauri phase and is characterised by high-level spectrophotometric variability. This thesis aims to study and map out the environments of T Tauri stars down to the very low mass regime by the means of time-domain monitoring.
Different physical processes in the system manifest themselves as variability on different time- scales as well as produce characteristic spectroscopic and photometric features at various wave- lengths. In order to study young stellar objects in depth, the observing campaigns presented in this work were designed to cover a large range of time-scales - minutes, hours, days and months. Combining all the data, this thesis establishes a baseline of over a decade for some objects. The observations also cover a wide range of wavelengths from the optical to the mid-infrared part of the spectrum.
The star RW Aur experienced two long-lasting dimming events in 2010 and 2014. This thesis presents a large collection of spectral and photometric measurements carried out just before and during the 2014 event. Spectral accretion signatures indicate no change in the accretion activity of the system. Photometry indicates that parallel to the dimming in the optical the star becomes brighter in the mid-infrared. The observations in this work combined with literature data suggest that the origin of the 2014 event is most likely obscuration of the star by hot dust from the disk being lifted into the disk wind.
Very low mass stars (<0.4 M⊙) are the most common type of star in the Galaxy. In order to understand the early stages of stellar evolution we must study young very low mass stars. This work investigates the photometric and spectroscopic variability of seven brown dwarfs in star forming regions near σ Ori and ε Ori. All targets exhibit optical photometric variability between from 0.1 to over 1.0 magnitude that persists on a time-scale of at least one decade. Despite the photometric variability no change in the spectral type is measured. In the cases where the stars are accreting, modelling of the spectral changes suggest the accretion flow is more homogeneous and less funnelled compared to Sun-like T Tauri stars. The non-accreting variables are more plausibly explained by obscuration by circumstellar material, possibly a ring made out of multiple clouds of dust grains and pebbles with varying optical depths.
The star-disk systems studied in this thesis have some broader implications for star and planet formation theory. The case-study of RW Aur has unambiguously demonstrated that the planet- forming environment is very dynamic and can change dramatically on short time-scales, which in turn would have implications for the diversity of planetary systems found in the Galaxy. The Orion stars have shown that the current theory for the T Tauri stage of stellar evolution is valid down to the very low mass regime. The seven dwarfs are a good example for the evolutionary path of circumstellar disks, showing the transition from gas-high, flared accretion disks (σ Ori) to dust-dominated, depleted, structured debris disks (ε Ori).
en
University of St Andrews
The University of St Andrews
Attribution-NonCommercial-NoDerivatives 4.0 International
http://creativecommons.org/licenses/by-nc-nd/4.0/
Variable stars
Young stellar objects
T Tau stars
Brown dwarfs
Star formation
Circumstellar disks
QB843.T12B7
T Tauri stars
Variable stars
Brown dwarf stars
Stars--Formation
Circumstellar matter
Protoplanetary disks
TOYS - time-domain observations of young stars
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/109722019-04-01T10:02:38Zcom_10023_126com_10023_31col_10023_129
Maitland, Arthur
Curry, Randy D.
219 p.
2017-06-09T12:05:14Z
2017-06-09T12:05:14Z
1992
uk.bl.ethos.661138
http://hdl.handle.net/10023/10972
The parameter space over which electron beams operate for pumping CO₂ lasers significantly extended. A repetitive pulsed power/electron beam system for the generation of 45 µs, 220 keV, electron beams for CO₂ lasers has been designed and implemented which can operate over a 6:1 impedance range. The system consists of a 150 kV – 250 kV modulator and a large area, (2.500 cm²) 5-20 mλ /cm² hot-cathode electron-beam gun. The system is designed and fabricated to be used in conjunction with an electron beam sustained laser and is capable of operating continuously at up to 10 pps.
The following thesis examines, in detail, the experimental and theoretical investigation of the modulator/electron beam subsystems which comprise the electron beam system. Parameters of the CO₂ laser which determine the electron beam parameter space, and thus the modulator characteristics, are reviewed. Both cold-cathode and hot-cathode pulsed current parameters are reviewed, and the cathode characteristics upon which the
hot-cathode was selected are discussed. The 132 thoriated tungsten filament, grid-controlled, hot-cathode gun used to generate the required 5-20 mλ/cm², 250 cm length source of electron beam with a spatial flatness of ± 10% is shown.
Based on the hot-cathode electron beam gun design, the theoretical and practical design characteristics of the hollow-cathode, thyratron switched, 1800 J, 10 pps, 250 kV modulator are shown. Design equations which allow selection of the modulator operation range, and selection of the modulator matching resistors used to match the fixed impedance modulator to the 6:1 electron beam impedance range with a pulse droop of less then 0.7% and a pulse flatness of ± 10% are derived. Moreover, a detailed discussion of the circuit simulations used to both tune and optimize the modulator's impedance tapered, Transformer-coupled Type E PFN to the four electron beam operating ranges are shown. Practical layout and design and the grounding and shielding principles employed in the system. Component spacings required to insure reliable modulator operation at 250kV are also considered.
The design and implementation of the 45 µs, SCR switched, transformer-coupled PFN based grid-pulser are discussed. The grid pulser characteristics including the 105-650 V, 28-166 A, pulse required to control the 5-20 mλ / cm²,hot-cathode current density are examined. Theoretical design equations are derived to allow, the Miller capacitance, and thus the time varying impedance of the grid-cathode region to be predicted. Circuit simulations showing the grid-pulser circuit interaction with the constant perveance, Miller capacitance dominated, grid-cathode load are discussed. Final layout of the SCR-switched, grid-pulser including design of the spiral inductors used for the PFN is reported. Specific layout details are shown which allow the grid pulser to operate reliably while floating at the 220 kV electron beam acceleration pulse.
A discussion of the subsystem experimental integration phase conducted at Pulse Sciences, Inc. is also presented in the following thesis. Test results of the modulator and grid-pulser into their respective electron beam loads are compared with the circuit simulations. Relevant vacuum flashover physics issues found during the experimental integration of the modulator, grid-pulser, and electron-beam gun are considered. Specific discussions of the vacuum, gap and vacuum insulator physics which effect the operation of the large area electron beam gun are reported. Included in this discussion is the experimental cold- cathode conditioning procedure used to condition the electron-beam gun to 250 kV. In-situ, hot-cathode filament carburization and activation procedures developed during the integration phase of the program are also presented, with a short discussion of the background mass spectra measured during the experiments. Finally, the experimental characterization. of the spatial uniformity of the electron beam is reported along with a short summary of the investigation results.
en
University of St Andrews
The University of St Andrews
TK7872.L3C8
Lasers
Design and operation of a 45 μs repetitively pulsed 12 mw electron beam for a CO₂ laser
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/260322022-09-17T02:01:01Zcom_10023_126com_10023_31col_10023_129
Samuel, Ifor D.W.
Lian, Cheng
Engineering and Physical Sciences Research Council (EPSRC)
xiv, 161 p.
2022-09-16T13:36:04Z
2022-09-16T13:36:04Z
2022-11-29
http://hdl.handle.net/10023/26032
https://doi.org/10.17630/sta/200
EP/L015110/1
en
Creative Commons Attribution 4.0 International
http://creativecommons.org/licenses/by/4.0/
2023-08-26
Thesis restricted in accordance with University regulations. Restricted until 26th August 2023
TK7871.89L53L5
Title redacted
Thesis
Doctoral
PhD Doctor of Philosophy
The University of St Andrews
oai:research-repository.st-andrews.ac.uk:10023/136002019-04-01T10:02:39Zcom_10023_126com_10023_31col_10023_129
Smith, Paul
Wilson, Colin Richard
211 p. 11 p. of plates.
2018-05-30T08:32:35Z
2018-05-30T08:32:35Z
1992-07
http://hdl.handle.net/10023/13600
This thesis is concerned with the development of Transmission Line Transfomer (TLT) pulsed power supplies and the generation of fast risetime (>50ns), good quality, high repetition-rate voltage pulses for flash x-ray preionisors and other applications. It explains the principle of the TLT and reports on two TLT pulsed power supplies that have been built. The first, or prototype, produced output voltage pulses with risetimes of 50ns and durations of 200ns and was used to power a flash x-ray preionisation source for a mercury bromide laser. The second, a 50kV, 100? device, was built as part of a wider research program concerned with the development of space based pulsed power supplies. The development of ceramic tile technology is also described and the relevant electrical, mechanical and thermal properties of some barium titanate tiles given; it is then shown how ceramic tiles can be used to construct compact pulse generators for TLT systems. Finally, the subject of nonlinear dielectric pulse sharpening is introduced and pulse sharpening in a delay line ladder network containing air-core inductors and non-linear capacitors is demonstrated. It is then explained how these lines can be used to improve the output risetime of a TLT.
en
University of St Andrews
The University of St Andrews
TK7868.P8W5
Pulse circuits
The design and development of fast pulsed power supplies using transmission line transformers
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/145992019-04-01T10:02:40Zcom_10023_126com_10023_31col_10023_129
Derrick, G. H.
Wynne, Valerie Anne
Science Research Council (Great Britain)
170 p.
2018-06-26T11:04:49Z
2018-06-26T11:04:49Z
1971
http://hdl.handle.net/10023/14599
The hypothesis adopted in this work is that any permissible metric field whatsoever must satisfy the field equations deduced from an action principle in which the Lagrangian is quadratic in the components of the Riemann curvature tensor. The adoption of such a hypothesis is motivated by the precariousness of the general relativistic interpretation of Mach's principle, which is often used to justify a phenomenological approach to the theory. The quadratic action principle is chosen to provide the fundamental equations of the gravitational field because it is logically and aesthetically appealing, and causes us to lose nothing of the standard relativity theory based on Einstein's vacuum equations. The set of relationships, Rp𝜎 - ½9p𝜎R = -k Tp𝜎 (Equation) retained as a definition of the matter tensor Tp𝜎. Attention is concentrated on the solutions of the (generally fourth order) fundamental field equations in the static, spherically symmetric case. Sets of exact, series and numerical solutions are obtained corresponding to certain boundary conditions, or with certain properties in common. Study of the geometrical, topological and physical properties of several of the universes obtained as a result of our hypothesis leads us to believe that our theory is not implausible. We conclude by considering the further possibilities of the theory.
en
University of St Andrews
The University of St Andrews
QC178.W8
Gravitation
A theory of gravitation incorporating the quadratic action principle of relativity
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/145582019-04-01T10:02:41Zcom_10023_126com_10023_31col_10023_129
ter Haar, D.
Green, C. D.
108 p.
2018-06-25T15:05:50Z
2018-06-25T15:05:50Z
1954
http://hdl.handle.net/10023/14558
This thesis is concerned with the consideration of the H-theorem in a statistical manner and the information that may be derived from it as to the variation with time of an isolated mechanical system, and especially the approach to equilibrium. A historical introduction is given in which it shown how the need for such a statistical approach arose, and hoy the question of the behaviour of the fluctuations about the values of H predicted by the unrestricted H-theorem became important. The type of behaviour suggested by the Ehrenfests is quoted and to verify this it is found to be necessary to consider in detail actual models. Two classical models, the urn model and the wind-wood model, are considered, and then the procedure is generalized so as to include the whole class of models of the type consisting of two groups of particles, the one group moving and interacting with the members of the second group which are fixed. The transition probabilities and the rate of change of H, and the mean time of recurrence of a fluctuation are found for these models by considering the influence of fluctuations upon the Stosszahlansatz values for the numbers of collisions. The results confirm the postulates of the Ehrenfests. In assumptions common to the statistical treatment of collision processes.
en
University of St Andrews
The University of St Andrews
QC175.G8
Statistical mechanics
The statistical aspects of Boltzmann's H-Theorem
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/90752019-04-01T10:02:42Zcom_10023_126com_10023_31col_10023_129
Mackenzie, Andrew
Zhao, Lishan
Scottish Universities Physics Alliance (SUPA)
Engineering and Physical Sciences Research Council (EPSRC)
Scottish Doctoral Training Centre in Condensed Matter Physics (CM-CDT)
University of St Andrews
Max-Planck-Gesellschaft zur Förderung der Wissenschaften
China Scholarship Council (CSC)
200 p.
2016-07-04T15:54:19Z
2016-07-04T15:54:19Z
2016-06-22
uk.bl.ethos.690335
http://hdl.handle.net/10023/9075
At low temperatures, strongly correlated materials, which typically contain partially filled d- or f-electron shells, often exhibit phases with interesting properties,
which may be of both research value and technological significance. The mechanisms of phase formation in them if could be clarified, are believed to be able
to provide important insights not only into physics but also into the design of
new materials. In this thesis, the experimental study of two strongly correlated
materials, Sr₂RuO₄ and CeAuSb₂ is presented.
Sr₂RuO₄ is an unconventional superconductor, and a strong candidate for spin-triplet superconductivity. Its potential significance in relation to quantum computing also makes it of great scientific interest. In order to clarify the role of the
Van Hove singularity (VHS) in its superconductivity, experimental study has been
performed with the recently developed uniaxial strain methods. The experimental
results suggest that as the sample is compressed towards the VHS, the transition
temperature can be enhanced by a factor of =2.3 whilst the upper critical field
can be enhanced by a factor of more than ten. The experimental findings are
intriguing and new possibilities are open for future study.
CeAuSb₂ is a Kondo lattice system which has been speculated to be close to
a quantum critical point. The similarity between some of its low temperature
properties and those of a well-known quantum critical system Sr₃Ru₂O₇ makes
it especially interesting. In this thesis, new magnetoresistivity and torque magnetometry measurements are used to clarify its low temperature phase diagram, and
reveal the strength of its magnetic anisotropy.
en
University of St Andrews
The University of St Andrews
QC173.458E43Z5
Condensed matter--Electric properties
Condensed matter--Magnetic properties
Phase transformations (Statistical physics)
Superconductivity
Uniaxial strain and high magnetic field investigation on materials with novel order parameters
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/19012019-04-01T10:02:42Zcom_10023_126com_10023_31col_10023_129
Feix, Martin
Scottish Universities Physics Alliance (SUPA)
174
2011-06-23T12:12:16Z
2011-06-23T12:12:16Z
2011-06-24
http://hdl.handle.net/10023/1901
Despite the many successes of the current standard model of cosmology on the largest physical scales, it relies on two phenomenologically motivated constituents, cold dark matter and dark energy, which account for approximately 95% of the energy-matter content of the universe. From a more fundamental point of view, however, the introduction of a dark energy (DE) component is theoretically challenging and extremely fine-tuned, despite the many proposals for its dynamics. On the other hand, the concept of cold dark matter (CDM) also suffers from several issues such as the lack of direct experimental detection, the question of its cosmological abundance and problems related to the formation of structure on small scales. A perhaps more natural solution might be that the gravitational interaction genuinely differs from that of general relativity, which expresses itself as either one or even both of the above dark components. Here we consider different possibilities on how to constrain hypothetical modifications to the gravitational sector, focusing on the subset of tensor-vector-scalar (TeVeS) theory as an alternative to CDM on galactic scales and a particular class of chameleon models which aim at explaining the coincidences of DE. Developing an analytic model for nonspherical lenses, we begin our analysis with testing TeVeS against observations of multiple-image systems. We then approach the role of low-density objects such as cosmic filaments in this framework and discuss potentially observable signatures. Along these lines, we also consider the possibility of massive neutrinos in TeVeS theory and outline a general approach for constraining this hypothesis with the help of cluster lenses. This approach is then demonstrated using the cluster lens A2390 with its remarkable straight arc. Presenting a general framework to explore the nonlinear clustering of density perturbations in coupled scalar field models, we then consider a particular chameleon model and highlight the possibility of measurable effects on intermediate scales, i.e. those relevant for galaxy clusters. Finally, we discuss the prospects of applying similar methods in the context of TeVeS and present an ansatz which allows to cast the linear perturbation equations into a more convenient form.
en
University of St Andrews
The University of St Andrews
Scottish Universities Physics Alliance (SUPA)
Alternative relativistic models
Cosmology: Theory
Dark energy
Dark matter
General relativity
Gravitational lensing
Physics beyond the standard model
Structure formation
QC178.F45
Gravitation
Cosmology
General relativity (Physics)
Dark energy (Astronomy)
Dark matter (Astronomy)
Gravitational lenses
Extragalactic and cosmological tests of gravity theories with additional scalar or vector fields
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/77982019-07-01T10:05:33Zcom_10023_126com_10023_31col_10023_129
Cameron, A. C.
Haywood, Raphaëlle D.
Science and Technology Facilities Council (STFC)
171
2015-11-17T10:42:55Z
2015-11-17T10:42:55Z
2015-11-30
uk.bl.ethos.675202
http://hdl.handle.net/10023/7798
The detection of low-mass extra-solar planets through radial-velocity searches is currently limited by the intrinsic magnetic activity of the host stars. The correlated noise that arises from their natural radial-velocity variability can easily mimic or conceal the orbital signals of super-Earth and Earth-mass extra-solar planets. I developed an intuitive and robust data analysis framework in which the activity-induced variations are modelled with a Gaussian process that has the frequency structure of the photometric variations of the star, thus allowing me to determine precise and reliable planetary masses.
I applied this technique to three recently discovered planetary systems: CoRoT-7,
Kepler-78 and Kepler-10. I determined the masses of the transiting super-Earth
CoRoT-7b and the small Neptune CoRoT-7c to be 4.73 ± 0.95 M⊕ and 13.56 ±
1.08 M⊕, respectively. The density of CoRoT-7b is 6.61 ± 1.72 g.cm⁻³, which is
compatible with a rocky composition. I carried out Bayesian model selection to
assess the nature of a previously identified signal at 9 days, and found that it is best
interpreted as stellar activity. Despite the high levels of activity of its host star, I
determined the mass of the Earth-sized planet Kepler-78b to be 1.76 ± 0.18 M⊕.
With a density of 6.2(+1.8:-1.4) g.cm⁻³, it is also a rocky planet. I found the masses of Kepler-10b and Kepler-10c to be 3.31 ± 0.32 M⊕ and 16.25 ± 3.66 M⊕, respectively. Their densities, of 6.4(+1.1:-0.7) g.cm⁻³ and 8.1 ± 1.8 g.cm⁻³, imply that they are both of rocky composition – even the 2 Earth-radius planet Kepler-10c!
In parallel, I deepened our understanding of the physical origin of stellar radial-velocity variability through the study of the Sun, which is the only star whose surface can be imaged at high resolution. I found that the full-disc magnetic flux is an excellent proxy for activity-induced radial-velocity variations; this result may become key to breaking the activity barrier in coming years.
I also found that in the case of CoRoT-7, the suppression of convective blueshift leads to radial-velocity variations with an rms of 1.82 m.s⁻¹, while the modulation induced by the presence of dark spots on the rotating stellar disc has an rms of 0.46 m.s⁻¹. For the Sun, I found these contributions to be 2.22 m.s⁻¹ and 0.14 m.s⁻¹, respectively. These results suggest that for slowly rotating stars, the suppression of convective blueshift is the dominant contributor to the activity-modulated radial-velocity signal, rather than the rotational Doppler shift of the flux blocked by starspots.
en
University of St Andrews
The University of St Andrews
“Planets and Stellar Activity: Hide and Seek in the CoRoT-7 system”, R. D. Haywood, A. Collier Cameron, D. Queloz, S.C.C. Barros, M. Deleuil, R. Fares, M. Gillon, A.F. Lanza, C. Lovis, C. Moutou, F. Pepe, D. Pollacco, A. Santerne, D. Segransan and Y. C. Unruh, 2014, Monthly Notices of the Royal Astronomy: 443, 2517
“The Sun as a planet-host star: Proxies from SDO images for HARPS radial-velocity variations”, R. D. Haywood, A. Collier Cameron, Y. C. Unruh, C. Lovis, A. F. Lanza, J. F. Llama, M. Deleuil, R. Fares, M. Gillon, C. Moutou, F. Pepe, D. Pollacco, D. Queloz, and D. Segransan, submitted for publication to Monthly Notices of the Royal Astronomy
Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International
http://creativecommons.org/licenses/by-nc-nd/4.0/
Exoplanet detection
Stellar activity of Sun-like stars
Sunspots, faculae/plage
Super-Earths
Exoplanet characterisation
Radial-velocity technique
QB820.H2
Extrasolar planets--Detection
Stars--Magnetic fields
Stars--Motion in line of sight
Hide and seek : radial-velocity searches for planets around active stars
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/25532019-07-01T10:04:18Zcom_10023_126com_10023_31col_10023_129
Driver, Simon Peter
Vika, Marina
160
2012-04-12T14:56:58Z
2012-04-12T14:56:58Z
2012-06
http://hdl.handle.net/10023/2553
Over recent years there has been an increase of the number of secure supermassive black hole (SMBH) detections. These SMBH measurements have lead astronomers to establish well defined empirical relationships between the SMBH mass and some of the properties of the host galaxy. The number of galaxies with SMBH mass measurements is currently limited to about 100. One approach of expanding the study of the SMBH is to use the empirical relations for estimating M[subscript(bh)] for larger samples of galaxies. The investigation of the SMBH population (or SMBH mass function) for large sample of galaxies in the nearby universe has helped to
constrain the SMBH and the galaxy evolution.
Previous estimates of the SMBH mass function at low redshift were produced mainly by combining the measurements of the galaxy luminosity or velocity function with one of the SMBH scaling relations. In the first part of the thesis I will present an independent construction of the nearby supermassive black hole mass function by applying the optical M[subscript(bh)]–L relation onto the Millennium Galaxy Catalogue (MGC).
Additionally, in the second part I will provide photometric analysis of all UKIDSS galaxies for which SMBH masses have been measured. I will derive composite profiles of brightness, ellipticity and position angles of each galaxy. I will show that the Sérsic function fits the brightness profile of the majority of the elliptical galaxies and the bulge of disk galaxies and I will provide alternative multi-component fits when necessary. Then these photometric parameters will be used for constructing the M[subscript(bh)]–L relation in the near-IR and to investigate the M[subscript(bh)]–n relation.
In the third part I will construct the near-IR SMBH mass function for the Galaxy and Mass Assembly (GAMA) survey. For this purpose I will apply the newly derived M[subscript(bh)]–L relation onto an elliptical subsample of K-band images. The advantage of this SMBH mass function is that during the M[subscript(bh)]–L construction I used the same quality images and techniques used on the GAMA survey. Apart from the M[subscript(bh)]–L relation, the M[subscript(bh)]–sigma relation was used as an alternative approach for a subsample of galaxies for which the velocity dispersions were available. Furthermore, I employed both local SMBH mass functions (MGC & GAMA) for estimating the SMBH mass density at redshift zero and accounted for the dependence of the total SMBH density on the look-back time by comparing with semi-analytic SMBH mass functions. Finally, from the SMBH mass density I estimated the baryon fraction that is locked into SMBHs.
en
University of St Andrews
The University of St Andrews
Creative Commons Attribution 3.0 Unported
http://creativecommons.org/licenses/by/3.0/
Galaxies
Photometry
Supermassive black hole
Bulge
QB843.B55V5
Black holes (Astronomy)--Mathematical models
Galaxies--Evolution
Galaxies--Formation
Astronomical photometry
Supermassive black holes : the local supermassive black hole mass function
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/71102019-04-01T10:02:45Zcom_10023_126com_10023_31col_10023_129
Edwin, R. P.
Clampin, Mark
Science and Engineering Research Council (SERC)
335 p.
2015-08-04T08:49:28Z
2015-08-04T08:49:28Z
1986
uk.bl.ethos.571484
http://hdl.handle.net/10023/7110
A large format two dimensional photon counting detector has
been evaluated as a detector for astronomical spectroscopy. The
design comprises an 320 photocathode, a tandem MCP gain stage and a
circular arc terminated resisitive anode to provide pOSitional
coordinates of detected events. The system is run from an LSI 11/23
computer operating under FORTH control.
The micro-channel plate operating characteristics and the
detector's resolution, quantum efficiency and imaging performance
have been studied. The principal areas requiring design improvement
are found to be the micro-channel plate gain,
processing and photocathode quality.
electronic signal
The detector has been employed in a observing program on a
0.5 m telescope. Spectra of IAU faint radial velocity standards and
the eclipsing binary system s-l Cam have been obtained and analysed
to assess the system's performance.
en
University of St Andrews
The University of St Andrews
QB465.A6C6
Investigation of a resistive anode detector for astronomical spectroscopy
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/46502019-07-01T10:16:12Zcom_10023_126com_10023_31col_10023_129
Hill, Philip W.
Parker, Quentin Andrew
Science and Engineering Research Council (SERC)
478 p.
2014-04-29T09:47:53Z
2014-04-29T09:47:53Z
1986
uk.bl.ethos.571485
http://hdl.handle.net/10023/4650
A thorough and detailed investigation into the accuracy,
reliability and consistency of the objective-prism redshift technique
with changes in plate material, measuring machine and reduction
techniques has been undertaken. Providing that the limitations of the
procedures involved are appreciated, useful 3-D information, accurate
to Z ~±0.01, for large numbers of faint galaxies may be obtained from
single UKST fields. A surface brightness correction has enabled the
technique to be extended to galaxies as bright as bj ~15.8. The
validity of the results were confirmed by external calibration with
slit-spectra. The slit-spectra results obtained have more than
doubled the size of the calibration sample available and have further
vindicated the applicability of the technique.
Analysis of the 107 slit-spectra redshifts determined revealed
the existence of considerable structure in the field studied, with
significant density enhancements and voids being apparent. This
structure has been confirmed on larger scales and to greater depths
with the subsequent analysis of ~1,500 objective-prism redshifts from
COSMOS data of the field. Two large superclusters were discovered.
The first centred at Z ~0.05 but extending for at least 150 h⁻¹Mpc,
and the second a projected filament of connecting clusters at Z ~0.11
and 23 h⁻¹Mpc long. A selection of 2-D and 3-D statistical analysis
techniques have been used to describe the observed large-scale galaxy
distribution in this field.
A by-product of this work has been the discovery of a new and
powerful means of star/galaxy separation based on magnitude
comparisons between paired objects from both the direct and
objective-prism plates. This technique has revealed ~20% stellar
contamination in the star/galaxy separation based on direct plate data alone. In conclusion, objective-prism galaxy redshifts are valuable
information for complementing 2-D data in the study of the large-scale
distribution of galaxies from COSMOS measures of Large numbers of UKST
plates. To this end an automatic technique of objective-prism
redshift determination should be developed.
en
University of St Andrews
The University of St Andrews
Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International
http://creativecommons.org/licenses/by-nc-nd/4.0/
QB901.P2
Objective-prism and slit-spectra redshifts in a study of the distribution of galaxies
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/139692019-05-11T02:02:52Zcom_10023_126com_10023_31col_10023_129
Smith, Graham Murray
Motion, Claire Louise
Engineering and Physical Sciences Research Council (EPSRC)
xxxi, [3], 185, [8] p.
2018-06-12T14:50:08Z
2018-06-12T14:50:08Z
2018-06-27
http://hdl.handle.net/10023/13969
Pulsed dipolar spectroscopy (PDS) is an electron paramagnetic resonance (EPR) technique,
used to conduct long range distance measurements in proteins in the nanometre range. This
thesis presents a number of methodological and instrumental techniques to improve the sensitivity and utility of PDS experiments using a home-built high power pulsed spectrometer,
HiPER, operating at 94 GHz. These include the implementation of phase-modulated composite pulses, which correct for imperfections arising due to inhomogeneity, and offer increased
excitation bandwidth as well as experimental protocols such as annealing and glassing of samples. A theoretical study into the use of matched filtering to reduce echo noise during measurements, has predicted gains of up to a factor of 3 enhancement in signal-to-noise.
Using such techniques we demonstrate sensitivity enhancements of more than 30 on PDS
experiments, between nitroxides and Fe centres, in haem-proteins, corresponding to a reduction in averaging time of almost 1,000, in comparison to standard commercial spectrometers
operating at X-band. The use of composite pulses in PDS experiments on nitroxide biradicals
were also investigated, including their limitations due to intramolecular effects. The thesis
then describes a single frequency dipolar modulation experiment, RIDME, and uses high field
measurements to determine both the distance and relative orientation of a cobalt-nitroxide
system, for the first time. Finally, a design study is conducted to implement frequency and
amplitude modulated pulses on a spectrometer at 9/34 GHz to improve sensitivity.
en
University of St Andrews
The University of St Andrews
Electron paramagnetic resonance
Pulsed dipolar spectroscopy
Instrumentation
Magnetic resonance
Electron paramagnetic resonance spectroscopy
Improving the sensitivity and utility of pulsed
dipolar experiments in EPR at 94 GHz
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/129322019-04-01T10:02:47Zcom_10023_126com_10023_31col_10023_129
Dholakia, Kishan
Rhodes, Daniel Paul
xx, 285 p.
2018-03-13T16:43:02Z
2018-03-13T16:43:02Z
2005
http://hdl.handle.net/10023/12932
This thesis is concerned with the guiding of cold atoms using optical forces, which is of great importance in the field of atom optics. Atomic beams can be used for precision sensor equipment, building nano-scale structures, construction of quantum computers and to further the understanding of the properties of atoms. Atoms are guided along light beams using the dipole force; there are two regimes under which this force works. Typically red-detuned guides are used (atoms are attracted towards the light) such guides, however, require large detuning and high powers. In this thesis we investigate the use of blue-detuned (atoms are repelled from the light) hollow light beams of moderate power (a few hundred mW) and confine atoms in the dark centre of the beams. Several magneto-optical traps (MOTs) have been constructed to exploit different guiding geometries. Hollow beams have been generated using a variety of methods; in particular the use of a computer controlled spatial light modulator (SLM) has provided great versatility and simplicity to the experimental arrangements. First, experiments were performed with a low-velocity intense source (LVIS) of atoms. A co-linear LG beam significantly enhances the observed flux, however, considerable difficulties are encountered loading atoms into oblique guides. Imaging a hole in the walls of the light tube was used to improve the loading efficiency. Second, guiding a free-falling atom cloud is performed using a non-diffracting Bessel beam. It is found that while the potential of the Bessel beam is steeper than equivalent LG beams the power distribution across the beam severely limits its usefulness. The next study investigated higher-order LG guide beams generated with an SLM. High order modes have a narrower profile so confine the atoms with less interaction with the guide beam, leading to a more natural guide (as opposed to a pushing force). Finally the SLM was used to create non-trivial beam shapes for beam splitters and interferometers.
en
University of St Andrews
The University of St Andrews
QC173.4A85R5
Atomic beams.
Laser cooling.
Magnetooptical devices.
Light modulators.
Beam splitters.
Optical interferometers.
Experimental studies of cold atom guiding using hollow light beams
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/145932019-04-01T10:02:48Zcom_10023_126com_10023_31col_10023_129
Friedman, Lionel Robert
Robertson, Neil
179 p.
2018-06-26T10:26:25Z
2018-06-26T10:26:25Z
1977
http://hdl.handle.net/10023/14593
This thesis describes theoretical research into multiphonon non-radiative transitions in solids. These processes occur when an impurity centre electron which has been raised to an excited state returns to its ground state by emitting phonons into the lattice rather than by emitting light. The original contribution of this thesis is concerned with certain theoretical aspects of non-radiative transitions. For the first time the Molecular Crystal Model originally developed by Holstein to study small-polaron motion is used to investigate this problem. In particular, the effect that weak dispersion of the vibrational modes has on the transition rates is studied. The inclusion of weak dispersion is essential for a rigorous treatment of non-radiative transitions, and without this feature the transition rates are not well defined. We also use the well-known single configuration coordinate model to derive recombination rates, giving particular attention to the unequal frequency case. Finally an adaptation of the Molecular Crystal Model is considered which more closely resembles real physical systems in that the electron is coupled to both crystalline modes and a local mode.
en
University of St Andrews
The University of St Andrews
QC176.8E9R7
Exction theory
Non-radiative transitions
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/189382021-04-08T15:46:08Zcom_10023_126com_10023_31col_10023_129
Di Falco, Andrea
Li, Xin
China Scholarship Council (CSC)
University of St Andrews. School of Physics and Astronomy
xii, 166 p.
2019-11-15T13:50:26Z
2019-11-15T13:50:26Z
2019-12-03
http://hdl.handle.net/10023/18938
https://doi.org/10.17630/10023-18938
My PhD is focused on the design, fabrication and optoelectronic applications of epsilon-near-zero
(ENZ) metamaterials (MMs), which have vanishing real part of the permittivity and
support fascinating optical effects, including light squeezing, sub-wavelength imaging, enhanced
directive emission and enhanced non-resonant optical nonlinearity. Different approaches have
been developed to realise ENZ media, such as tuning the modal dispersion in narrow plasmonic
channels, exploiting the natural dispersion of transparent conductive oxides and creating composite
structures with metals and dielectrics. As a platform with exotic physical properties, ENZ media
also exhibit enormous potentials in combination with tunability and various nanofeatures in the
photonic and plasmonic regimes.
This thesis demonstrates two approaches to achieve the ENZ condition. One method is to stack
metal (Ag) and dielectric (SiO2) layers periodically at sub-wavelength scales. The resulting material
behaves as an effective medium with an average permittivity close to zero, and we show that
this ENZ medium can enhance the emission of quantum dots. This approach generally requires
nanofabrication techniques developed for flat and rigid substrates, for example, the electron beam
evaporation, which are not always applicable to micro- and macroscopic devices with arbitrary
shapes. To surpass these limitations, we design and experimentally demonstrate an optical freestanding and low-loss ENZ membrane in the visible range, by layering polymer (SU-8) and Ag
nano-layers. Additionally, we propose a method to introduce both flexibility and electrical tunability
into ENZ media by replacing the metal layer with a 2D material, graphene, in the multilayer model.
The other way to obtain an ENZ response is using natural materials which operate in proximity
of their plasma frequency, typically here the indium tin oxide (ITO) at the near-infrared
range. The ITO thin films are deposited using radio frequency magnetron sputtering, and their
permittivities are manipulated via controlling fabrication parameters. We succeed in sweeping the
zero-permittivity frequency of ITO media by controlling the gas recipe and deposition temperature
during the sputtering process. To obtain specific optical responses, the ENZ ITO thin films are
designed to be combined with different photonic features, including nanoantenna on microsphere
and nanohelix, associated with a direct fabrication approach based on electron beam induced
deposition (EBID).
Furthermore, this thesis extends the research range by realising the photonic trimming of
quantum emitters via various metallic nanofeatures fabricated directly using EBID method. We
believe that the interaction of ENZ MMs with EBID approach offers an opportunity to create hybrid
ENZ platforms for optoelectronic applications.
en
University of St Andrews
The University of St Andrews
Epsilon-near-zero metamaterials for optoelectronic applications (thesis data). Li, X., University of St Andrews, 2019. DOI: https://doi.org/10.17630/c87e32ae-936d-43ba-ac9d-6877197e8342
https://doi.org/10.17630/c87e32ae-936d-43ba-ac9d-6877197e8342
TK7871.15M48L5
Metamaterials
Optoelectronics
Epsilon-near-zero metamaterials for optoelectronic applications
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/177932021-02-16T17:00:58Zcom_10023_126com_10023_31col_10023_129
Bonnell, Ian Alexander
Ramon Fox, Felipe Gerardo
European Research Council (ERC)
University of St Andrews. St Leonard's College
xxiii, 223 p.
2019-05-31T16:07:37Z
2019-05-31T16:07:37Z
2019-06-24
http://hdl.handle.net/10023/17793
https://doi.org/10.17630/10023-17793
Star formation begins on the large scales of a galaxy and takes place on the smallest scales. As the interstellar gas flows into a spiral arm, it forms a shock where the change in density, coupled to self-gravity and thermal instabilities, leads to the formation of high density structures where molecular clouds grow. It is important to understand the role of large-scale flows in assembling these clouds. This work explores the gas flows in spiral arms to understand its role on molecular cloud formation comparing between grand-design and flocculent galaxies.
A set of high-resolution smoothed particle hydrodynamics (SPH) simulations are used. One simulation evolves the gas in a potential including a halo, stellar disc, and spiral arms. The second simulation evolves the gas in an N-body stellar disc and bulge within a fixed halo potential. The first and second models are representative of grand-design and flocculent galaxies, respectively. The third simulation is a high-resolution simulation of a region of gas flowing in a spiral arm based on the simulations of Bonnell et al. (2013), which follows in more detail the local cloud dynamics. In the global models, the mass resolution is about 45M⊙ per gas particle and in the spiral simulation, about 0.6M⊙.
The results show that in both the grand-design and flocculent models, the gas is shocked as it flows through an arm. The N-body model shows flow characteristics qualitatively similar to the spiral potential model but with more variations due to the potentials arm-to-arm variations. Clouds are identified using a friends-of-friends algorithm to catalogue clumps above a given density threshold. These have non-negligible streaming motions and their properties are consistent with observed mass-radius and size-velocity dispersion relations.
"This work was supported by the ERC ECOGAL project under grant
number 291277. I also thank the University of St. Andrews for supporting me with a St.
Leonards Scholarship." -- Acknowledgements
en
University of St Andrews
The University of St Andrews
The role of large scale flows in molecular cloud formation in spiral galaxies (Thesis data) Ramon Fox, F.G., University of St Andrews, 22 May 2019 DOI: https://doi.org/10.17630/0b6aa0a8-d46a-4660-ad87-320c982746ee
https://doi.org/10.17630/0b6aa0a8-d46a-4660-ad87-320c982746ee
Attribution-NonCommercial-NoDerivatives 4.0 International
http://creativecommons.org/licenses/by-nc-nd/4.0/
Hydrodynamics
Interstellar medium -- Kinematics and dynamics
Interstellar medium -- Molecular clouds -- Formation
Galaxies -- Kinematics and dynamics
Milky Way -- Structure
Astrophysics -- Astrophysics of galaxies
QB791.4R2
Molecular clouds
Galactic dynamics
Spiral galaxies
The role of large scale flows in molecular cloud formation in spiral galaxies
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/147882019-04-01T10:02:49Zcom_10023_126com_10023_31col_10023_129
Sibbett, Wilson
Yelland, Carl
Engineering and Physical Sciences Research Council (EPSRC)
211 p.
2018-07-02T11:01:13Z
2018-07-02T11:01:13Z
1997-06
http://hdl.handle.net/10023/14788
In this thesis the design, construction and performance of several diode-laser pumped continuous-wave neodymium lasers are described. These lasers were operated both around 1 mum and, by internal frequency-doubling, at 0.5 mum. The main emphasis has been on the assessment of the various laser designs with regard to their potential for efficient, high-power visible operation. A variety of pumping geometries, resonator configurations, gain media and internal frequency-doubling schemes were investigated, and their relative merits explored. Both side-pumping and end-pumping arrangements were employed, with Nd:YAG, Nd:YLF and Nd:YVO4 being used as gain media. Travelling-wave and standing-wave resonator designs were used. The polarisation-rotation effect in non- planar ring resonators was investigated and used to obtain single-frequency output. Single-frequency 0.5 mum powers up to 1.2 W were generated, and the highest 0.5 mum output power achieved was 4 W on two-longitudinal modes spaced by 450 MHz. The highest 1 mum output power achieved was 10 W, with a slope efficiency of 43%. Maximum pump powers for the lasers were in the region 15 - 35 W. A review of diode-laser pumped devices is included, with particular emphasis on the role of the spatial distributions of the pump and signal fields, because this is an important limiting factor in the performance of diode-pumped bulk laser systems. The criteria governing the harmonic output power when internally frequency-doubling are discussed. Issues relating to noise in the harmonic output, and techniques for its avoidance, are also discussed.
en
University of St Andrews
The University of St Andrews
TK7872.L3Y3
Lasers
Diode-pumped IμM neodymium lasers and their internal frequency doubling
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/284382023-10-20T08:18:05Zcom_10023_126com_10023_31col_10023_129
Cyganowski, Claudia Jane
Bonnell, Ian Alexander
Zhang, Suinan
University of St Andrews
China Scholarship Council (CSC)
160
2023-09-25T08:32:34Z
2023-09-25T08:32:34Z
2023-11-29
http://hdl.handle.net/10023/28438
https://doi.org/10.17630/sta/618
180023582
201806190010
The earliest phase of high-mass star formation has remained a challenging topic. The distinguishing feature between competing theoretical models is the prediction for the high-mass prestellar cores. This thesis presents (sub)arcsecond-resolution interferometric observations in conjunction with synthetic observations at submillimeter wavelengths towards high-mass pre-/proto-stellar objects, for the purpose of characterising the physical and kinematic properties of the early stages of high-mass star formation.
Chapter two showcases deep ALMA 0.82 mm observations (θ ∼ 0.5′′) towards the high-mass prestellar core candidate G11.92-0.61 MM2. Extensive N2H+ (4-3) emission is detected around MM2, displaying complex spectra with multiple velocity components present. Gaussian decomposition and hierarchical clustering are performed to the N₂H⁺ data cube to investigate the kinematics of the N₂H⁺-emitting gas, which reveals a hierarchical system with filamentary substructures showing velocity gradients. The most dominant N₂H⁺ substructure probably traces the accretion flows towards MM2. A mass inflow rate of 2 ×10⁻⁴ ∼ 1.2 ×10⁻³ M⊙ yr⁻¹ is derived with the hypothesis of filamentary accretion flows.
Chapter three presents synthetic 1.3 mm dust continuum images of high-mass star-forming clumps generated with analytic prescriptions and radiative transfer modelling. 432 models with different combinations of stellar masses, separations of sources, and beam sizes are considered. This parametric study predicts that the low-mass objects with masses ≦ 1 M⊙ will not be detected if located ≦ 0.1 pc from a 50 M⊙ protostar in 0.5′′observations.
Chapter four summarises the SMA 1.3 mm observations towards the high-mass protostellar object G34.24+0.13MM. The 1′′ 1.3 mm continuum image reveals that G34.24+0.13MM is a single compact core, with a size of 4700 AU and a mass of 12.5 M⊙. Molecular lines are detected towards the source, possibly indicating ordered motions of the gaseous envelope or unresolved multiplicity. The uniquely high luminosity-mass ratio of G34.24+0.13MM requires future higher-resolution multi-wavelength observations to properly explain.
en
Synthetic images of massive protoclusters (thesis data)
Zhang, S., University of St Andrews, 22 Sept 2023. DOI: https://doi.org/10.17630/74981de8-9380-41cd-a384-81f73f7b13b3, https://almascience.nrao.edu/aq/?result_view=observations, https://lweb.cfa.harvard.edu/cgi-bin/sma/smaarch.pl
https://doi.org/10.17630/74981de8-9380-41cd-a384-81f73f7b13b3
https://almascience.nrao.edu/aq/?result_view=observations
https://lweb.cfa.harvard.edu/cgi-bin/sma/smaarch.pl
Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International
http://creativecommons.org/licenses/by-nc-nd/4.0/
High-mass star formation
Cluster formation
Interferometry
Synthetic observation
QB806.Z5
Stars--Formation
Interferometry
The formation of high-mass stars and stellar clusters
Thesis
Doctoral
PhD Doctor of Philosophy
The University of St Andrews
oai:research-repository.st-andrews.ac.uk:10023/149502019-04-01T10:02:50Zcom_10023_126com_10023_31col_10023_129
Dunn, Malcolm H.
Padgett, Miles
Gibson, Graham Martin
185 p.
2018-07-05T08:16:39Z
2018-07-05T08:16:39Z
1999-05
http://hdl.handle.net/10023/14950
This thesis describes the development and applications of single-frequency, continuously tunable, continuous-wave (cw), optical parametric oscillators (OPOs). Two doubly-resonant OPOs (DROs) are presented, one providing tunable light around 1?m, the other specifically designed as a spectroscopic source for methane near 1649nm. Once stabilised, the frequency-selective nature of the DRO ensures operation on a single mode-pair without the need for additional intracavity frequency-selective components. Both DROs are smoothly tunable by smoothly tuning the pump laser. The 1mum DRO is based on a bulk KTP crystal cut for near-degenerate, type-II, critical phase-matching (theta= 90°, ϕ = 37°). Angle tuning the crystal provides coarse tuning of the output frequencies over a range of ~50nm. Small perturbations to the OPO cavity is sufficient to cause a systematic mode-hop and provides a method of tuning across the phase-matching bandwidth (~0.5THz). This DRO is demonstrated as a spectroscopic source by recording the absorption spectrum of cesium molecules near 1050nm. The DRO as a potentially compact source of tunable light is demonstrated by using a frequency-doubled microchip laser as the pump source. The output consists of a single pair of signal and idler modes even when using a multilongitudinal-mode pump laser. Smooth tuning of the output frequencies is achieved by temperature tuning the pump laser. The 1.65mum DRO is based on periodically poled KTiOPO4 (PPKTP). The suitability of PPKTP for cw OPOs was first assessed by a difference frequency generation experiment from which the effective d33 coefficient was estimated to be ~5mum/V. The idler wavelength is coarsely tuned at a rate of 0.73nm/°C by varying the crystal temperature. A combination of computer modelling and experimental observation is used to study the dynamic behaviour of a DRO. The numerical model calculates the time required for the OPO to build-up from the parametric fluorescence and is in excellent agreement with experimental observations.
en
University of St Andrews
The University of St Andrews
TK7872.O7G5
Ocillators
Optical parametric oscillators
Continuously frequency-tunable CW optical parametric oscillators and their application to spectroscopy
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/129442019-04-01T10:02:51Zcom_10023_126com_10023_31col_10023_129
Horne, Keith
Bramich, Daniel Martyn
ix, 162 p.
2018-03-14T16:15:38Z
2018-03-14T16:15:38Z
2005
http://hdl.handle.net/10023/12944
We present results from 30 nights of observations of the intermediate-age Solar-metallicity open cluster NGC 7789 with the WFC camera on the INT telescope in La Palma. From ~900 epochs, we obtained lightcurves and Sloan r' - i' colours for ~33000 stars, with ~2400 stars with better than 1% precision. We find 24 transit candidates, 14 of which we can assign a period. We rule out the transiting planet model for 21 of these candidates using various robust arguments. For 2 candidates we are unable to decide on their nature, although it seems most likely that they are eclipsing binaries as well. We have one candidate exhibiting a single eclipse for which we derive a radius of 1.81+/0.09- Three candidates remain that require follow-up observations in order to determine their nature. Monte Carlo simulations reveal that we expected to detect ~2 transiting 3d to 5d hot Jupiter planets from all the stars in our sample if 1% of stars host such a companion and that a typical hot Jupiter radius is similar to that of HD 209458b. Our failure to find good transiting hot Jupiter candidates allows us to place an upper limit on the 3d to 5d hot Jupiter fraction of 2.6% for all stars at the 1% significance level, and similar useful limits on the hot Jupiter fraction of the different star types in our sample.
en
University of St Andrews
The University of St Andrews
QB820.B82
Extrasolar planets--Remote sensing.
Transits.
Transiting extra-solar planets in the field of open cluster NGC 7789
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/98942019-04-01T10:02:52Zcom_10023_126com_10023_31col_10023_129
Leonhardt, Ulf
Korolkova, Natalia
Sahebdivan(i), Sahar
Scottish Overseas Research Student Awards Scheme (SORSAS)
Engineering and Physical Sciences Research Council (EPSRC)
xvi, 137 p.
2016-11-29T08:14:24Z
2016-11-29T08:14:24Z
2016-11-30
http://hdl.handle.net/10023/9894
The resolution of optical instruments is normally limited by the wave nature of light. Circumventing this limit, known as the diffraction limit of imaging, is of tremendous practical importance for modern science and technology. One method, super-resolved fluorescence microscopy was distinguished with the Nobel Prize in Chemistry in 2014, but there is plenty of room for alternatives and complementary methods such as the pioneering work of Prof. J. Pendry on the perfect lens based on negative refraction that started the entire research area of metamaterials. In this thesis, we have used analytical techniques to solve several important challenges that have risen in the discussion of the microwave experimental demonstration of absolute optical instruments and the controversy surrounding perfect imaging. Attempts to overcome or circumvent Abbe’s diffraction limit of optical imaging, have traditionally been greeted with controversy. In this thesis, we have investigated the role of interacting sources and detectors in perfect imaging. We have established limitations and prospects that arise from interactions and resonances inside the lens. The crucial role of detection becomes clear in Feynman’s argument against the diffraction limit: “as Maxwell’s electromagnetism is invariant upon time reversal, the electromagnetic wave emitted from a point source may be reversed and focused into a point with point-like precision, not limited by diffraction.” However, for this, the entire emission process must be reversed, including the source: A point drain must sit at the focal position, in place of the point source, otherwise, without getting absorbed at the detector, the focused wave will rebound and the superposition of the focusing and the rebounding wave will produce a diffraction-limited spot. The time-reversed source, the drain, is the detector which taking the image of the source. In 2011-2012, experiments with microwaves have confirmed the role of detection in perfect focusing. The emitted radiation was actively time-reversed and focused back at the point of emission, where, the time-reversed of the source sits. Absorption in the drain localizes the radiation with a precision much better than the diffraction limit. Absolute optical instruments may perform the time reversal of the field with perfectly passive materials and send the reversed wave to a different spatial position than the source. Perfect imaging with absolute optical instruments is defected by a restriction: so far it has only worked for a single–source single–drain configuration and near the resonance frequencies of the device. In chapters 6 and 7 of the thesis, we have investigated the imaging properties of mutually interacting detectors. We found that an array of detectors can image a point source with arbitrary precision. However, for this, the radiation has to be at resonance. Our analysis has become possible thanks to a theoretical model for mutually interacting sources and drains we developed after considerable work and several failed attempts. Modelling such sources and drains analytically had been a major unsolved problem, full numerical simulations have been difficult due to the large difference in the scales involved (the field localization near the sources and drains versus the wave propagation in the device). In our opinion, nobody was able to reproduce reliably the experiments, because of the numerical complexity involved. Our analytic theory draws from a simple, 1–dimensional model we developed in collaboration with Tomas Tyc (Masaryk University) and Alex Kogan (Weizmann Institute). This model was the first to explain the data of experiment, characteristic dips of the transmission of displaced drains, which establishes the grounds for the realistic super-resolution of absolute optical instruments. As the next step in Chapter 7 we developed a Lagrangian theory that agrees with the simple and successful model in 1–dimension. Inspired by the Lagrangian of the electromagnetic field interacting with a current, we have constructed a Lagrangian that has the advantage of being extendable to higher dimensions in our case two where imaging takes place. Our Lagrangian theory represents a device-independent, idealized model independent of numerical simulations. To conclude, Feynman objected to Abbe’s diffraction limit, arguing that as Maxwell’s electromagnetism is time-reversal invariant, the radiation from a point source may very well become focused in a point drain. Absolute optical instruments such as the Maxwell Fisheye can perform the time reversal and may image with a perfect resolution. However, the sources and drains in previous experiments were interacting with each other as if Feynman’s drain would act back to the source in the past. Different ways of detection might circumvent this feature. The mutual interaction of sources and drains does ruin some of the promising features of perfect imaging. Arrays of sources are not necessarily resolved with arrays of detectors, but it also opens interesting new prospects in scanning near-fields from far–field distances. To summarise the novel idea of the thesis:
• We have discovered and understood the problems with the initial experimental demonstration of the Maxwell Fisheye.
• We have solved a long-standing challenge of modelling the theory for mutually interacting sources and drains.
• We understand the imaging properties of the Maxwell Fisheye in the wave regime.
Let us add one final thought. It has taken the scientific community a long time of investigation and discussion to understand the different ingredients of the diffraction limit. Abbe’s limit was initially attributed to the optical device only. But, rather all three processes of imaging, namely illumination, transfer and detection, make an equal contribution to the total diffraction limit. Therefore, we think that for violating the diffraction limit one needs to consider all three factors together. Of course, one might circumvent the limit and achieve a better resolution by focusing on one factor, but that does not necessary imply the violation of a fundamental limit. One example is STED microscopy that focuses on the illumination, another near–field scanning microscopy that circumvents the diffraction limit by focusing on detection. Other methods and strategies in sub-wavelength imaging –negative refraction, time reversal imaging and on the case and absolute optical instruments –are concentrating on the faithful transfer of the optical information. In our opinion, the most significant, and naturally the most controversial, part of our findings in the course of this study was elucidating the role of detection. Maxwell’s Fisheye transmits the optical information faithfully, but this is not enough. To have a faithful image, it is also necessary to extract the information at the destination. In our last two papers, we report our new findings of the contribution of detection. We find out in the absolute optical instruments, such as the Maxwell Fisheye, embedded sources and detectors are not independent. They are mutually interacting, and this interaction influences the imaging property of the system.
EPSRC grant for the QUEST project (The Quest for Ultimate Electromagnetic using Spatial Transformations )
en
University of St Andrews
The University of St Andrews
University of Vienna
Attribution-ShareAlike 4.0 International
http://creativecommons.org/licenses/by-sa/4.0/
Super-resolution
Maxwell fisheye lens
Transformation optics
Electromagnetic fields on curved manifolds
Space-time analogy by transformation optics
Overcoming the diffraction limit
QC385.S25
Optical instruments
Lenses
The enigma of imaging in the Maxwell fisheye medium
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/71302019-04-01T10:02:53Zcom_10023_126com_10023_31col_10023_129
Lesurf, J. C. G.
Harvey, Andrew R.
Science and Engineering Research Council (SERC)
National Physical Laboratory
viii, 264 p.
2015-08-05T10:33:49Z
2015-08-05T10:33:49Z
1991
uk.bl.ethos.637513
http://hdl.handle.net/10023/7130
This thesis describes the work undertaken in the design and
construction of a millimetre wave, quasi-optical impedance bridge. The
instrument operates as a nulling complex reflectometer, with nulling
being implemented at the signal frequency by interferometric optical
techniques. In principle, the quasi-optical components of the
reflectometer are operable in the frequency range 80 GHz to 500 GHz,
though the range of continuous coverage is determined by the waveguide
components and antennas used to couple sources and detectors into the
Gaussian beams.
Gaussian beam mode theory has been employed in the design and
measurement of the quasi-optical components, which behaved as
expected. Phase and polarisation effects within the impedance bridge
were modelled and the consequent behaviour of the impedance bridge
predicted. A comparison of these predictions with early results led to
refinement of the model. This model is based upon a more complete
description of the transmissivities and reflectivities of the wire grid
polarising beam splitters and accurately predicts the instrument
behaviour.
A data acquisition and control system has been built to facilitate
automated operation of the impedance bridge. This system is interfaced
to an Acorn® Archimedes microcomputer and the hardware and
software has been developed to enable interrupt driven data acquisition.
The reflectivity of a quasi-optical load has been measured at 85 GHz
with an accuracy and standard deviation of better than 0.1 % In
amplitude and a standard deviation of better than 0.10° in phase.
The quasi-optical half cube and computer interface components
developed in this work form the basis of a stock of general purpose
modules now in everyday use at St. Andrews.
en
University of St Andrews
The University of St Andrews
TK7868.B7H2
A millimetre wave, quasi-optical complex impedance bridge
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/46042019-07-01T10:05:23Zcom_10023_126com_10023_31col_10023_129
Hill, Philip W.
Malaney, Robert A.
x, 275 p.
2014-04-24T15:39:41Z
2014-04-24T15:39:41Z
1986
uk.bl.ethos.571489
http://hdl.handle.net/10023/4604
The origin of the extreme hydrogen deficiency observed in the R
Coronae Borealis (RCrB) stars remains poorly understood. A likely
mechanism for producing this deficiency is one whereby the original
hydrogen envelope of the star is engulfed and destroyed in its
interior. One of the few RCrB stars so far analysed, U Aquarii, in fact
shows emphatic evidence of such an event having indeed occurred. This
evidence takes the form of the large s-process enhancements observed in
U Aquarii. Such enhancements are caused by the production of
significant neutron fluxes which are directly produced by envelope
engulfment
giving rise to the ¹²C(p, γ) ¹³N(β⁺γ) ¹³C(α,n) ¹⁶O sequence of
nuclear reactions. In order to obtain vital information regarding the
nature of the envelope mixing event from observed s-process
enhancements, detailed nucleosynthesis calculations investigating
neutron production and s-process synthesis are carried out using a
series of nuclear reaction networks and covering a wide range of
parameter space. These calculations are mainly based on low-mass AGB
and post-AGB stellar models since it is widely believed that the RCrB's
are in some way related to this group of stars. It is shown how the
ingestion rate of envelope material, the initial abundances and the type
of mixing model used have a large influence on the neutron and s-process
production.
New spectral observations of U Aquarii are presented, and it is
shown how these new observations allow a new interpretation of the
mixing event which occurred in this star and how further improved
abundance data of the star will lead to an unambiguous determination of
the nature of the mixing event. The RCrB stars are also thought to be
related to the extreme helium stars. Discovery of variability in two of
these latter stars is presented.
en
University of St Andrews
The University of St Andrews
Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International
http://creativecommons.org/licenses/by-nc-nd/4.0/
QB806.M2
A study of U Aquarii and the nucleosynthesis of neutrons and S-process elements in evolved stars of low mass
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/61372022-08-10T11:49:04Zcom_10023_126com_10023_31col_10023_129
Penedo, Carlos
Samuel, Ifor D. W.
Quinn, Steven D.
Engineering and Physical Sciences Research Council (EPSRC)
xxvi, 368 p.
2015-02-23T21:46:33Z
2015-02-23T21:46:33Z
2014-06-25
http://hdl.handle.net/10023/6137
Alzheimer’s disease (AD) is characterised by a series of biomolecular aggregation events, which include the formation of neurotoxic protein structures composed of the β-amyloid (Aβ) peptide. In this thesis, fluorescence self-quenching (FSQ) between fluorescently-labelled peptides is introduced as a strategy for detecting and characterizing Aβ aggregates in solution, and for overcoming limitations associated with conventional methods. Using a combination of steady-state, picosecond time-resolved fluorescence and transmission electron microscopy, the fluorescence response of HiLyte Fluor 555-labelled Aβ peptides is characterised to demonstrate that Aβ self-assembly organizes the covalently attached probes in close proximity to trigger the self-quenching sensing process over a broad range of conditions. Importantly, N-terminal tagging of β-amyloid peptides is shown to not alter the self-assembly kinetics or the resulting aggregated structures. When performed in Förster resonance energy transfer (FRET) format, this method becomes a ratiometric platform to gain insights into amyloid structure and for standardizing in vitro studies of amyloid self-assembly. The ability of FSQ-based methods to monitor the inhibition of Aβ aggregation by model test compounds including the small heat shock protein (Hsp), the amyloid-binding alcohol dehydrogenase protein (ABAD) and bovine serum albumin (BSA) is also demonstrated.
Given that Aβ is formed within the cell membrane and is known to induce its disruption, sophisticated single-molecule fluorescence spectroscopy methods were developed to quantify membrane dynamics induced by the presence of disrupting agents, such as Aβ and detergents. The solubilisation dynamics of single liposomes induced by the non-ionic surfactant Triton-X 100 (TX-100) were studied in real-time. Using this approach, the swelling and permeabilization steps of the solubilisation process were unambiguously separated within single FRET trajectories, and their kinetic details as a function of Triton-X 100 and presence of cholesterol within the membrane structure were examined. Finally, single-molecule stepwise-photobleaching techniques were employed to study the effect of Aβ oligomers interacting with supported-lipid bilayers, establishing a platform from which to investigate how the presence of a membrane layer affects Aβ oligomerization at the level of individual molecules.
Overall, the fluorescence-based strategies for amyloid- and liposome-sensing presented in this work bridges the gap between current morphology-specific techniques and highly-specialized single-molecule methods to provide a biophysical toolbox to investigate the changes in structure, size and molecular interactions accompanying the amyloid aggregation pathway and for the screening of novel therapeutic and diagnostic agents.
en
University of St Andrews
The University of St Andrews
Amyloid aggregation
Alzheimer's disease
β-amyloid peptide
Amyloid polymorphism
Fluorescence quenching
Forster resonance energy transfer (FRET)
QP519.9F56Q5
Fluorescence spectroscopy
Cell aggregation
Alzheimer's disease--Molecular aspects
Amyloid beta protein
Advanced optical techniques to study biomolecular aggregation processes
Thesis
Doctoral
PhD Doctor of Philosophy
2023-03-18
Thesis restricted in accordance with University regulations. Electronic copy restricted until 18th March 2023
oai:research-repository.st-andrews.ac.uk:10023/203542022-08-03T02:01:35Zcom_10023_126com_10023_31col_10023_129
Jardine, Moira
Lehmann, Lisa Theres
Scottish Universities Physics Alliance (SUPA)
University of St Andrews
xxix, 185 p.
2020-07-28T15:57:59Z
2020-07-28T15:57:59Z
2020-07-27
http://hdl.handle.net/10023/20354
https://doi.org/10.17630/10023-20354
Good knowledge about cool star magnetic activity, topology and cycles is crucial to find a
second solar system and to better understand ours. The Zeeman-Doppler-Imaging (ZDI) surveys,
which unveil the stellar magnetic field topology, have now run for long enough to detect
solar-like activity cycles. This is a good point to review what ZDI detects robustly and how to
interpret the resulting ZDI maps. As ZDI only detects the large-scale magnetic field an important
question to answer is: What can we learn from the large-scale field topology about the
small-scale field for solar-like stars?
I connect 3D non-potential flux transport simulations based on the Sun with the observational
ZDI technique. First, I decomposed the magnetic field topology of the simulations
into different length-scales. I discovered that the large-scale field reflects global properties of
the small-scale field emergence for slowly-rotating solar-like stars. Second, I used synthetic
line profiles modelled from the simulations as input for ZDI. I showed that ZDI can recover
the hints of the small-scale flux emergence in the observable large-scale field for slow rotators
but recovers approximately one order of magnitude lower magnetic energy. The maximum
entropy regularisation used in ZDI prevents the correct reconstruction of the magnetic energy
distribution but ZDI can recover the fractions of the different field components reasonably
well.
To examine if ZDI can recover solar-like cycles, I applied ZDI to non-potential flux transport
simulations modelling the solar magnetic field over 15 years. I discovered that the axisymmetric
poloidal fraction and the axi- and non-axisymmetric energy are the best parameters to
track solar-like activity cycles while the averaged large-scale field or the total energy show no
or misleading trends.
"I acknowledge support from the Scottish Universities Physics Alliance (SUPA) prize studentship
and the University of St Andrews Higgs studentship. Further, I received supplementary
founding for travelling from SUPA and the European Southern Observatory (ESO) for a
8-weeks short term visit at the ESO Headquarters in 2017 and the ESO for supporting a second
visit (1-month) in 2018. Further, I received a travel grant to visit the Cool Stars 20 Conference
in Boston to present the work displayed in Chapter 4 from the Royal Astronomical Society
(RAS)." -- Funding
en
University of St Andrews
The University of St Andrews
Connecting simulations and observations for solar-like stars (thesis data) Lehmann, L.T., University of St Andrews, 2019. DOI: https://doi.org/10.17630/ae078167-03ea-4af6-9055-c3147e13c286
https://doi.org/10.17630/ae078167-03ea-4af6-9055-c3147e13c286
Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International
http://creativecommons.org/licenses/by-nc-nd/4.0/
Magnetic fields
Stars
Sun
Zeeman-Doppler-imaging
Spectropolarimetry
QB843.C6L4
Cool stars
Stars--Magnetic fields--Computer simulations
Stars--Magnetic fields--Observations
Sun
Cool star magnetic field topologies : connecting simulations and observations for solar-like stars
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/145332019-04-01T10:02:55Zcom_10023_126com_10023_31col_10023_129
Wan, Kong K.
Powis, J. J.
220 p.
2018-06-25T11:40:55Z
2018-06-25T11:40:55Z
1994
http://hdl.handle.net/10023/14533
We give a brief review of geometric quantisation up to and including the Blattner-Kostant-Sternberg kernal. In general this leads to symmetric operators that are not essentially self-adjoint so motivating a study of Hermitian operators as observables in a generalised quantum mechanics. We show that a generalised squaring axiom can reproduce the results of Blattner-Kostant-Sternberg quantisation. We also show that quantisation with respect to polarisations with compact leaves gives results that conflict with the nonlocal nature of quantum mechanics. We develop a front form quantum mechanics of a free scalar particle using geometric quantisation. The front and instant forms are related via unitary maps derived from the pairing which intertwines quantisations with respect to the forms. The front form position operator has a maximally symmetric component so we are compelled to work within the framework of a generalised quantum mechanics; the result in there being no Hegerfeldt type instantaneous spreading of initially localised wavefunctions in the front form. Finally we show that this model can be lifted to a many particle free field theory.
en
University of St Andrews
The University of St Andrews
QC174.1Q2P7
Quantum theory
Geometric quantisation and quantum mechanics in Dirac's front form
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/147902019-04-01T10:02:57Zcom_10023_126com_10023_31col_10023_129
Sibbett, Wilson
Valentine, Gareth J.
294 p.
2018-07-02T11:01:22Z
2018-07-02T11:01:22Z
1999-03
http://hdl.handle.net/10023/14790
This thesis concerns the generation of tunable ultrashort pulses near the 1.55 mum telecommunications window. Two principal laser systems are considered: i) the NaCl:OH colour-centre laser, which employs the technique of synchronously-pumped modelocking to generate tunable picosecond pulses and ii) the self-modelocked Cr4:YAG laser to generate femtosecond pulses tunable from 1.5-1.56 mum. Details are given for an all-solid-state cw and cw-modelocked pump source for Cr4:YAG and colour-centre lasers based on Nd:YAG. Fibre-coupled AlGaAs laser diodes are employed as the solid-state pump source to this laser. When operated cw, up to 8.5 W of linearly polarised output power in a TEM00 beam is obtained. A compact cw actively-modelocked Nd:YAG laser is described having a pulse repetition rate of 194 MHz. Pulse durations down to 34 ps and output powers up to 6.0 W are obtained from this system. An 82 MHz Nd:YVO4 laser is also detailed producing pulsewidths down to 75 ps and average output powers up to 3.5 W. The intrinsic noise source associated with the synchronous modelocking technique is discussed and a simple passive stabilisation scheme, coherent-photon-seeding (CPS), is described and applied to the synchronously-modelocked NaCl:OH laser. Results of a simulation of this laser are reported and a comparison is made with the practical observations of the stabilised laser. For the first time, theoretical and experimental evidence for the presence of high frequency pulse jitter in synchronously-pumped- modelocked (SPML) lasers is presented and the coherent photon seeding technique is shown to eliminate this noise. Details are also given for the construction of a compact, all-solid-state, femtosecond Cr4+:YAG laser. A design prescription for laser resonators having a high propensity for self-modelocking is presented and an unconventional 3-mirror resonator is adopted for optimised self-modelocked operation. Using this design, modelocked output powers up to 300 mW with 120 fs pulses from a compact, regeneratively initiated laser having a pulse repetition rate of 320 MHz is reported for 4.7W incident pump power. Self- modelocking is demonstrated for pump powers down to ~1W with this cavity design. A compact cavity design for self-modelocking is also assessed, with a footprint of just 20 X 25 cm, which places a prism in each cavity arm. 470 fs pulses at 220 mW average output power are reported.
en
University of St Andrews
The University of St Andrews
TK7872.L3V2
Lasers
Development of all-solid-state modelocked laser sources at 1.55 μM
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/7422019-04-01T10:02:58Zcom_10023_126com_10023_31col_10023_129
Lee, Stephen
Heron, David Owen Goudie
155
2009-08-27T14:03:06Z
2009-08-27T14:03:06Z
2009
http://hdl.handle.net/10023/742
The archetypal high temperature superconductor Bi₂Sr₂CaCu₂O[subscript[8+δ]] has been extensively investigated. However, until now, little has been known about the behaviour of the
magnetic vortices inside the Vortex Glass and liquid state. µSR measurements have shown
a negative skewness for the field probability distributions in these regimes. Such a negative
skewness has only recently been explained as being a direct consequence of three-body correlations between vortices in a similar layered superconductor. With a new understanding
and knowledge of the physics of these systems, it is instructive to re-visit the superconductor Bi₂Sr₂CaCu₂O[subscript[8+δ]] to explain the evolution of these three-body correlations occurring here.
Comparing this with the ion-irradiated superconductors (of the same Bi₂Sr₂CaCu₂O[subscript[8+δ]] material), allows one to observe how three-body correlations between vortices evolve differently to that in the pristine material. Moreover, in the region of the macroscopic irreversibility
line, entropically driven disorder exists below the matching field B[subscript[ϕ]] , whilst there is the appearance of relatively straight vortex lines at fields above B[subscript[ϕ]] . Such phenomena suggest a
significant di fference in the evolution of three-body correlations compared with the unirradiated material.
There has been much work conducted on the interplay between superconductivity
and magnetism in materials of reduced dimensions. Work presented here on the ferromagnet/superconductor trilayer system (Permalloy/Nb/Permalloy) has shown a novel magnetic
profile at the interface between the ferromagnetic and superconducting boundary, where,
contrary to what is expected, the magnetism appears to be significantly suppressed at the
interface before increasing towards the centre of the Nb layer.
45070623 bytes
application/pdf
en
University of St Andrews
The University of St Andrews
QC611.98M34H4
Superconductors
Vortex-motion
Crystals--Magnetic properties
Thin films--Magnetic properties
A study of superconductivity in single crystals and thin films using muon-spin rotation and neutron scattering
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/120792019-04-01T10:03:01Zcom_10023_126com_10023_31col_10023_129
Helling, Christiane
Hodosán, Gabriella
191
2017-11-14T09:39:33Z
2017-11-14T09:39:33Z
2017-12-07
http://hdl.handle.net/10023/12079
Lightning is an important electrical phenomenon, known to exist in several Solar System planets. Amongst others, it carries information on convection and cloud formation, and may be important for pre-biotic chemistry. Exoplanets and brown dwarfs have been shown to host environments appropriate for the initiation of lightning discharges. In this PhD project, I aim to determine if lightning on exoplanets and brown dwarfs can be more energetic than it is known from Solar System planets, what are the most promising signatures to look for, and if these "exo-lightning" signatures can be detected from Earth.
This thesis focuses on three major topics. First I discuss a lightning climatology study of Earth, Jupiter, Saturn, and Venus. I apply the obtained lightning statistics to extrasolar planets in order to give a first estimate on lightning occurrence on exoplanets and brown dwarfs. Next, I introduce a short study of potential lightning activity on the exoplanet HAT-P-11b, based on previous radio observations. Related to this, I discuss a first estimate of observability of lightning from close brown dwarfs, with the optical Danish Telescope. The final part of my project focuses on a lightning radio model, which is applied to study the energy and radio power released from lightning discharges in hot giant gas planetary and brown dwarf atmospheres. The released energy determines the observability of signatures, and the effect lightning has on the local atmosphere of the object.
This work combines knowledge obtained from planetary and earth sciences and uses that to learn more about extrasolar systems. My main results show that lightning on exoplanets may be more energetic than in the Solar System, supporting the possibility of future observations and detection of lightning activity on an extrasolar body. My work provides the base for future radio, optical, and infrared search for "exo-lightning".
en
University of St Andrews
The University of St Andrews
Hodosán, G.; Helling, Ch.; Asensio-Torres, R.; Vorgul, I. & Rimmer, P. B., 2016, Monthly Notices of the Royal Astronomical Society, 461, 3927
Hodosán, G.; Rimmer, P. B. & Helling, Ch., 2016, Monthly Notices of the Royal Astronomical Society, 461, 1222
Hodosán, G., Helling, Ch., & Vorgul, I.; Submitted to the Monthly Notices of the Royal Astronomical Society (Feb. 2017)
Hodosán, G.; Rimmer, P. B. & Helling, Ch., submitted to the Conference proceedings of the 8th International Workshop on Planetary, Solar and Heliospheric Radio Emissions (PRE 8), held in Seggauberg near Leibnitz/Graz, Austria, October 25−27, 2016
Attribution-NonCommercial-NoDerivatives 4.0 International
http://creativecommons.org/licenses/by-nc-nd/4.0/
Exoplanets
Brown dwarf
Atmospheric electricity: lightning
Solar System: Earth, Venus, Jupiter, Saturn
Comparative planetology: modelling, observations
QB820.H73
Extrasolar planets
Brown dwarf stars
Atmospheric electricity
Lightning on exoplanets and brown dwarfs
Modelling and detection of lightning signatures throughout the electromagnetic spectrum
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/137532019-04-01T10:03:02Zcom_10023_126com_10023_31col_10023_129
Dunn, Malcolm H.
Sinclair, Bruce
Moseley, Richard R.
253 p.
2018-06-06T10:00:17Z
2018-06-06T10:00:17Z
1995-07
http://hdl.handle.net/10023/13753
This work contains theoretical and experimental studies of the properties of three-level atoms subjected to two single-frequency, continuous-wave laser sources with special emphasis on magnetic-field-induced sum frequency mixing (SFM) and electromagnetically-induced transparency (EIT). In sodium vapour, two resonant-enhancement routes for SFM were experimentally studied. In one route (3S-3P-3D) the output is generated on a quadrupole-allowed transition and on the other (3S-3P-4P), a dipole-allowed transition. Phase matching conditions are studied in detail. On the second route, the two contributions to the phase mismatch can combine to heavily distort the spectroscopic lineshapes observed. Doubly-resonant SFM is considered and two paths for excitation of the output coherence are identified. Control of their relative strength, via the input laser strengths, is predicted, as well as interference between them. These are both experimentally observed on the 3S1/2-3P1/2-3D3/2 transition scheme in sodium. Theory is presented to show how the use of a strong upper laser in resonant SFM can, by EIT, greatly reduce the absorption on the lower transition without similarly reducing the nonlinear process. A significant increase in conversion efficiency is predicted. Theory is also presented on the inclusion of the local field correction, which is relevant for high vapour densities, in the Bloch equations for the three-level atom. Nonlinear coherence cross-coupling terms arise and the generalised equations are then used for two case studies; one concerning EIT, the other SFM. EIT is experimentally studied using continuous-wave lasers in rubidium vapour. Focusing and de-focusing were observed on the probe laser beam as it tunes through the transparency window at close, but separate, detunings. This is attributed to the radial intensity profile of the coupling laser which imposes a spatial refractive index modulation on the medium at the probe laser wavelength.
en
University of St Andrews
The University of St Andrews
TK7871.3G3M7
Lasers
Sum frequency mixing and quantum interference in three-level atoms
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/5372019-07-01T10:11:48Zcom_10023_126com_10023_31col_10023_129
Samuel, Ifor D. W.
Hay, Ron T.
Martin, Sarah Friede
232
2008-10-21T15:31:34Z
2008-10-21T15:31:34Z
2008-06-24
http://hdl.handle.net/10023/537
This thesis presents an investigation of fluorescence resonance energy transfer (FRET) as a reporting signal for protein-protein interactions. Quantitative optical assays to measure protein binding, conjugation and deconjugation are developed and results validated by conventional biochemical techniques. The optical techniques developed provide fast, cheap, quantitative and accurate alternatives to conventional methods. Fluorescent protein fluorophores ECFP and Venus-EYFP were chosen as they are a non-interfering FRET pair and provide an inexpensive and convenient cloning-based labelling method.
The small ubiquitin-like modifier SUMO and the SUMOylation pathway leading to its conjugation to target proteins is investigated as a model system. These assays are hence particularly relevant to research on post-translational modification and ubiquitin systems. In protein-protein binding assays we utilise both steady-state and time-resolved FRET detection to measure the equilibrium binding constant of the well-characterised pair SUMO1 and Ubc9. An assay in multi-well plate format is also presented, which uniquely enables repeat measurements under varying conditions and under the addition of further substances. The multi-protein binding interactions of the SUMOylation pathway including RanBP2 are analysed in binding inhibition assays. Our results clarify the role of RanBP2: a
covalent SUMO1-Ubc9 link is required for the formation of a trimeric complex, although mutual binding sites are present on all three proteins. Furthermore, the binding of SUMO1 and Ubc9 is disrupted by RanBP2, which may be an essential step in transferring SUMO1 to its target protein. A FRET-based kinetic study of this conjugation process to RanGAP1 is presented.
An assay to monitor the deconjugation of SUMO1 by specific proteases is established using a doubly-tagged SUMO construct. This enables a quantitative analysis of protease and substrate specificity based on real-time kinetic data, a characterisation of crude cell extracts and a high-throughput screen for protease inhibitors using FRET. A screen of the National Cancer Institute (NIC) diversity set for SenP1 inhibition reveals nine suitable compounds, which are potential anti-cancer drugs.
The results of two further projects, the study of protein-protein binding by measuring small refractive index changes and the autofluorescence of normal and neoplastic cervical tissue models are also presented. In the latter, principal component analysis was used to systematically identify emission regions of
significant variation between samples, enabling discrimination between healthy
and pre-cancerous tissue models.
34301064 bytes
application/pdf
en
University of St Andrews
The University of St Andrews
Biophotonics Collaboration
Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported
http://creativecommons.org/licenses/by-nc-nd/3.0/
FRET
SUMO
Fluorescence
Energy transfer
Protein binding
TCSPC
Binding constant
Inhibition
Ubc9
RanBP2
Drug screen
SenP1
Fluorescence resonance energy transfer studies of protein interactions
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/69712019-04-01T10:03:04Zcom_10023_126com_10023_31col_10023_129
Smith, Graham Murray
Speirs, Peter James
Engineering and Physical Sciences Research Council (EPSRC)
xii, 302 p.
2015-07-13T09:13:53Z
2015-07-13T09:13:53Z
2014
uk.bl.ethos.658897
http://hdl.handle.net/10023/6971
This thesis presents the development of various methods for measuring rainfall
rates using horizontally-pointing millimetre-wave radars. This work builds from
the combination of a T-matrix scattering model that allows the scattering from
almost arbitrarily pro led rotationally symmetric particles to be calculated, and
drop shape models that allow the effects of temperature and pressure on the shape
to be taken into account.
Many hours of rain data have been collected with 38 and 94 GHz FMCW radars,
as well as with a disdrometer and weather station. These have been used to develop
single- and dual-frequency techniques for measuring rainfall rate.
A temperature, polarisation and attenuation corrected application of simple
power-law relationships between reflectivity and rainfall rate has been successfully
demonstrated at 38 GHz. However, at 94 GHz it has been found that more detailed
functions relating reflectivity, attenuation and rainfall rate are beneficial. A
reflectivity-based determination of attenuation has been adapted from the literature
and successfully applied to the 94 GHz data, improving the estimate of rainfall rate
at longer ranges.
The same method for estimating attenuation has also been used in a dualfrequency
technique based on the ratio of the extinction coefficients at 38 and 94
GHz, but with less success. However, a dual-frequency reflectivity ratio based approach
has been successfully developed and applied, producing good estimates of
rainfall rate, as well as reasonable estimates of two drop-size distribution parameters.
Simulations of radar measurements of airborne volcanic ash have also been carried
out, demonstrating that for most reasonable measurement configurations the
optimal frequencies would typically be 35 GHz or 94 GHz, not the more commonly
used 3-10 GHz. It has also been shown that various existing millimetre-wave radars
could be used to detect ash. Finally, there is a discussion of the optimal frequencies
for dual-frequency measurement of volcanic ash.
en
University of St Andrews
The University of St Andrews
QC973.5S7
Radar meteorology
Millimeter wave devices
Rain and rainfall--Measurement
Volcanic ash, tuff, etc.--Measurement
Millimetre-wave radar measurement of rain and volcanic ash
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/275132023-05-05T09:35:59Zcom_10023_126com_10023_31col_10023_129
Dholakia, Kishan
Bruce, Graham D.
Facchin, Morgan
Leverhulme Trust
Engineering and Physical Sciences Research Council (EPSRC)
161
2023-05-04T15:49:02Z
2023-05-04T15:49:02Z
2023-06-12
http://hdl.handle.net/10023/27513
https://doi.org/10.17630/sta/419
RPG-2017-197
EP/P030017/1
EP/R004854/1
Speckle patterns are grainy intensity patterns resulting from the random interference of light. They often arise from the interaction of light with systems that have a complex structure at the scale of the wavelength. As most ordinary objects have this property, speckle patterns are a somewhat universal phenomenon, although not easily observable under ordinary circumstances due to the lack of coherence of natural light. Since the invention of lasers however, the production of speckle patterns has become extremely simple, and a whole field of optics has emerged from it. Speckle patterns are an excellent tool for metrology. Where intuition says that precise control over all aspects of a setup is required, it is found that introducing some disorder can lead to very powerful techniques, with considerably simpler implementations. In this thesis, we explore new theoretical aspects of speckle patterns and develop new metrology techniques. We pay particular attention to the case of speckle patterns produced by an integrating sphere, which has only recently been used in this field of study. In this geometry, we develop a general model that predicts the amount of change in the resulting speckle, as a result of an arbitrary transformation. This model gives explicit results for various physical effects that can be solved from first principles, such as a variation in wavelength, refractive index, temperature, and position. We use this model in the context of metrology, and improve the state of the art by several orders of magnitude in the case of refractive index variations and displacement. We also explore the relationship between speckle and polarisation, and describe new mathematical techniques for the design of speckle patterns with custom properties (i.e. with maximal and minimal sensitivity to a measurand of interest) using light shaping.
en
Speckle patterns
Speckle
Metrology
Integrating spheres
Light shaping
On speckle patterns : integrating spheres, metrology, and beyond
Thesis
Doctoral
PhD Doctor of Philosophy
The University of St Andrews
2025-03-06
Thesis restricted in part in accordance with University regulations. Chapter 8 restricted until 6th March 2025
oai:research-repository.st-andrews.ac.uk:10023/146022019-04-01T10:03:05Zcom_10023_126com_10023_31col_10023_129
Armitage, Jonathan G. M.
Adie, Christopher J.
250 p.
2018-06-26T11:15:57Z
2018-06-26T11:15:57Z
1984
http://hdl.handle.net/10023/14602
Experimental apparatus to study dissipation in the saturated superfluid helium film has been developed. The low temperature parts comprise a sealed cell containing liquid helium, to which are affixed two parallel plate capacitors, functioning both as liquid reservoirs and as a way of measuring the liquid level. A small hole in a thin plastic film located in the flow path between the two capacitors forms the flow-limiting constriction. This arrangement introduces large velocity gradients in the vicinity of the hole. Film flow is initiated and sustained by an electric field in one capacitor, generated by a purpose-built Film Drive Unit (FDU) and a high-voltage amplifier. Detailed study of the helium film under steady flow conditions was not possible, but those results which were obtained indicate that the transfer rate is about 30% higher than was anticipated. By applying positive feedback to the film through the FDU, the inertial oscillations can be studied over many cycles. This new method has revealed some unexpected results, and a variety of types of oscillation behaviour have been observed. A theoretical model of dissipation has been developed, based on the premise that vortices in the film are oriented perpendicular to the film plane and are free to move and cross streamlines. According to this model, the large steady film transfer rates are due to the separation of the region of dissipation and the region of maximum velocity, an effect caused by the radial-flow geometry. Numerical simulation of the inertial oscillations using the model reproduces some of the behaviour observed experimentally, provided that the rate of vortex creation is taken to be a step function of the velocity. The shape of the liquid helium surface tension meniscus has been calculated numerically. The calculation is valid for the moving and static film in the absence of dissipation.
en
University of St Andrews
The University of St Andrews
QC183.H3A3
Dissipation in the superfluid helium film
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/143212019-04-01T10:03:06Zcom_10023_126com_10023_31col_10023_129
Dunn, Malcolm H.
Kane, D.M.
British Council
Association of Commonwealth Universities
xii, 300p.
2018-06-20T10:33:00Z
2018-06-20T10:33:00Z
1984-07
http://hdl.handle.net/10023/14321
This thesis describes the development of an intracavity frequency doubled dye laser from a commercial Spectra-Physics 380D single frequency ring dye laser, and the application of this system to a number of spectroscopic studies in discharges. Evaluation of the stability of the laser cavity is carried out, by computer calculation, in order to optimise the optical component set used in the frequency doubled dye laser. Using an ADA (ammonium dihydrogen arsenate) crystal, 17 mW of continuous wave ultra-violet, tunable over the range 292-302 nm, has been produced. The linewidth, when the laser is stabilised, is about 500 kHz in the UV. The CW UV output has been used to measure helium triplet (23S) metastable densities in a positive column discharge as a function of pressure (1-8 Torr) and current (2.5-80 mA). A maximum density of 10x10<super> 12</super> cm-3 is measured for a pressure of 2 Torr and current of 60mA. The measured metastable densities are used in a rate equation analysis to extract values of the rate coefficient for distraction (by collisions with electrons) of the 23S metastables (1.6x10<super>-8</super> cm3s-1 for p = 2 Torr). A study of the optogalvanic signal generated when irradiating a neon positive column discharge with laser light of wavelength 588.2 nm, corresponding to the ls5-2p2 transition, is carried out. The signal is found to change sign as the dye laser power is increased, for some discharge conditions. Spatial studies of the optogalvanic signal in conjunction with absorption and emission studies are carried out to investigate the evolution of the population densities of levels connected to the 1s5 and 2p2 levels. A rate equation model is developed which demonstrates the importance of the 1s3 population density in explaining the observed sign reversal. A high resolution study of two transitions in the UV, in the tungsten spectrum, is presented. The even isotope splittings and the hyperfine splitting between the two strongest hyperfine components on transitions at 294.4 nm and 294.7 nm have been resolved by saturated absorption spectroscopy. From centre of gravity considerations the hyperfine splittings of the three levels involved in the two transitions have been predicted as 1630 MHz for the7s3 level, -506 MHz for the 3692 level and 225 MHz for the 3683 level. A simple wavemeter using a corner-cube Michelson interferometer is described. Digital counting circuits to provide a direct reading of either the fundamental or second harmonic wavelength have been designed and constructed. Wavelength readings accurate to 1 part in 106 are achieved.
en
University of St Andrews
The University of St Andrews
TK7872.L3K2
Lasers
Dye lasers
Atomic laser-spectroscopy in the UV and visible
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/143462019-04-01T10:03:08Zcom_10023_126com_10023_31col_10023_129
Carson, T. R. (Thomas Richard)
Slebarski, T. B.
Papadakos, Dimitrios N.
University of St Andrews
312 p.
2018-06-20T13:37:52Z
2018-06-20T13:37:52Z
1981
http://hdl.handle.net/10023/14346
There are three principal aims of this work; firstly to derive the analytical expressions for the potential energy and the mutual gravitational attraction between two homogeneous or non-homogeneous oblate spheroids with coplanar equatorial planes; secondly, to construct and study the equations of motion of dynamical systems consisting of particles and rigid homogeneous spheroidal bodies whose equatorial planes are coplanar; thirdly, to investigate by numerical integration and compare the evolution of dynamical models of interacting galaxies. Two different types of dynamical models of galaxies were used in this work:(a) galaxies consisting of gravitating particles, (b) galaxies comprising of gravitationally interacting particles and heavy central rigid homogeneous oblate spheroids. Chapter (2) and appendices (4), (5), (6) and (7) are an account of the method used to derive the expressions for the potential energy and the mutual gravitational attraction between two rigid bodies bounded by spheroidal surfaces with coplanar equatorial planes, when the densities of the bodj.es are either constant or inversely proportional to the square of the radial distance from the centres of the bodies. These expressions were at first obtained in the form of non-elementary integrals over the complete elliptic integrals of the first and second kind, a result due to the fact that the common volume between two ellipsoids cannot be expressed in finite terms. The evaluation of these integrals was achieved with the aid of MacLaurin' s theorem by collapsing one of the spheroids to its confocal disc; their final form is that of rapidly convergent series in terms of the parameters which determine the shape and orientation of the spheroids. In the course of obtaining the expressions mentioned above we derived some other useful formulae, for example, the formulae giving the gravitational attraction between two homoeoids and the potential and force law of a non-homogeneous oblate spheroid. Having found the expressions for the gravitational potential and attraction between two spheroids we proceeded by constructing and solving the equations of motion of dynamical systems consisting of either particles or particles and rigid homogeneous oblate spheroids with coplanar equatorial planes [chapters (1) and (3), appendices (2) and (3)]. The solutions of the equations of motion - being non-algebraic - were obtained in the form of power series. In particular, for the first type of dynamical systems (particles only) they were found in the form of three different types of series. The first type is based on the development and implementation of generalized f and g series for the N-body problem, the second type is based on recurrent formulae used for the evaluation of the terms of the series and the last type of series is a power series in terms of ln ɼijτ/ɼij and polynomial of ɼijτ/ɼij. All the series mentioned above lend themselves easily, to numerical calculations since their convergence, which was analytically proved, is a rapid one. We concluded the present work by numerically integrating the equations of motion of dynamical models of pairs of interacting galaxies. The galaxies were of the types (a) and (b) mentioned previously. The numerical integration was performed with variable time steps in order to reduce computing time. A general method was developed for the precise evaluation of the length of the time step determined by the desired integration accuracy. The calculations were carried out to an extremely high degree of accuracy. The most significant of the results of the numerical experiments on the evolution of dynamical models of interacting galaxies were:(i) the development of long-lived spiral structure when galaxies of type (b) were lased even for intrinsic velocities and impact parameters so high that galaxies of type (a) were unable to produce such structure,(ii) the roughly periodic appearance and disappearance of the spiral structure,(iii) the fact that in the early stages of their evolution the dynamical models take up rather long-lived triaxial ellipsoidal shapes.
en
University of St Andrews
The University of St Andrews
St Andrews University Observatory
QB807.P2
Astrometry
Dynamics and kinematics of systems consisting of spherical and spheroidal bodies
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/184882023-08-21T13:11:48Zcom_10023_126com_10023_31col_10023_129
Lovett, Janet Eleanor
Shah, Anokhi
Engineering and Physical Sciences Research Council (EPSRC)
xxvi, 195, [3] p.
2019-09-17T13:35:23Z
2019-09-17T13:35:23Z
2019-12-03
http://hdl.handle.net/10023/18488
Electron paramagnetic resonance spectroscopy is a versatile tool for probing structural information about systems with unpaired electrons, in particular, biological systems with metal centres or chemically attached spin labels. This work uses a variety of electron paramagnetic resonance techniques to investigate the ability to measure distances between two spins (radical and metal), as well as characterise the local environment. Distance measurements are used to probe the mechanism of translocation across a membrane, where a change in distance is observed upon ATP cycling, indicating channel movement of the SecYEG:SecA complex. Furthermore, to expand the scope of distance measurements for more complex, cysteine-rich systems, spin labelling regimes are developed and optimised on the test protein myoglobin. Specifically, next generation maleimide spin labels are demonstrated to label and selectively cleave. Myoglobin is further exploited to successfully introduce the unnatural amino acid, dehydroalanine, for selective and orthogonal labelling. The development of the labelling and measurement strategy for the gadolinium-based spin label, [Gd.sTPATCN]-SL, is also shown, where the narrow central transition of the label allows a long phase memory time and increased DEER modulation depth, to give increased measurement sensitivity. In addition, gadolinium(III) distances are used to characterise the binding site of a peptide system for the application of magnetic resonance imaging. The optimisation of measuring inter-gadolinium(III) distances between 2-5 nm at both Q- and W-band is also demonstrated in the corresponding peptide ruler series. The additional benefit of the peptide to act as a metal ruler is further investigated using copper(II), where hyperfine spectroscopy is utilised to successfully confirm the nature of the binding site as all oxygen binding.
"This work was supported by the Engineering and Physical Sciences Research
Council [grant number EP/M508214/1]" -- Acknowledgements
en
University of St Andrews
The University of St Andrews
Expanding the scope of EPR for structural studies of proteins and peptides (Thesis data) Shah, A., University of St Andrews. DOI: https://doi.org/10.17630/4bc143fb-ff43-4d1c-8c52-60d2e112a860
https://doi.org/10.17630/4bc143fb-ff43-4d1c-8c52-60d2e112a860
Electron paramagnetic resonance
EPR
Mass spectrometry
Spin labelling
New labels
Structural biology
Metals
Copper
Gadolinium
Membrane protein
Protein
Peptide
Distances
DEER
QC763.S5
Electron paramagnetic resonance
Electron paramagnetic resonance spectroscopy
Molecular biology
Molecular structure
Expanding the scope of electron paramagnetic resonance spectroscopy for structural studies of proteins and peptides
Thesis
Doctoral
PhD Doctor of Philosophy
2024-09-13
Thesis restricted in accordance with University regulations. Electronic copy restricted until 13th September 2024.
oai:research-repository.st-andrews.ac.uk:10023/217602021-04-03T02:01:41Zcom_10023_126com_10023_31col_10023_129
Sibbett, Wilson
Birkin, David J. L.
236 p.
2021-04-02T07:04:34Z
2021-04-02T07:04:34Z
2002-02-08
http://hdl.handle.net/10023/21760
https://doi.org/10.17630/sta/49
This thesis is concerned with the development of a compact diode laser source
of picosecond optical pulses having enhanced average powers. This is realised
by the application of a large amplitude sinusoidal modulation to a single-contact,
single-mode, narrow stripe, InGaAs/GaAs ridge-waveguide diode laser. The
operational characteristics of the device when in continuous wave and gain-
switched regimes are presented.
In the gain-switched regime, a minimum pulse duration of 30ps is
demonstrated, at average and peak powers up to ≈150mW and ≈1.8mW
respectively. A sonogram technique is employed to determine the sign and
magnitude of the frequency chirp in the optical pulses. On the basis of this
information aperiodic gratings are designed and fabricated in germanosilicate
optical fibres and lithium niobate crystals to realise temporal pulse compression
and efficient second harmonic generation respectively.
The effect of self-injection optical feedback is described, along with the
corresponding realisation in the reduction in the spectral bandwidth of the
optical pulses from ≈11nm to 0.05nm. When the optical feedback is provided
by a standard diffraction grating, a tuning range of 70nm is demonstrated. The
addition of a second grating results in two independently tunable outputs, with
an adjustable spectral separation of up to 53nm.
Bragg gratings are fabricated in the cores of photosensitive germanosilicate
optical fibres. It is demonstrated that when such a fibre is used in an external
cavity configuration, both temporal and spectral compression of the optical
pulses is observed.
Direct frequency conversion of the diode laser output by using quasi-phase
matched crystals of lithium niobate and KTP is demonstrated. High efficiencies
are obtained with a KTP crystal containing a waveguide structure and a Bragg
grating section to provide optical feedback to the diode laser. By this approach
impressively high average second harmonic powers of up to 7.3mW in the blue
spectral region are achieved for this frequency-doubled picosecond diode laser.
en
University of St Andrews
The University of St Andrews
Generation and characterisation of ultrashort diode laser pulses
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/146152019-04-01T10:03:08Zcom_10023_126com_10023_31col_10023_129
Rushworth, F. A.
Lawrenson, Ian J.
106 p.
2018-06-26T13:17:49Z
2018-06-26T13:17:49Z
1958
http://hdl.handle.net/10023/14615
The nuclear resonance absorption spectrum of several hydrocarbons has been studied at temperatures down to 20°K, using the bridge method of detection. A special cryostat was constructed for use with liquid hydrogen. In the case of cyclopentene, experimental evidence has been found in favour of a non-planar molecule, rotating about an axis perpendicular to the plane defined by four of the carbon atoms. This motion starts near 87°k, the temperature of the reported specific heat transition. At 124°k, the molecules appear to diffuse through the lattice, so that at 128°k, 10° below the melting point, the line width is less than the field inhomogeneity. Measurements of the second moments of n-pentane, n-hexane and n-octane indicate reorientation of the methyl groups about the end C-C axes, even at 20°K. an approximate value for the height of the barrier restricting the rotation in the n-octane molecule has been determined from the spin-lattice relaxation time measurements. Second moment measurements on cyclooctatetraeene have provided strong evidence in favour of a "tub" (D2a) structure of the molecule, with conjugated double and single bonds.
en
University of St Andrews
The University of St Andrews
Nuclear magnetic resonance in some hydrocarbons at low temperatures
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/185572021-03-30T15:23:16Zcom_10023_126com_10023_31col_10023_129
Di Falco, Andrea
Fleming, Adam Colin
Engineering and Physical Sciences Research Council (EPSRC)
xi, 121 p.
2019-09-25T11:17:56Z
2019-09-25T11:17:56Z
2019-12-03
http://hdl.handle.net/10023/18557
https://doi.org/10.17630/10023-18557
Scattering media have traditionally been seen as a hindrance to the controlled transport of
light through media, creating the familiar speckle pattern. However such matter does not cause
the loss of information but instead performs a highly complex deterministic operation on the
incoming flux. Through sculpting the properties of the incoming wavefront, we can unlock the
hidden characteristics of these media, affording us far more degrees of freedom than that which is
available to us in traditional ballistic optics.
These additional degrees of freedom have allowed for the creation of compact sophisticated
optical devices based only on the deterministic nature of light scattering. Such devices include
diffraction-limit-beating lenses, polarimeters, spectrometers, and some which can transmit entire
images through a scattering substance.
Additional degrees of freedom would allow for the creation of even more powerful devices,
in new working regimes. In particular, the application of related techniques where the scattering
material is actively modified is limited.
This thesis is concerned with the use of optothermal nonlinearity in random media as a way to
provide an additional degree of control over light which scatters through it. Specifically, we are
concerned with silica aerogel as a platform for this study.
Silica aerogel is a lightweight skeletal structure of silica fibrils, which results in a material which
is up to 99.98 % by volume. This material exhibits a unique cocktail of properties of use such as near
unitary refractive index, an order of magnitude lower thermal conductivity, and high optothermal
nonlinearity. The latter two of these properties allow for the creation of localised steep thermal
gradients, proportionally affecting the low refractive index significantly. Additionally through
differing fabrication steps, the opacity, and as a result, we can adjust the scattering strength.
In line with the development of light deterministic light scattering techniques in linear media,
we develop through the use of pump-probe setups, a framework for the development of a similar
line of techniques in nonlinear scattering media. We show that we can reversibly control the
far-field propagation of light in weakly scattering silica aerogel. Following this, we show that
nonlinear perturbation can be used to extend and modify the optical memory effect, where slight
adjustments in scattering direction maintain the overall correlation of the scattered profile. Finally,
we measure the nonlinear transmission matrix, a complete description of how any wavefront would
pass through at a particular point in a scattering media, and how that scattering can be modified
through the application of an optothermal nonlinearity.
Extending the tool of scattering media into the nonlinear regime helps pave the way toward the
next set of advances in the field of light scattering control.
"This work was supported by the Engineering and Physical Sciences Research Council [grant number
EP/M508214/1]" -- Funding
en
University of St Andrews
The University of St Andrews
Linear and nonlinear optical properties of silica aerogel (Thesis data) Fleming, A., University of St Andrews, 9 August 2019. DOI: https://doi.org/10.17630/906a13bf-413d-472e-b479-15e50b441994
https://doi.org/10.17630/906a13bf-413d-472e-b479-15e50b441994
Light scattering
Nonlinear
Transmission matrix
QC427.4F6
Light--Scattering
Nonlinear optics
Aerogels
Linear and nonlinear optical properties of silica aerogel
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/41812019-04-01T10:03:10Zcom_10023_126com_10023_31col_10023_129
Cameron, A. C.
Brown, David John Alexander
250
2013-11-08T16:48:52Z
2013-11-08T16:48:52Z
2013-11-29
http://hdl.handle.net/10023/4181
Thanks to a range of discovery methods that are sensitive to different regions of parameter space, we now know of over 900 planets in over 700 planetary systems. This large population has allowed exoplanetary scientists to move away from a focus on simple discovery, and towards efforts to study the bigger pictures of planetary system formation and evolution.
The interactions between planets and their host stars have proven to be varied in both mechanisms and scope. In particular, tidal interactions seem to affect both the physical and dynamical properties of planetary systems, but characterising the broader implications of this has proven challenging. In this thesis I present work that investigates different aspects of tidal interactions, in order to uncover the scope of their influence of planetary system evolution.
I compare two different age calculation methods using a large sample of exoplanet and brown dwarf host stars, and find a tendency for stellar model fitting to supply older age estimates than gyrochronology, the evaluation of a star's age through its rotation (Barnes 2007). Investigating possible sources of this discrepancy suggests that angular momentum exchange through the action of tidal forces might be the cause.
I then select two systems from my sample, and investigate the effect of tidal interactions on their planetary orbits and stellar spin using a forward integration scheme. By fitting the resulting evolutionary tracks to the observed eccentricity, semi-major axis and stellar rotation rate, and to the stellar age derived from isochronal fitting, I am able to place constraints on tidal dissipation in these systems. I find that the majority of evolutionary histories consistent with my results imply that the stars have been spun up through tidal interactions as the planets spiral towards their Roche limits.
I also consider the influence of tidal interactions on the alignment between planetary orbits and stellar spin, presenting new measurements of the projected spin-orbit alignment angle, λ, for six hot Jupiters. I consider my results in the context of the full ensemble of measurements, and find that they support a previously identified trend in alignment angle with tidal timescale, implying that tidal realignment might be responsible for patterns observed in the λ distribution.
en
University of St Andrews
The University of St Andrews
Brown, D. J. A. et al. (2011), Monthly Notices of the Royal Astronomical Society, Issue 415, pp. 605-618
Brown, D. J. A. et al. (2012), Monthly Notices of the Royal Astronomical Society, Issue 423, pp. 1503-1520
Brown, D. J. A. et al. (2012), Astrophysical Journal, Issue 760, pp. 139
Exoplanets
Extra-solar planets
Planetary systems
Tidal interactions
Radial velocities
Stars
Stellar ages
Gyrochronology
QB603.O74B8
Extrasolar planets
Planets--Origin
Planets--Motion
Tides
Stars--Age
Stars--Rotation
The effects of tidal interactions on the properties and evolution of hot-Jupiter planetary systems.
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/117402019-04-01T10:03:12Zcom_10023_126com_10023_31col_10023_129
Helling, Christiane
Lee, Graham Kim Huat
European Research Council (ERC)
[xii], 139, [7] p.
2017-09-25T15:23:49Z
2017-09-25T15:23:49Z
2017-12-07
uk.bl.ethos.722988
http://hdl.handle.net/10023/11740
The atmospheres of exoplanets are being characterised in increasing detail by observational facilities and will be examined with even greater clarity with upcoming space based missions such as the James Webb Space Telescope (JWST) and the Wide Field InfraRed Survey Telescope (WFIRST). A major component of exoplanet atmospheres is the presence of cloud particles which produce characteristic observational signatures in transit spectra and influence the geometric albedo of exoplanets. Despite a decade of observational evidence, the formation, dynamics and radiative-transport of exoplanet atmospheric cloud particles remains an open question in the exoplanet community.
In this thesis, we investigate the kinetic chemistry of cloud formation in hot Jupiter exoplanets, their effect on the atmospheric dynamics and observable properties. We use a static 1D cloud formation code to investigate the cloud formation properties of the hot Jupiter HD 189733b. We couple a time-dependent kinetic cloud formation to a 3D radiative-hydrodynamic simulation of the atmosphere of HD 189733b and investigate the dynamical properties of cloud particles in the atmosphere. We develop a 3D multiple-scattering Monte Carlo radiative-transfer code to post-process the results of the cloudy HD 189733b RHD simulation and compare the results to observational results.
We find that the cloud structures of the hot Jupiter HD 189733b are likely to be highly inhomogeneous, with differences in cloud particle sizes, number density and composition with longitude, latitude and depth. Cloud structures are most divergent between the dayside and nightside faces of the planet due to the instability of silicate materials on the hotter dayside.
We find that the HD 189733b simulation in post-processing is consistent with geometric albedo observations of the planet.
Due to the scattering properties of the cloud particles we predict that HD 189733b will be brighter in the upcoming space missions CHaracterising ExOPlanet Satellite (CHEOPS) bandpass compared to the Transiting Exoplanet Space Survey (TESS) bandpass.
en
University of St Andrews
The University of St Andrews
Attribution-NonCommercial-NoDerivatives 4.0 International
http://creativecommons.org/licenses/by-nc-nd/4.0/
Exoplanets
Atmospheres
Radiative-transfer
Cloud formation
Hot Jupiters
HD 189733b
Monte Carlo radiative-transfer
Global circulation models
QB820.L4
Extrasolar planets--Atmospheres--Mathematical models
Cloud physics--Mathematical models
Radiative transfer
Glass rain : modelling the formation, dynamics and radiative-transport of cloud particles in hot Jupiter exoplanet atmospheres
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/89692019-04-01T10:03:12Zcom_10023_126com_10023_31col_10023_129
Korolkova, Natalia
Croal, Callum
148
2016-06-13T15:24:46Z
2016-06-13T15:24:46Z
2016-11-30
uk.bl.ethos.687029
http://hdl.handle.net/10023/8969
This thesis studies continuous variable mixed states with the aim of better understanding the fundamental behaviour of quantum correlations in such states, as well as searching for applications of these correlations. I first investigate the interesting phenomenon of discord increase under local loss and explain the behaviour by considering the non-orthogonality of quantum states. I then explore the counter-intuitive result where entanglement can be created by a passive optical beamsplitter, even if the input states are classical, as long as the input states are part of a larger globally nonclassical system. This result emphasises the importance of global correlations in a quantum state, and I propose an application of this protocol in the form of quantum dense coding.
Finally, I develop a quantum digital signature protocol that can be described entirely using the continuous variable formalism. Quantum digital signatures provide a method to ensure the integrity and provenance of a message using quantum states. They follow a similar method to quantum key distribution (QKD), but require less post-processing, which means they can sometimes be implemented over channels that are inappropriate for QKD. The method I propose uses homodyne measurement to verify the signature, unlike previous protocols that use single photon detection. The single photon detection of previous methods is designed to give unambiguous results about the signature, but this comes at the cost of getting no information much of the time. Using homodyne detection has the advantage of giving results all the time, but this means that measurement results always have some ambiguity. I show that, even with this ambiguity, the signature protocol based on homodyne measurement outperforms previous protocols, with the advantage enhanced when technical considerations are included. Therefore this represents an interesting new direction in the search for a practical quantum digital signature scheme.
en
University of St Andrews
The University of St Andrews
Attribution-NonCommercial-NoDerivatives 4.0 International
http://creativecommons.org/licenses/by-nc-nd/4.0/
Quantum information
Quantum digital signatures
Quantum discord
Quantum optics
QC174.17E58C8
Quantum entanglement
Digital signatures
Quantum optics
Quantum correlations in continuous variable mixed states : from discord to signatures
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/213612021-08-14T13:27:35Zcom_10023_126com_10023_31col_10023_129
Korolkova, Natalia
Thornton, Matthew
Engineering and Physical Sciences Research Council (EPSRC)
xvi, 259 p.
2021-02-03T07:00:34Z
2021-02-03T07:00:34Z
2020-12-01
http://hdl.handle.net/10023/21361
https://doi.org/10.17630/sta/20
1798331
In the first half of this Thesis, we introduce a framework of “quantum
cryptographic agility,” which allows for a resource-efficient swap of an
underlying cryptographic protocol. Specifically, we introduce several
schemes which perform the tasks of Digital Signatures and Secret
Sharing. Our first achievement is an investigation of Quantum Digital
Signatures (QDS) over a continuous-variables platform, consisting
of phase-encoded coherent states and heterodyne phase detection.
QDS allows for secure authentication of a classical message, while
guaranteeing message transferability. For the first time, we prove
security of CV QDS in the presence of an eavesdropper on the quantum
channels.
We then introduce a continuous variable (CV) Quantum Secret
Sharing (QSS) protocol. Our security proof allows for classical information
to be split and shared between multiple potentially dishonest
recipients, while retaining security against collective beamsplitter and
entangling-cloner attacks. In the last chapter of this half, we introduce
another QDS scheme which runs over identical hardware setup to
our QSS protocol. We analyse experimental data in which quantum
coherent states were distributed at a rate of 1 GHz, which for QDS
allows us to securely sign a message in less than 0.05 ms.
In the second half of this Thesis we suggest and discuss a deterministic
source of nonclassical light, which we call “PhoG”. Our source is
based on the coherent diffusive photonics, relying on both coherent
and dissipative evolution of the quantum state, and may be realised
in an array of dissipatively-coupled laser-inscribed waveguides in a χ⁽³⁾
glass. We analyse the PhoG device with several analytical and
numerical models and demonstrate that a coherent state input leads
to a bright output state with strong photon-number squeezing. With
minor reconfiguration our system can generate entanglement between
spatially separated modes via a process analogous to four-wave
mixing.
en
University of St Andrews
The University of St Andrews
Agile quantum cryptography and non-classical state generation (thesis data) Thornton, M., University of St Andrews, 2020. DOI: https://doi.org/10.17630/6ba10862-4bdd-478f-8bd7-4f4b4d383374
https://doi.org/10.17630/6ba10862-4bdd-478f-8bd7-4f4b4d383374
Cryptography
Quantum theory
Agile quantum cryptography and non-classical state generation
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/9092019-04-01T10:03:13Zcom_10023_126com_10023_31col_10023_129
Dholakia, Kishan
Tsampoula, Xanthi
200
2010-06-11T11:50:02Z
2010-06-11T11:50:02Z
2009-11-30
http://hdl.handle.net/10023/909
In this thesis, femtosecond (fs) cellular transfection of Chinese Hamster Ovary (CHO)
cells was performed using a tightly focused Gaussian beam. The beam focus was
positioned on the cell membrane and three laser doses, each of 40 ms duration, were
delivered allowing for the formation of a highly localized pore on the cell membrane. The
membrane pore, induced as a result of a multiphoton process known as photoporation,
permitted the surrounding DNA to diffuse into the cell cytoplasm. 48 hours after laser
irradiation, the viable photoporated cells expressed a red fluorescent protein. The
topography of a photoporated cell, targeted with tightly focused fs pulses, was also
monitored as a function of the input power using Atomic Force Microscopy. Following
this, I generated and implemented a “non-diffracting” quasi-Bessel beam (BB) by means
of a conical shaped lens, the axicon, which successfully provided an alternative route for
photoporation to the highly divergent Gaussian beam. A comparison was given between
the two beam approaches for photoporation. The “non-diffracting” character of the BB
resulted in the first successful attempt towards automating optical transfection. This was
achieved by using an axicon and a spatial light modulator (SLM) to provide phase
modulation on the annular spatial spectrum field of the BB. This approach provided
control over the lateral and axial position of the beam with respect to the cell membrane,
allowing for point and click photoporation. Successful photoporation of CHO cells was
also demonstrated using for the first time an axicon tipped optical fibre. The applicability
prospects of this method are significant, ranging from potential endoscopic embodiments
of the technique to advanced studies of tissue properties in vitro and in vivo.
en
University of St Andrews
The University of St Andrews
Lasers in cytology
Beam optics
Femtosecond lasers
Femtosecond cellular transfection using novel laser beam geometries
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/117802021-08-18T02:01:48Zcom_10023_126com_10023_31col_10023_129
Koenig, Friedrich Ernst Wilhelm
Jacquet, Maxime J.
Engineering and Physical Sciences Research Council (EPSRC)
University of St Andrews. 600th Anniversary Scholarship
191, xxxii p.
2017-10-02T10:56:51Z
2017-10-02T10:56:51Z
2017-12-07
http://hdl.handle.net/10023/11780
This thesis considers the problem of calculating and observing the mixing of modes of positive and negative frequency in inhomogeneous, dispersive media. Scattering of vacuum modes of the electromagnetic field at a moving interface in the refractive index of a dielectric medium is discussed. Kinematics arguments are used to demonstrate that this interface may, in a regime of linear dispersion, act as the analogue of the event horizon of a black hole to modes of the field. Furthermore, a study of the dispersion of the dielectric shows that five distinct configurations of modes of the inhomogeneous medium at the interface exist as a function of frequency. Thus it is shown that the interface is simultaneously a black- and white-hole horizon-like and horizonless emitter. The role, and importance, of negative-frequency modes of the field in mode conversion at the horizon is established and yields a calculation of the spontaneous photonic flux at the interface. An algorithm to calculate the scattering of vacuum modes at the interface is introduced. Spectra of the photonic flux in the moving and laboratory frame, for all modes and all realisable increase in the refractive index at the interface are computed. As a result of the various mode configurations, the spectra are highly structured in intervals with black-hole, white-hole and no horizon. The spectra are dominated by a negative-frequency mode, which is the partner in any Hawking-type emission. An experiment in which an incoming positive-frequency wave is populated with photons is assembled to observe the transfer of energy to outgoing waves of positive and negative frequency at the horizon. The effect of mode conversion at the interface is clearly shown to be a feature of horizon physics. This is a classical version of the quantum experiment that aims at validating the mechanism of Hawking radiation.
en
University of St Andrews
The University of St Andrews
Attribution-NonCommercial-NoDerivatives 4.0 International
http://creativecommons.org/licenses/by-nc-nd/4.0/
Hawking radiation
Quantum field theory
Quantum field theory in curved spacetime
General relativity
Event horizon
Black hole
Fibre optics
Nonlinear optics
Nonlinear fibre optics
Mathematical physics
Experimental physics
Optical horizon
Spontaneous emission of light from the vacuum
Stimulated emission
Quantum physics
Quantum electrodynamics
Experimental quantum field physics
Unruh
Few-cycle laser pulses
QC174.52V33J2
Quantum field theory
Quantum electrodynamics
Nonlinear optics
Fiber optics
Negative frequency at the horizon : scattering of light at a refractive index front
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/292002024-02-14T12:02:10Zcom_10023_126com_10023_31col_10023_129
Keeling, Jonathan Mark James
Staffini, Maria Laura
Engineering and Physical Sciences Research Council (EPSRC)
University of St Andrews
181
2024-02-09T11:42:07Z
2024-02-09T11:42:07Z
2020-07-27
https://hdl.handle.net/10023/29200
https://doi.org/10.17630/sta/742
EP/M506631/1
The realisation of self-organisation of ultracold atoms in optical cavities, where the light field can couple strongly to the atomic field, paves the way for the observation of phase transitions in which the spatial order is entirely emergent, such as glassiness or supersolidity. This fact, and the flexibility of cavity environment, makes these light-matter systems ideal candidates for quantum simulation. A wide range of physics has already been demonstrated in cavities coupled to ultracold atoms.
In this work, we seek to contribute two additions to the growing toolbox of phase transitions in optical cavities. First, we consider a transversely pumped, single mode cavity containing a Bose-condensed atomic cloud – a system that is well studied, and which undergoes spatial self-organisation. We treat this in an open system formalism, without the two-level approximation or linearised treatment which are common assumptions in literature. Within this complete treatment, we observe a first order phase transition, with associated bistability leading to hysteresis. We also demonstrate that in some parameter range, the system displays chaotic behaviour due to a strange attractor of the dynamics. Both of these observations explain features of experimental data from previous literature.
We then consider the case of a multimode, longitudinally pumped cavity in the confocal geometry, i.e. supporting a degenerate mode family. This is motivated both by the rich physics observed in a multimode confocal cavity in the transversely pumped regime, and by the self-patterning observed in single-mirror experiments. We find that the behaviour of the system is too complex for characterisation, and that the analytic understanding we can gain from weak coupling approximations never holds. We conclude that there is no simple self-organisation in our model.
en
University of St Andrews
The University of St Andrews
QC446.2S82
Quantum optics
Atoms
Low temperatures
Self-organisation of cold atoms in optical cavities
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/1472019-07-01T10:09:57Zcom_10023_126com_10023_31col_10023_129
Krauss, Thomas F.
Neale, Steven Leonard
v, 168 p.
2007-01-09T16:59:03Z
2007-01-09T16:59:03Z
2007
http://hdl.handle.net/10023/147
Three projects are described in this thesis that combine microfabrication techniques with optical micromanipulation. The aim of these projects is to use expertise in microlithography and optical tweezing to create new tools for Lab-on-Chip devices. The first project looks at the creation of microgears that can be moved using an optical force. The microgears include one dimensional photonic crystal that creates birefringence. This allows the transfer of angular momentum from a circularly polarised light beam to the microgear, making them spin. The microgears are simulated, fabricated and tested. Possible biological applications are suggested. The second project looks at creating microchannels to perform micromanipulation experiments in. Different methods of fabricating the microfluidic channels are compared, and the resulting chambers are used to find the maximum flow rate an optical sorting experiment can be performed at. The third project involves using a thin photoconductive layer to allow the optical control of an electrical force called dielectrophoresis. This light induced dielectrophoresis (LIDEP) allows similar control to optical tweezing but requires less irradiance than optical tweezing, allowing control over a larger area with the same input optical power. A LIDEP device is created and experiments to measure the electrical trap size that is created with a given optical spot size are performed. These three projects show different microfabrication techniques, and highlight how well suited they are for use in optical manipulation and microfluidic experiments. As the size of objects that can be optically manipulated matches well with the size of objects that can be created with microfabrication, it seems likely that many more interesting applications will develop.
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University of St Andrews
The University of St Andrews
Creative Commons Attribution-NonCommercial-NoDerivs 2.5 Generic
http://creativecommons.org/licenses/by-nc-nd/2.5/
QC689.5L35N4
Microfabrication
Micrurgy
Laser beams
Microlithography
Microfluidics
Optics
Optically controlled microfluidics
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/1422019-07-01T10:11:05Zcom_10023_126com_10023_31col_10023_129
Dholakia, Kishan
Shah, Anjali
xi, 187 leaves
2006-11-21T18:31:26Z
2006-11-21T18:31:26Z
2006-05
http://hdl.handle.net/10023/142
Semiconductor diode lasers are successful tools in atomic spectroscopy. They are routinely used in frequency conversion applications to develop devices that access regions of the spectrum not directly available. This thesis describes the practical application of novel violet diode laser systems and their possible inclusion in spectroscopic systems.
The design, assembly and successful operation of a doubly resonant optical parametric oscillator is described. There is discussion of the spectral behaviour of the device and the potential for pumping with a violet diode laser. Methods to adapt the output from the solitary diode devices are demonstrated with the use of microlensed diode lasers and extended cavity configurations. Details of the current tuning, linewidth and
smooth tuning characteristics of a number of the lasers used are given. A commercial
violet diode laser is used within an extended cavity to measure the hyperfine structure
of atomic indium from a hollow cathode galvatron source at room temperature.
Stabilisation of the diode laser to a line from the indium spectrum is attempted.
The remainder of the thesis is concerned with the development of techniques to deliver
clearer and more precise spectral information about trace species. Microlensed
red and violet diode lasers are used to generate light at 254nm via sum frequency
generation for the direct detection and modulation spectroscopy of mercury vapour,
with microlensed lasers with modulation allowing more accurate discrimination between
spectral features than direct absorption measurements. In addition Raman
tweezers modulation spectroscopy is undertaken to investigate polymer microspheres
and biological cell samples where the use of the modulation technique demonstrated
improvements in the acquisition time and clarity of spectra through increased signal
to noise and rejection of background fluorescence effects. A comparison between the
direct and modulation techniques for all the systems indicates the greater sensitivity
of the modulation technique.
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en
University of St Andrews
The University of St Andrews
Creative Commons Attribution-NonCommercial-NoDerivs 2.5 Generic
http://creativecommons.org/licenses/by-nc-nd/2.5/
Semiconductor diode lasers
Atomic spectroscopy
Violet diode laser systems
Spectroscopic systems
TA1700.S5
Nonlinear optics
Atomic spectroscopy
External cavity diode lasers and non-linear optical frequency conversion in spectroscopic applications
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/148852019-04-01T10:03:17Zcom_10023_126com_10023_31col_10023_129
Reid, Derryck T.
229 p.
2018-07-04T08:48:40Z
2018-07-04T08:48:40Z
1995-07
http://hdl.handle.net/10023/14885
The work presented in this thesis describes the design, configuration and operation of femtosecond optical parametric oscillators based on the materials KTiOPO4 (KTP) and RbTiOAsO4 (RTA) and pumped by a self- modelocked Ti:sapphire laser. The alignment of the pump laser is detailed and thermal effects in the Ti:sapphire rod are examined in the context of a general technique which optimises modelocked performance at any pump power. A KTP-based femtosecond parametric oscillator is described which produces 400-fs-duration signal pulses at an average output power of 150 mW when operated in the absence of group-velocity dispersion- compensation. With intracavity dispersion-compensation, the oscillator produces 40-fs-duration pulses with an average power of 50 mW. Tuning is demonstrated from 1.12 - 1.25 mum in the signal wave and from 2.5 - 3.0 mum in the idler wave by changing only the pump-laser wavelength. Using a novel idler-feedback arrangement, reductions in the oscillation threshold and increases in the signal output power of 10 % are described. Soliton generation in the oscillator is achieved when the net cavity dispersion is positive and results show good agreement with theory. An oscillator using RTA is demonstrated which achieves conversion efficiencies exceeding 30 % and has an operating threshold of only 50 mW. Average signal powers of 100 mW and 185 mW are extracted from the oscillators with and without dispersion-compensation respectively. The corresponding pulse durations are 67 fs and 980 fs and tunability in the signal and idler waves from 1.23 - 1.34 mum and 2.10 - 2.43 mum is demonstrated. Visible output from 620 - 660 nm is obtained by intracavity- doubling and powers of up to 170 mW are measured. These results suggest that RTA has a higher nonlinear coefficient than KTP.
en
University of St Andrews
The University of St Andrews
TK7872.O3R3
Oscillators
Optical parametric oscillators
Novel nonlinear techniques for femtosecond pulse generation in the visible and near-infrared
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/143042019-04-01T10:03:18Zcom_10023_126com_10023_31col_10023_129
Carson, T. R. (Thomas Richard)
Jeffery, C. Simon
Science and Engineering Research Council (SERC)
183, 29p.
2018-06-20T09:31:17Z
2018-06-20T09:31:17Z
1983
http://hdl.handle.net/10023/14304
We investigate stellar models for main-sequence and horizontal-branch stars constructed using the Carson opacities and make comparisons with models based on the Cox-Stewart opacities. A Henyey code based on the prescription of Kippenhahn et al (1967) is used for most of the calculations of stellar structure and evolution. In the equation of state we treat ionisation equilibrium and non-relativistic degeneracy for separate temperature-density regimes. The opacity is obtained by 4-dimensional linear interpolation in the Carson opacity tables. Nuclear energy generation rates are taken from Fowler et al (1975) and neutrino losses from the approximation due to Beaudet et al (1967). Electron-screening factors are from Reeves (1965). The standard local mixing-length theory of Bohm-Vitense (1958) is used to treat non-adiabatic convection, although some models are calculated with modifications due to Deupree et al (1979, 1980). We neglect semi convection. The Carson opacities have only a small effect on the position of ZAHB models, but this may be metallicity dependent. The drop in the hydrogen- shell luminosity due to the helium-core expansion during HB evolution is greater than that obtained with the Cox-Stewart opacities. Allowing for the inclusion of semi convection and convective overshooting, we find that adoption of the Carson opacities leads to a reduction of approximately 25% in the HB lifetimes. For a given range of values for the masses and envelope helium abundances of stars on a synthetic HB, the width in effective temperature is increased, and in luminosity the width is decreased. The dependence of the core luminosity on the falling core helium abundance is increased by approximately 16%. Studies of main-sequence stars lead to agreement with Stothers' (1974a, 1974b, 1976) results for homogeneous models constructed with the Carson opacities. The evolution of main-sequence stars of intermediate mass is unaffected by the change in the opacity. Two evolutionary sequences (for 1 Mo stars) suggest that the main-sequence lifetimes of low mass stars may be reduced by as much as 30%. Combined with a shift in the ZAMS position this will move isochrones for low mass stars towards lower effective temperatures and densities. If studies of red-giant evolution indicate little change in the luminosity level of the horizontal branch, globular cluster ages determined from the position of the main-sequence turnoff point may be substantially reduced (possibly by as much as 50%). This could save a conflict between observed values for globular cluster ages and a value for the Hubble constant of 90. Studies of the apsidal motion constant, k₂, for evolved MS stars shows that the discrepancy between observed values of k₁ for eclipsing binary systems and theoretical values obtained from homogeneous stellar models may be resolved by considering the evolution of the binary components. CO Lac is an exception to this result, but analysis of the observations suggests that a redetermination of the orbital semi-amplitudes may resolve the conflict.
en
University of St Andrews
The University of St Andrews
University of St Andrews Observatory
QB806.J4
Stars--Evolution
Studies in stellar structure and evolution
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/27012019-04-01T10:03:19Zcom_10023_126com_10023_31col_10023_129
Roberts, Bernard
Edwin, Patricia Mary
346
2012-06-08T13:49:07Z
2012-06-08T13:49:07Z
1985
http://hdl.handle.net/10023/2701
The effect of structuring, in the form of magnetic or density
inhomogeneities, on the magnetohydrodynamic (mhd) waves of an
infinite plasma is investigated. The appropriate dispersion formulae,
in both Cartesian and cylindrical polar coordinate geometries, are
derived. The main properties of the allowable modes in structured
plasmas are described, particularly those featuring in a slender
inhomogeneity.
The inclusion of non-adiabatic effects is examined, specifically
for a thermally dissipative, unstratified, finite structure and for
a slender inhomogeneity in a stratified medium. The dissipative time
scales of slender structures are shown to have a dependence on the
Peclet number. Growth factors appropriate to these time scales for
the overstable motions of a thermally dissipative, Boussinesq fluid
are derived.
For the linear analysis of a slender structure it is shown
that the dispersive nature of the waves is deducible from the
simplified one-dimensional equations. The analysis is extended,
for slender structures, to nonlinear motions and the governing
equation representing an effective balance between nonlinear,
dispersive and dissipative effects, the Benjamin-Ono-Burgers
equation, is established. The solutions of this equation are
considered and, for weakly-dissipative systems, are shown to be
slowly decaying solitons.
The importance, in the context of group velocity, of the
dispersive nature of waves in ducted structures is discussed and
analogies are made with other ducted waves, for example, the Love
waves of seismology. It is suggested that the behaviour of such
waves, following an impulse, may account for the range of
oscillatory behaviour, the quasi-periodic and short time scales,
observed in both the solar corona and Earth's magnetosphere.
Density variations across a structure and the structure's
curvature, with possible applications to coronal loops, are also
considered.
Further suggestions for possibly identifying some of the
theoretical results with observed behaviour in sunspots, chromospheric
fibrils and spicules are also made.
en
University of St Andrews
The University of St Andrews
QA927.E3
Wave-motion, Theory of
Nonlinear waves
Waves
Magnetohydrodynamic waves in structured atmospheres
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/25692020-07-16T13:33:07Zcom_10023_126com_10023_31col_10023_129
Samuel, Ifor D. W.
Turnbull, Graham A.
Yang, Ying
221
2012-04-24T13:40:34Z
2012-04-24T13:40:34Z
2010-06
uk.bl.ethos.552482
http://hdl.handle.net/10023/2569
This thesis describes a number of studies on organic semiconductors as laser gain media with the aim of simplifying the excitation scheme and exploring potential applications.
A hybrid device taking the advantage of high power inorganic light emitting diodes (LEDs) and low threshold organic distributed feedback lasers is demonstrated to realize a LED pumped organic laser. When the drive current is higher than 152 A, a sharp peak is clearly observed in the laser output spectrum, implying the LED successfully pumps the polymer laser above threshold. This is the first time an incoherent LED has been used as the excitation source for an organic semiconductor laser. A strategy for further improving the performance of the hybrid device is explored with the use of a luminescent concentrator made of a dye doped SU8 film, to intensify the power density from the inorganic LED. The luminescent concentrator is capable of increasing the incident power density by a factor of 9 and reducing the lasing threshold density by 4.5 times.
As a preliminary investigation towards mode-locked polymer lasers, the impact of a solid state saturable absorber on a solution based organic semiconductor laser is explored. The dye doped polystyrene thin film saturable absorber exhibits a saturation intensity of a few MW/cm². When it is placed into the laser cavity, a train of short pulses is generated and the underlying mechanism is discussed.
Finally, the potential of using organic semiconductor lasers in the detection of nitro-aromatic explosive vapours is studied in distributed feedback polyfluorene lasers. A high sensing efficiency and fast response from the laser prove polyfluorene lasers can be used as disposal and low cost devices in explosive chemosensing.
en
University of St Andrews
The University of St Andrews
Organic electronics
Lasers
Hybrid optoelectronics
Distributed feedback
TA1700.Y2
Semiconductor lasers
Organic semiconductors
Light emitting diodes
Organic semiconductor lasers : compact hybrid light sources and development of applications
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/3752019-07-01T10:17:20Zcom_10023_126com_10023_31col_10023_129
Turnbull, Graham A.
Vasdekis, Andreas E.
Engineering and Physical Sciences Research Council (EPSRC)
174
2007-09-14T15:27:42Z
2007-09-14T15:27:42Z
2007-07-16
http://hdl.handle.net/10023/375
This thesis describes a number of studies of microstructured optical resonators,
designed with the aim of enhancing the performance of organic semiconductor lasers
and exploring potential applications. The methodology involves the micro-engineering
of the photonic environment in order to modify the pathways of the emitted light and
control the feedback mechanism. The research focuses on designing new organic
microstructures using established semi-analytical and numerical methods, developing fabrication techniques using electron-beam lithography, and optically characterising the resulting structures.
Control of the feedback mechanism in conjugated polymer lasers is first investigated by studying Distributed Feedback or photonic crystal resonators based on a square feedback lattice. This study identified the diffraction to free space radiation as a major source of loss in current microstructured resonator designs. By cancelling the coupling to free space through the use of different feedback symmetries and diffraction orders, a threshold reduction by almost an order of magnitude is demonstrated.
The introduction of mid-gap defect photonic states in an otherwise uniformly periodic
structure was studied in Distributed Bragg Reflector (DBR) resonators. This enabled
GaN diode pumped polymer lasers to be demonstrated, indicating that the transition
from complex excitation sources to more compact systems is possible. Devices for
potential applications in the field of optical communications are also explored by
demonstrating a polymer DBR laser based on silicon. In this way, the potential for
integrating conjugated polymers with silicon photonics is confirmed.
Photonic crystal fibres, which have a periodic microstructure in the transverse
direction, are explored as an alternative means for controlling the optical properties of organic lasers. Fluidic fibre organic lasers were demonstrated as efficient sources with good spectral purity. In these devices, mechanisms to tune the emission wavelength
were explored and the origin of the frequency selection mechanism was investigated.
The author received a Wingate Scholarship for the Si experiments.
4199208 bytes
application/pdf
en
University of St Andrews
The University of St Andrews
Creative Commons Attribution-NoDerivs 3.0 Unported
http://creativecommons.org/licenses/by-nd/3.0/
Microstructures
Organic semiconductors
Photonic crystals
Fibres
Fluidics
Diffraction
TA1677.V2
Lasers--Resonators
Semiconductor lasers
Microstructure
Organic semiconductors
Fluidic devices
Photonic crystals
Microresonators for organic semiconductor and fluidic lasers
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/146692019-04-01T10:03:21Zcom_10023_126com_10023_31col_10023_129
Allen, J. F.
Lerski, Richard A.
97 p.
2018-06-27T14:39:51Z
2018-06-27T14:39:51Z
1974
http://hdl.handle.net/10023/14669
The high resolution magneto-optic method using the Faraday effect in thin films of EuS:EuF₂has been used to observe the dynamic intermediate state induced by the passage of an electric current or a heat current through thin slabs of the superconductors Pb, In and Sn. The ease with which the various intermediate state topologies could be made to move has been studied and several features of the interaction of moving flux with pinning sites have been noted. In the case of the current induced motion the measured characteristics of flux flow velocity versus current have been found to exhibit two distinct regions. Firstly, a linear region where the observed velocity was found to agree reasonably well with the predictions of the recent general theory of Andreev and Dzhikaev when allowance was made for the effects of pinning by the introduction of a velocity independent pinning force. Secondly, a curved region was found for currents close to the critical current J₀ in agreement with earlier work using other methods of observation. Possible reasons for the existence of this curvature were examined in detail, and. it was found, that a phenomenological model based, on the presence of a Gaussian distribution of critical current values throughout the sample could account satisfactorily for the observations. The presence of such a Gaussian distribution was confirmed by observing the variations in distance travelled by a domain subjected, to a pulsed, driving current. The curvature was found in disagreement with the theory of thermal activation and. no evidence could be found, for the presence of a velocity dependent pinning force. In the case of the thermally induced, motion which was investigated only in Pb, it was found, in agreement with the very recent work of Laeng and Rinderer, that there exist two competing mechanisms driving the flux. The first of these, that treated, by Andreev and Dzhikaev in their general theory, which acts in a direction parallel to the heat flow, was found to be effective at low temperatures (T ≪ 4.2K) but to be negligible at high temperatures. The magnitude of the velocity produced by this mechanism agreed reasonably well with the theory at low temperatures but was in complete disagreement at high temperatures when the theory predicts that it should still be observable. The second mechanism which acts perpendicularly to the heat flow dominated the motion at high temperatures but its magnitude did not agree with the predictions of the recent theory of Rothen, which ascribes the effect to the thermoelectric power of the normal state. It should be noted that to overcome the pinning all of the low temperature observations (T ≪ 4.2k) were performed in the presence of an electric current. Clearly, much more work requires to be done to clarify these observations.
en
University of St Andrews
The University of St Andrews
QC612.S8L3
Superconductivity
Some properties of the dynamic intermediate state in type 1 superconductors
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/144142019-04-01T10:03:22Zcom_10023_126com_10023_31col_10023_129
Hollingsworth, Helen M.
161 p.
2018-06-21T14:37:10Z
2018-06-21T14:37:10Z
1966
http://hdl.handle.net/10023/14414
en
University of St Andrews
The University of St Andrews
QB875.H7
Stars--Spectra
The calculation of stellar opacity
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/143152019-04-01T10:03:24Zcom_10023_126com_10023_31col_10023_129
Dunn, Malcolm H.
Ferguson, Allister Ian
214 p.
2018-06-20T10:32:32Z
2018-06-20T10:32:32Z
1977-09
http://hdl.handle.net/10023/14315
This thesis describes the design and development of a frequency doubled, continuous wave dye laser and its application to a study of the high Rydberg states of Rubidium. The laser uses the dye rhodamine 6G as the active medium and is optically pumped with an argon ion laser. Frequency doubling is by an ADA (ammonium dihydrogen arsenate) or ADP (ammonium dihydrogen phosphate) crystal located within the laser cavity. Continuous output powers in the ultra-violet in excess of 30 mW and tunable over the wavelength range 285-315 nm have been produced. The linewidth can be chosen to be 0.02 nm broadband system) or 0.002 nm (narrowband system) depending on the frequency selecting elements used. In order to keep insertion losses small the crystals have optical faces cut at Brewster's angle, and in order to increase generation efficiency the intracavity radiation field is focused into the crystal. Such an arrangement introduces the aberrations of coma and astigmatism which must be compensated by suitable cavity design. A variety of cavity and crystal configurations have been analysed for aberrations, and a novel arrangement for the simultaneous elimination of coma and astigmatism developed. Several practical frequency doubled dye lasers have been investigated. In particular the performances of ADA and ADP as the frequency doubling crystals are compared and contrasted. ADA has the advantage that it can be non-critically phase matched at these wavelengths and this results in a higher generation efficiency and a better UV beam quality than encountered with ADP. However, since it can only be temperature tuned, the tuning range (292-302 nm for temperature range 20-80°C) is more limited than that for ADP (285-315 nm) which can also be angled tuned. For both types of crystal, thermal phase mismatching is identified as the process limiting generation efficiency. Evidence is also presented that thermal focusing ultimately limits the UV output power by upsetting cavity stability. A computer model of intracavity frequency doubling has been developed. Thermal phase mismatching effects in the crystal as well as excited state absorption in the dye are included. This model is used to investigate the influence of cavity losses and crystal absorption on generation efficiency. Optimization of conversion efficiency by correct choice of crystal parameters is considered. Two systems have been developed to allow continuous scanning over an extended frequency range. One allows the broadband laser (0.02 nm) to be continuously tuned over 3 nm, the other allows the narrowband laser (0.002 nm) to be continuously tuned over 2 nm. The operation of a single frequency version of the laser and its stabilization on an external reference cavity is also described. The excitation of high Rydberg states in Rubidium using the frequency doubled laser is described. The states are detected by a space-charge limited ionization detector. The principal series of Rb up to a principal quantum number of n = 74 has been detected. A novel triode arrangement of electrodes in the space charge detector has enabled a small electric field to be applied to the rubidium vapour. The consequent Stark mixing of n2S, n2P and n2S states has allowed the n2S and n2D states to be excited from the 52S ground state. New term values of the n2S and n2D series are reported.
en
University of St Andrews
The University of St Andrews
TK7872.L3F3
Lasers
Dye lasers
Frequency doubled continuous wave dye lasers
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/146952019-04-01T10:03:25Zcom_10023_126com_10023_31col_10023_129
Andrew, E. Raymond (Edward Raymond)
Eades, Robert G.
106 p.
2018-06-28T10:07:15Z
2018-06-28T10:07:15Z
1952
http://hdl.handle.net/10023/14695
The phenomenon of nuclear magnetic resonance is closely related to the molecular beam experiments and to microwave spectroscopy. Its significant feature is that the magnetic resonance principle, first applied to the molecular beam technique, has been extended to solids, liquids and gases in their normal physical states. In addition to providing yet another important method of measuring nuclear magnetic properties, this newer technique gives a means of investigating the establishment of the thermal equilibrium which is essential to the methods of obtaining very low temperatures; further, the resonance absorption spectrum yields information of crystal structures, phase transitions in solids and information about hindered rotation of molecules in solids. Thus the phenomenon can be used to study certain problems of the solid state. This thesis gives an account of such an application.
en
University of St Andrews
The University of St Andrews
QC765.E2
Magnetic materials
Nuclear magnetic resonance in some solid hydrocarbons
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/146592019-04-01T10:03:26Zcom_10023_126com_10023_31col_10023_129
Tunstall, D. P. (David Prestwich)
Webster, Wendy J.
Science and Engineering Research Council (SERC)
University of St Andrews
315 p.
2018-06-27T13:01:59Z
2018-06-27T13:01:59Z
1994
http://hdl.handle.net/10023/14659
Static nuclear magnetic resonance (NMR) techniques have been used to study the magnetic hyperfine interactions of ⁶³Cu and ⁸⁹Y nuclei in the superconducting (T=1.5K) and normal (T=160-300K) states of the pure and cobalt doped Y-Ba-Cu-O layered cuprate systems. Sample quality and physical characteristics are well supported by magnetic susceptibility. Hall effect and X-ray diffraction measurements. We report ⁶³Cu NMR spin echo experiments, performed at 1.5K and 141MHz, on a uniaxially aligned sample of undoped YBa₂Cu₃O₇. By working at such low temperatures T, we provide clear confirmation that the spin components of the ⁶³Cu Knight shift, at both crystallographic sites and in all directions, vanish as T→0, leaving the orbital shift as the residual shift. This is indicative of singlet spin pairing in the superconducting state. The size and anisotropy of the ⁶³Cu(1,2) orbital shifts are consistent with a localised moment model in which there is a single hole of dₓ₂-[sub]y₂ (d[sub]y₂-[sub]z₂) symmetry in the d-shell shell of the Cu(2) (Cu(1)) ion. By working at high fields, where the demagnetisation corrections are much smaller, we are able to conclude that the disparity in the Kᶜorb(1,2) results from previous studies can be traced directly to discrepancies in the demagnetisation corrections, while inconsistencies in the Kᵃ, ᵇorb(1,2) components result from difficulties in analysing the restricted powder pattern.
The effects of the atomic substitution of Co into the YBa₂(Cu₁-ₓMₓ)₃O₆.₉ (0≤x≤0.04) system have been investigated via an integrated ⁸⁹Y and ⁶³Cu NMR study on aligned powders. Combined susceptibility, X-ray and NMR measurements indicate that the Co ion substitutes preferentially at the Cu(1) site and bears a magnetic moment of around 3.7μB, consistent with a Co³⁺ localised moment of intermediate spin state (s=1). Theoretical modelling of the dipolar fields induced by such a moment suggest that the ⁸⁹Y and ⁶³Cu(2) NMR shifts and linewidths cannot be explained by a dipolar mechanism alone. The T[sub]c of the system is found to plateau at ~92K for x%<2.8, but then falls rapidly. This change in T[sub]c is found to coincide with a macroscopic orthorhombic (O) to tetragonal (T) structural transition at x=2.8%. The presence of a true O→T transition is also supported by changes in the ⁸⁹Y chemical shift. Falling hole concentration with increasing x indicates that T[sub]c is not determined by the planes hole concentration alone. Correlations between the ⁸⁹Y Knight shift and T[sub]c, and between ⁸⁹Y magnetic shifts for Co doped and oxygen depleted samples with the same T[sub]c, suggest that decreases in T[sub]c result from a reduction of the DOS at the Fermi level and that the mechanism responsible for T-dependent behaviour in both systems may be the same and directly related to T[sub]c. The complete devastation observed in the low temperature c//B ⁶³Cu(2) spectra for x%>0.5 is consistent with strong inhomogeneity in the Van Vleck component of the planes susceptibility. Finally, correlations between the ⁸⁹Y and ⁶³Cu(2) Knight shifts provide strong evidence in favour of a single quantum spin fluid.
en
University of St Andrews
The University of St Andrews
QC611.6W3
A study of the high temperature superconductor YBa₂Cu₃O₇-𝛿 and its cobalt-doped derivative
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/66012019-04-01T10:03:28Zcom_10023_126com_10023_31col_10023_129
Bonnell, Ian Alexander
Lucas, William
268
2015-04-30T12:17:01Z
2015-04-30T12:17:01Z
2015-06-24
http://hdl.handle.net/10023/6601
The centre of the Milky Way, commonly referred to as the Galactic Centre, is roughly that region within 500 pc of the central black hole, Sagittarius A*. Within the innermost parsec around the supermassive black hole Sagittarius A* are more than a hundred massive young stars whose orbits align to form one or possibly two discs. At about 100 pc is a ring containing more than ten million solar masses of molecular gas which could be the origin of some of the most massive star clusters in the Galaxy. I have performed a number of numerical simulations to help us understand how it is that these structures may have been formed.
I firstly describe and test an improvement to the smoothed particle hydrodynamics code I used. This improves conservation of energy and momentum in certain situations such as in strong shocks from supernovae, which were to be included in a later chapter.
The discs of massive stars around Sagittarius A* are believed to have been born there within fragmenting gaseous discs. This is problematic, as the formation of two stellar discs would require two gaseous counterparts. A method is described of forming multiple discs around a black hole from a single cloud’s infall and subsequent tidal destruction. This is due to its prolate shape providing a naturally large distribution in the direction of the angular momentum vectors within the cloud. The resulting discs may then go on to form stars.
Energetically, it would appear that a sequence of supernovae could potentially cause a giant molecular cloud to fall inwards towards the central black hole from an originally large orbit around the Galactic Centre. I simulate the impact on a giant molecular cloud of supernovae originating from a massive stellar cluster located a parsec away. Ultimately, the supernovae are found to have little effect.
Finally, I simulate the formation of the dense ring of clouds observed in the Central Molec- ular Zone at a distance of about 100 pc from Sgr A*. Infalling gas is shown to be subject to such extreme tidal forces that a single cloud of gas is extended to form a long stream. The ribbon grows to the point that it self-intersects and forms a ring-like structure. Its complexity depends on the orbit of the original cloud. The position-velocity data is compared with observations, and similarities are noted.
en
University of St Andrews
The University of St Andrews
Lucas, WE, Bonnell, IA, Davies, MB, & Rice, WKM, 2013, MNRAS, 433, 353 (doi:10.1093/mnras/stt727)
Astronomy
Astrophysics
SPH
Galactic Centre
Star formation
Milky Way
The Galaxy
QB806.L8
Stars--Formation--Mathematical models
Galactic center
Hydrodynamics
Gas flow and star formation in the centre of the Milky Way : investigations with smoothed particle hydrodynamics
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/36822019-07-01T10:16:47Zcom_10023_126com_10023_31col_10023_129
Dholakia, Kishan
Rudhall, Andrew Peter
166
2013-06-13T09:21:53Z
2013-06-13T09:21:53Z
2013-06-26
http://hdl.handle.net/10023/3682
Broadband spectral content is required to support ultrashort pulses. However this
broadband content is subject to dispersion and hence the pulse duration of corresponding ultrashort pulses may be stretched accordingly. I used a commercially-available adaptive ultrashort pulse shaper featuring multiphoton intrapulse interference phase scan technology to characterise and compensate for the dispersion of the optical system in situ and conducted experimental and theoretical studies in various inter-linked topics relating to the light-matter interaction.
Firstly, I examined the role of broadband ultrashort pulses in novel light-matter interacting systems involving optically co-trapped particle systems in which inter-particle light scattering occurs between optically-bound particles. Secondly, I delivered dispersion-compensated broadband ultrashort pulses in a dispersive microscope system to investigate the role of pulse duration in a biological light-matter interaction involving laser-induced cell membrane permeabilisation through linear and nonlinear optical absorption. Finally, I examined some of the propagation characteristics of broadband ultrashort pulse propagation using a computer-controlled spatial light modulator. The propagation characteristics of ultrashort pulses is of paramount importance for defining the light-matter interaction in systems. The ability to control ultrashort pulse propagation by using adaptive dispersion compensation enables chirp-free ultrashort pulses to be used in experiments requiring the shortest possible pulses for a specified spectral bandwidth. Ultrashort pulsed beams may be configured to provide high peak intensities over long propagation lengths, for example, using novel beam shapes such as Bessel-type beams, which has applications in biological light-matter interactions including phototransfection based on laser-induced cell membrane permeabilisation. The need for precise positioning of the beam focus on the cell membrane becomes less strenuous by virtue of the spatial properties of the Bessel beam. Dispersion compensation can be used to control the temporal properties of ultrashort pulses thus permitting, for example, a high peak intensity to be maintained along the length of a Bessel beam, thereby reducing the pulse energy required to permeabilise the cell membrane and potentially reduce damage therein.
en
University of St Andrews
The University of St Andrews
Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported
http://creativecommons.org/licenses/by-nc-nd/3.0/
Pulse shaping
Multiphoton
Nonlinear optics
Second harmonic generation
Photoporation
Phototransfection
Optical tweezing
Optical binding
Bessel beam
Beam shaping
Ultrashort pulses
Biophotonics
Biophysics
Novel beam shapes
Dispersion
Chromatic dispersion
Temporal dispersion
Spatial dispersion
Spatial distortion
Spatio-temporal pulse shaping
Nonlinear absorption
Multiphoton absorption
Permeabilisation
Dispersion compensation
Spatial light modulator
Frequency domain
Time domain
Spatial domain
Broadband ultrashort pulses
Prism
Beam characterisation
Light-matter interaction
Linear absorption
Multiphoton intrapulse interference
Multiphoton intrapulse interference phase scan
MIIPS
Pulse duration
Time-bandwidth product
Cell membrane
Chirp
Chirp compensation
Adaptive pulse shaper
QC689.5L37R8
Laser pulses, Ultrashort
Dispersion--Experiments
Ultrashort laser pulse shaping for novel light fields and experimental biophysics
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/87862019-04-01T10:03:29Zcom_10023_126com_10023_31col_10023_129
Wan, Kong K.
Hodkin, Malcolm
152
2016-05-12T10:34:12Z
2016-05-12T10:34:12Z
1990
uk.bl.ethos.253551
http://hdl.handle.net/10023/8786
The rampant success of quantum theory is the result of applications of the 'new' quantum
mechanics of Schrödinger and Heisenberg (1926-7), the Feynman-Schwinger-Tomonaga Quantum
Electrodynamics (1946-51), the electro-weak theory of Salaam, Weinberg, and Glashow (1967-9),
and Quantum Chromodynamics (1973-); in fact, this success of `the' quantum theory has depended
on a continuous stream of brilliant and quite disparate mathematical formulations. In this carefully
concealed ferment there lie plenty of unresolved difficulties, simply because in churning out fabulously
accurate calculational tools there has been no sensible explanation of all that is going on. It is even
argued that such an understanding is nothing to do with physics. A long-standing and famous
illustration of this is the paradoxical thought-experiment of Einstein, Podolsky and Rosen (1935).
Fundamental to all quantum theories, and also their paradoxes, is the location of sub-microscopic
objects; or, rather, that the specification of such a location is fraught with mathematical inconsistency.
This project encompasses a detailed, critical survey of the tangled history of Position
within quantum theories. The first step is to show that, contrary to appearances, canonical quantum
mechanics has only a vague notion of locality. After analysing a number of previous attempts at a
`relativistic quantum mechanics', two lines of thought are considered in detail. The first is the work
of Wan and students, which is shown to be no real improvement on the usual `nonrelativistic' theory.
The second is based on an idea of Dirac's - using backwards-in-time light-cones as the hypersurface
in space-time. There remain considerable difficulties in the way of producing a consistent scheme here.
To keep things nicely stirred up, the author then proposes his own approach - an adaptation
of Feynman's QED propagators.
This new approach is distinguished from Feynman's since the propagator or Green's function
is not obtained by Feynman's rule. The type of equation solved is also different: instead of an
initial-value problem, a solution that obeys a time-symmetric causality criterion is found for an
inhomogeneous partial differential equation with homogeneous boundary conditions.
To make the consideration of locality more precise, some results of Fourier transform theory are
presented in a form that is directly applicable.
Somewhat away from the main thrust of the thesis, there is also an attempt to explain the
manner in which quantum effects disappear as the number of particles increases in such things as
experimental realisations of the EPR and de Broglie thought experiments.
en
University of St Andrews
The University of St Andrews
QC174.17L7H7
The pursuit of locality in quantum mechanics
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/142912019-04-01T10:03:30Zcom_10023_126com_10023_31col_10023_129
Slebarski, T. B.
Vincent, Fiona
Robert Cormack Bequest Fund
293 p.
2018-06-20T08:20:23Z
2018-06-20T08:20:23Z
1979
http://hdl.handle.net/10023/14291
Six minor planets with mean motions approximately commensurable with that of Jupiter were observed photographically: (87) Sylvia, (107) Camilla, (414) Liriope, (909) Ulla and (1574) Meyer (all with ratio 9/5), and (334) Chicago (ratio 3/2). The plates were measured on a two-coordinate measuring-machine, and reduced by the method of plate constants. Orbits were derived for all except (1574) Meyer; for (334) Chicago and for (909) Ulla, two orbits were obtained for successive years, though in the former case the orbits were not accurate. The orbits of all six planets were also integrated numerically by computer, together with that of (153) Hilda, using a technique applied to the latter planet by J. Schubart. Based on the three-body problem, this applies three mutually-perpendicular components of the disturbing force to the orbital parameters, which consequently vary with time. Short-period variables are eliminated by averaging; only the longitudes of the two planets are allowed to vary, around one cycle of the commensurability. The derivatives of the orbital elements are calculated at intervals around the cycle, and their average values used in the integration. Schubart's original method neglects the orbital inclinations of both planets; this investigation extends the equations to include the inclinations. His results for (153) Hilda are reproduced, and shown not to change greatly whether the inclinations are included or omitted. For (909) Ulla, however, considerable differences are found. The results of the integrations on all seven orbits are presented in the form of graphs, covering time-intervals of 3000 years and more. The orbit of (909) Ulla was integrated twice, once taking the ratio of mean motions as 9/5, and again as 7/4. The integrations of (153) Hilda and (334) Chicago took the ratio as 3/2. All the orbits considered appear stable over long time-intervals. The perihelion advance of (334) Chicago is interrupted by long retrogressions, as noted by Schubart. The orbit of (909) Ulla shows similar, though less marked, behaviour. Both planets are somewhat removed from exact commensurability. Comparison was made between the orbits of four of the planets, derived from observations, and the orbits predicted by the numerical integrations. In most cases, the orbital parameters changed in the direction predicted but .to a greater degree, indicating that more variables affect the real orbits of the minor planets than are taken into account in this theoretical investigation.
en
University of St Andrews
The University of St Andrews
Aberdeen University Computer Centre; St Andrews University Computing Laboratory; St Andrews University Observatory
QB603.M6V5
Planets--Congresses
The long-period effects of perturbation by Jupiter on the orbits of minor planets with commensurable mean motions
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/220272022-04-14T08:03:56Zcom_10023_126com_10023_31col_10023_129
Padgett, Miles
Steers, Darren
174p
2021-04-08T09:04:22Z
2021-04-08T09:04:22Z
1999
http://hdl.handle.net/10023/22027
This thesis reports the development of novel static Fourier transform spectrometers based upon Wallaston prisms and compact detector arrays. The path difference between orthogonal polarisation states of the input light varies smoothly across the aperture of the prism forming an interferogram in the spatial, rather than temporal, domain that is recorded with the detector array. A Fourier trans¬ form of this interferogram gives the spectral distribution of the incident light. The elimination of moving parts from the design makes the recorded interferogram inherently stable.
I have developed an improved spectrometer utilising Wallaston prisms fabricated from materials of opposite sign birefringence. This new instrument has a significantly increased field of view compared with previous Wollaston prism based spectrometers.
Additionally my work has involved the construction and evaluation of spectrometers for operation in the ultraviolet, visible and infrared regions of the spectrum. These spectrometers have been applied to the analysis of gasolines. Important properties such as gasoline brand and octane number have been identified from ultraviolet and near-infrared spectra using principal component analysis. Finally, I adapted the spectrometer design to make a fibre-coupled laser wavelength meter based on a modified Wollaston prism. For a narrow linewidth source a fringe period measurement technique, used as an alternative to the Fourier transform algorithm, obtains precision measurement (1 part in 10^6) of the centre wavelength. The wavelength meter and spectrometers have numerous applications in the held of general laboratory instrumentation and their robust, compact nature makes them particularly suitable where held based operation is required.
en
University of St Andrews
The University of St Andrews
QC373.S7S8
Fourier transform spectroscopy
Static Fourier transform spectrometers and laser wavelength meters
Thesis
Doctoral
PhD Doctor of Philosopy
oai:research-repository.st-andrews.ac.uk:10023/46542019-07-01T10:04:05Zcom_10023_126com_10023_31col_10023_129
Priest, E. R. (Eric Ronald)
Steele, C. D. C.
Science and Engineering Research Council (SERC)
161 p.
2014-04-29T10:26:52Z
2014-04-29T10:26:52Z
1990
uk.bl.ethos.278125
http://hdl.handle.net/10023/4654
In this thesis magnetostatic and thermal equilibria of
several coronal magnetic structures are considered.
A model is set up for the eruption of a prominence
(modelled as a twisted flux tube) magnetically coupled to a
coronal mass ejection (an overlying void and magnetic
bubble). Two different prominence models are considered. In
one a globally stable equilibrium becomes unstable and, in
the other, equilibrium ceases to exist. In both cases, the
components accelerate upwards before reaching constant
velocities in a manner consistent with observations.
A cylindrically symmetric magnetic arcade in equilibrium
with its axis on the photosphere is subjected to a base
pressure perturbation. The perturbation is examined with the
aim of seeking equilibrium configurations close to the
original equilibrium. It is found that equilibria can only be
found when the integral of the excess base pressure is zero.
For an initial arcade whose field increases linearly with
radial distance from the axis, neighbouring equilibria have
been found.
Equations of thermal equilibrium along coronal loops
with footpoint temperatures of 2 x 10⁴K are solved. Three
fundamentally different categories of solution are found,
namely hot loops, (corresponding to the hot corona), cool
loops (relevant to fibrils, cool cores, and active-region
prominences) and hot-cool loops with cool summits but much
hotter parts between the summit and the footpoints.
Quiescent prominences may be modelled as hot-cool loops
inclined to the prominence axis. Furthermore, warm loops at
intermediate summit temperatures (8 x 10⁴K to 4 x 10⁵ K)
can exist, but the observed differential emission measure
suggests these are uncommon. Thermal catastrophe may occur
when the loop length or pressure is too small.
Many loops can be superimposed to form a coronal
arcade. Two types of arcade are considered - one has its
axis on the photosphere; the other is isobaric and has its
axis below the photosphere. In both cases, cool material can
exist high in the corona as is observed for prominences.
en
University of St Andrews
The University of St Andrews
Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International
http://creativecommons.org/licenses/by-nc-nd/4.0/
QA927.S8
Equilibrium and eruption of solar coronal magnetic structures
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/138952019-04-01T10:03:32Zcom_10023_126com_10023_31col_10023_129
Little, Christopher E.
Little, Laura
230 p.
2018-06-11T11:27:20Z
2018-06-11T11:27:20Z
1998-06
http://hdl.handle.net/10023/13895
This thesis reports the first comprehensive comparison of the operating regimes of the three major types of Cu halide laser, which oscillate on the 510.6 nm and 578.2 nm resonance-metastable transitions of atomic Cu in pulsed discharges at 10-50 kHz pulse recurrence frequency. The three lasers had similar active volumes (36.8-43.5 cm3) and bores (12.5-13 mm), were excited using the same power supply and circuit and monitored using the same diagnostic apparatus. The CuBr-Ne laser produced an annular output beam, weighted towards the yellow transition, with a maximum average output power of 3.55 W and a maximum efficiency of 0.71 %. When H2 gas was added to this laser at a level of ~5%, the output beam developed an axial (central) peak in intensity, the beam was less constricted, the balance of green and yellow powers was improved, the output power rose to a maximum of 11.4 W and the maximum efficiency reached 1.47 %. In both of these lasers, the CuBr vapour was generated by heating a sidearm of the discharge tube. The vapour was entrained in a flow of Ne buffer gas to seed the active volume. A Cu hybrid laser, where CuBr is generated in the tube in situ by reaction of the discharge products of a Ne-HBr buffer gas with Cu pieces in the tube, has been compared to the two conventional CuBr lasers. The Cu hybrid laser also produced an output beam with a central maximum, little or no constriction and a good balance of green and yellow powers. Maximum average output power reached 12.8 W and the maximum efficiency was 1.66%. In terms of specific average output power, the hybrid laser was clearly superior to the other two, with values of 82 mW.cm-3 (CuBr), 262 mW.cm-3 (CuBr-H2) and 348 mW.cm-3 (Cu hybrid). The specific output power of the Cu hybrid laser obtained in these studies is a record value for any Cu laser (including elemental Cu lasers) of tube bore ~12.5 mm. This result and the general dependences of output power on buffer gas pressure, additive (H2, HBr) pressure, pulse recurrence frequency and charging voltage and capacitances are discussed in detail in terms of the fundamental processes and chemical reactions. The most important processes responsible for the high powers and efficiencies and the Gaussian-like beam profiles in the presence of hydrogen are dissociative attachment of HBr in the interpulse period and at the beginning of the pulse, and the reduction of CuxBrx polymers and monomers by H2 to free Cu atoms in the active volume. This is the first time that the importance of hydrogen reduction in these lasers has been identified. Without it, the filling in of the annular output beam cannot be explained. The mechanism of Cu seeding of the hybrid laser has also been studied in detail, as it is the most obvious difference between the Cu hybrid and conventional CuBr lasers. The basic reactions of the seeding process are described, and it is found that in addition to Cu3Br3 and Cu4Br4 polymers there must be a substantial amount of CuH in the discharge to account for the large density of Cu atoms in free form and locked up in molecular forms. This is the first time that CuH has been suggested as a major Cu-bearing species. The process of Cu dendrite formation in the tube is also discussed. Finally, the properties of the hybrid laser have been considered from the point of view of scaling to very high average output powers. It has been shown that average output powers of 1 kW are possible using current technology.
en
University of St Andrews
The University of St Andrews
TK7871.35L6
Gas lasers
Comparative studies of copper bromide lasers
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/110082019-04-01T10:03:33Zcom_10023_126com_10023_31col_10023_129
Hilditch, R. W.
McFarlane, Thomas M.
Science and Engineering Research Council (SERC)
351p.
2017-06-16T11:55:04Z
2017-06-16T11:55:04Z
1986
uk.bl.ethos.571494
http://hdl.handle.net/10023/11008
Spectroscopic and photometric observations of six late-type contact and near-contact binaries are presented, and the results of the analyses discussed. Absolute dimensions have been deduced for three systems: YY Ceti. CX Aquarii and RV Corvi.
YY Ceti, which has an orbital period of 0.79 days, is found to be composed of a normal main-sequence star of spectral type A8 and an evolved G-type star which completely fills its Roche lobe. We argue that the system will evolve into contact within approximately 10 9 years, either by the nuclear evolution of the primary component, or by the loss of angular momentum via magnetic braking. We also propose that this may represent a route to the A-type contact binaries which does not involve a passage through the W-type phase.
The binary CX Aquarii, which has an orbital period of 0.56 days is found to have a similar configuration to YY Ceti, except that its primary component is a main-sequence star of spectral type F5 with an evolved companion of spectral type G9. We argue that the system should achieve contact by loss of angular momentum via magnetic braking within approximately 108 years if the
atmosphere of the primary component is convective, or within approximately 5 x 108 years if the primary possesses a radiative atmosphere.
RV Corvi is found to consist of an unevolved F2 primary component with a K-type companion which has a much larger radius and luminosity than expected for its mass. The system has an orbital period of 0.75 days. Although the binary may be semi-detached, with the primary component completely filling its Roche lobe, it is most probably in a state of marginal contact. In order to obtain a solution to the photometric data it was necessary to treat the secondary component albedo as a free parameter, yielding a value greater than unity. This result implies that there is an abnormal distribution of luminosity on the surface of the binary, which may be interpreted either as an excess of light on the facing hemisphere of one or both of the components, or as a deficit of light on the averted hemisphere of the secondary.
The three remaining binaries, EZ Hydrae, AD Phoenicis and RS Columbae, were all identified as contact systems: EZ Hydrae as a W-type system of orbital period 0.45 days, AD Phoenicis as an A-type system of period 0.38 days, and RS Columbae as an A-type system with a period of 0 .67 days. Although a value for the mass ratio of EZ Hydrae had been obtained from spectroscopic observations, no photometric solution could found because of severe 'disturbances' in its light curve. From our sample of six systems, AD llioenicis and RS Columbae were the only two for which there were no spectroscopic observations. Although photometric solutions were obtained for both systems, these were very insensitive to the value of mass ratio,
which tended toward the physically unrealistic value of unity.
The results for YY Ceti, CX Aquarii and RV Corvi are combined with the published masses, radii and luminosities of 21 other contact and near-contact binaries. It is shown that the primary
components of all contact and near-contact systems are normal main-sequence stars with radii and luminosities appropriate to their masses. The secondary components of the B-type systems and the W-type systems are all overluminous for their masses, due mostly to the radii being increased by a factor of ~1.7. However, these secondary components are segregated on the H-R diagram, where the W-type secondaries appear to the left of the main sequence band due to luminosity transfer from the primary components. The secondary components of the A-type contact systems all have radii and luminosities substantially larger than expected for their masses.
en
University of St Andrews
The University of St Andrews
QB835.M5
Variable stars
An investigation of contact and non-contact binary systems
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/219982022-03-21T10:24:56Zcom_10023_126com_10023_31col_10023_129
Bijl, D
Taylor, Claude Brechin
83 p
2021-04-08T09:04:12Z
2021-04-08T09:04:12Z
1961
http://hdl.handle.net/10023/21998
en
University of St Andrews
The University of St Andrews
QC373.S7T2
Electron paramagnetic resonance spectroscopy
Low temperatures
A paramagnetic resonance spectrometer for the investigation of free radical species in solids at low temperatures
Thesis
Doctoral
MSc Master of Science
oai:research-repository.st-andrews.ac.uk:10023/143182019-04-01T10:03:34Zcom_10023_126com_10023_31col_10023_129
Cairns, Alan
Johnson, David A.
SERC
215 p.
2018-06-20T10:32:45Z
2018-06-20T10:32:45Z
1995-07
http://hdl.handle.net/10023/14318
Recent advances in the development of high power short pulse laser systems has opened a new regime of laser plasma interactions for study. The thesis is presented in two parts. In Part I, we consider the implications of these high power laser pulses for the interaction with a uniform underdense plasma, with particular regard to plasma-based accelerators. We present a scheme for the resonant excitation of large electrostatic Wakefields in these plasmas using a train of ultra-intense laser pulses. We also present an analysis of the resonant mechanism of this excitation based on consideration of phase space trajectories. In Part II, we consider the transition from linear Resonance Absorption to nonlinear absorption processes in a linear electron density profile as the intensity of the incident radiation increases and the scale length of the density profile decreases. We find that the electron motion excited by an electrostatic field exhibits some extremely complicated dynamics with bifurcations to period doubling and chaotic motion as the strength of the driving field is increased or the density scale length is decreased. We also present some results obtained from particle simulations of these interactions.
en
University of St Andrews
The University of St Andrews
TK7872.L3J7
Lasers
High power lasers
Some aspects of nonlinear laser plasma interactions
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/143902019-04-01T10:03:35Zcom_10023_126com_10023_31col_10023_129
Hill, Philip W.
Brown, Alexander
Science Research Council (Great Britain)
University of St Andrews
182 p.
2018-06-21T10:44:36Z
2018-06-21T10:44:36Z
1978
http://hdl.handle.net/10023/14390
Faint blue stars situated out of the galactic plane have been studied using a variety of techniques. Stromgren photometry has been obtained for a number of these stars and classifications derived from the photometry. An interference filter centred at 3775 A near the Balmer discontinuity has been used in conjunction with the Stromgren filters. Observation of Stromgren standard stars, bright B stars and faint blue stars have been used to study the behaviour of the colours (u-38) and (38-b). Reddening-free parameters [u-38] and [38-b] have been evaluated and [38-b] is found to be linearly related to the Crawford H𝛽 index for B-type dwarfs, giants and supergiants. This relationship has been used to derive absolute magnitudes and distances for faint apparently normal B stars. [38-b] allows this work to be done at fainter magnitudes than possible with H𝛽 photometry. A filter pair centred on the HeII 𝜆4686 line has been used to study 0-type stars including 0 subdwarfs. The resulting index is strongly correlated with the equivalent width of the Hell line and has a range of 0ᵐ.13. It is possible to separate sd0, 0 and 0f stars using this index. Although the index is correlated with absolute magnitude for 0 and 0f stars, the detailed behaviour precludes the accurate determination of absolute magnitude for dwarfs and giants. Theoretical indices have been computed from the models of Kudritzki and agree well with the results for stars with high helium abundance. These computations suggest that it is possible to separate sdO and DO stars with this system. The results have also been compared with the work of Auer and Mihalas. 30 A/mm image tube spectra have been used for Ealmer line width measurement and radial velocity determination. The line widths were used to estimate surface gravities for faint blue stars in conjunction with temperatures determined from the Stromgren [u-b] index. The results indicate that 30 A/mm image tube spectra can be used successfully for surface gravity determination. 75 A/mm image tube spectra have been used for spectral classification as a check on the classification provided by Stromgren photometry. The kinematics of certain subdwarfs and main sequence stars at high galactic latitude have been considered. Proper motions have been employed as a check for subluminosity using appropriate absolute magnitudes. Galactic orbits have been computed using the Schmidt model of the galactic force field. Several B-type dwarfs and subdwarfs were found to have been ejected from the galactic plane at high velocity. Thirty percent of the stars previously classified as normal dwarfs were found to be subluminous. The evolutionary implications of these results are discussed.
en
University of St Andrews
The University of St Andrews
QB843.B8
Early stars -- Congresses
An investigation of certain problems related to the classification and physical properties of faint blue stars
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/1432019-07-01T10:08:36Zcom_10023_126com_10023_31col_10023_129
Krauss, Thomas F.
Ayre, Melanie
x, 184 leaves
2006-11-21T18:54:15Z
2006-11-21T18:54:15Z
2006-06
http://hdl.handle.net/10023/143
Photonic Crystal structures have been heralded as a disruptive technology
for the miniaturization of opto-electronic devices, offering as they do the
possibility of guiding and manipulating light in sub-micron scale waveguides.
Applications of photonic crystal guiding - the ability to send light around sharp
bends or compactly split signals into two or more channels have attracted a
great deal of attention. Other effects of this waveguiding mechanism have
become apparent, and attracted much interest - the novel dispersion surfaces
of photonic crystal structures allow the possibility of “slow light” in a dielectric
medium, which as well as the possibility of compact optical delay lines may
allow enhanced light-matter interaction, and hence miniaturisation of active
optical devices. I also consider a third, more traditional type of photonic
crystal, in the form of a grating for surface coupling.
In this thesis, I address many of the aspects of passive photonic crystals,
from the underlying theory through applied device modelling, fabrication
concerns and experimental results and analysis. Further, for the devices
studied, I consider both the relative merits of the photonic crystal approach
and of my work compared to that of others in the field. Thus, the complete
spectrum of photonic crystal devices is covered.
With regard to specific results, the highlights of the work contained in this
thesis are as follows:
Realisation of surface grating couplers in a novel material system
demonstrating some of the highest reported fibre coupling efficiencies.
Development of a short “injecting” taper for coupling into photonic
crystal devices.
Optimisation and experimental validation of photonic crystal routing
elements (Y-splitter and bend).
Exploration of interfaces and coupling for “slow light” photonic crystals.
5586866 bytes
application/pdf
en
University of St Andrews
The University of St Andrews
Creative Commons Attribution-NonCommercial-NoDerivs 2.5 Generic
http://creativecommons.org/licenses/by-nc-nd/2.5/
Photonic crystal structures
Light
TK8304.A8
Crystal optics
Photonics
Optoelectronic devices
Optical wave guides
Photonic crystal interfaces: a design-driven approach
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/111062019-04-01T10:03:36Zcom_10023_126com_10023_31col_10023_129
Lesurf, J. C. G.
Smith, Graham Murray
342 p.
2017-06-28T13:09:03Z
2017-06-28T13:09:03Z
1990
uk.bl.ethos.320530
http://hdl.handle.net/10023/11106
A study of high frequency millimetre wave oscillators is performed operating at W- band and above, using test bench equipment designed and constructed in St. Andrews. Octave tuneable oscillators have been designed, constructed, and used to characterise developmental Gunn devices, as well as to provide ideal oscillators for test bench measurement systems. These oscillators have been sold to many millimetre-wave laboratories throughout Britain. The operation, optimisation and characterisation of these oscillators is described in detail, and various non-linear effects are explained and modelled successfully. The wideband tuneability and matching has also allowed evaluation of new developmental Gunn devices to accurately determine the optimum operating frequency range of the devices. This was part of a developmental program by GEC Hirst and MEDL which has now produced state of the art GaAs Gunn oscillators at 94GHz.
Much of the characterisation of the oscillators is performed using novel quasi-optical techniques, which has allowed low loss accurate performance at these very high frequencies. Several quasi-optical techniques are described and the design, manufacture and evaluation of many optical components are given. In particular, the frequency and harmonic content of the oscillators was determined using a Martin-Puplett Interferometer which utilised a frequency counting technique. This enabled easy wideband measurements to be performed with much greater accuracy than traditional cavity wavemeters. In addition, a state of the art noise bench has been designed and constructed for operation at W -band and above, that utilises a novel open resonator to effect a very high Q suppression filter. The system has been shown to make noise measurements at much lower power levels and with greater sensitivity than comparable systems.
en
University of St Andrews
The University of St Andrews
TK7872.O7S6
Oscillators, Electric
Transferred electron oscillators at MM wave frequencies and their characterisation using quasi-optical techniques
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/74512019-04-01T10:03:38Zcom_10023_126com_10023_31col_10023_129
Di Falco, Andrea
Reader-Harris, Peter
xiii, 118 p.
2015-09-11T15:43:53Z
2015-09-11T15:43:53Z
2016-06-22
uk.bl.ethos.667516
http://hdl.handle.net/10023/7451
Nanoplasmonics has provided a way to control light with extremely high precision, into nanoscale volumes. In many circumstances, the nanoplasmonic devices which can be realised are fabricated using processing techniques which rely on planar technologies.
This thesis provides a general method to make nanoplasmonic devices on a flexible membrane structure, which can be free standing, extremely thin (less than the wavelength of visible light), but retains the ability to be manipulated without loss of optical function. These devices are very pliant and conformable. Flexibility allows the integration of nanoplasmonic devices into many new applications where curved surfaces or the ability to conform to another object is required, as well as providing a route for post-fabrication tunability. Two specific applications are considered: lab-on-fibre technology and surface enhanced Raman spectroscopy.
Lab-on-fibre technologies have been advancing the ability to miniaturise experiments which would normally require a whole laboratory. Fabricating a membrane and then later applying it to the fibre decouples the choice of fibre from the design of the device. Surface enhanced Raman spectroscopy is a powerful diagnostic tool which can uniquely identify an optical fingerprint of different molecules. The technique has been held back from widespread clinical adoption because of the difficulty of reproducibility of the substrates used. A repeatable and reliable rigid substrate is demonstrated, which can identify the concentration of a three component mixture of physiologically relevant biomolecules. This same design is then shown in a flexible form factor, which is applied to a non-planar landscape where it can identify the locations where a molecule of interest has been deposited.
This thesis details the development of the fabrication protocol, the construction of experimental apparatus for characterisation, and the use of numerical modelling to advance the flexible nanoplasmonic membrane platform.
en
University of St Andrews
The University of St Andrews
Nanoplasmonics
Flexible materials
Optics
Filtering
Lab-on-fibre
TA1530.R4
Plasmons (Physics)
Nanophotonics
Nanotechnology
Membranes (Technology)
Flexible membranes for nanoplasmonic applications
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/281252023-08-15T02:01:26Zcom_10023_126com_10023_31col_10023_129
Lovett, Janet Eleanor
Fisher, Stuart Ronan
Engineering and Physical Sciences Research Council (EPSRC)
Carnegie Trust for the Universities of Scotland
Weizmann UK. Making Connections Grant
302
2023-08-09T09:46:20Z
2023-08-09T09:46:20Z
2023-11-29
http://hdl.handle.net/10023/28125
https://doi.org/10.17630/sta/570
1996168
Double electron electron resonance spectroscopy is a versatile and powerful tool for probing paramagnetic systems such metalloproteins and proteins with conjugated spin labels. Chapter 1 introduces EPR theory and the molecular biological concepts that this work is based on. This lays the groundwork with regard to basic knowledge and principles that the following chapters rely on. Chapter 2 collates the methodology used in all aspects of the work conducted in this body of work so that the techniques used may be critically assessed and the work reproduced under the same conditions in future experimentation. Chapter 3 focuses on the in-silico investigation of human calmodulin1 and applies a combinatorial approach utilising bioinformatic and computational techniques towards site selection for site-directed spin labelling and the elucidation of calmodulin1 conformational states through production of simulated models and predictions for expected DEER distance distributions. This ranges from literature reviews, structural region identification and degree of conservation assessment through to AI generated predicted models for secondary and tertiary structures and spin label modelling across different predicted conformational states and predicted distances. Chapter 4 provides a detailed explanation of the experimental work conducted to produce the variants of interest and the subsequent in-vitro process of data acquisition with details on a case-by-case basis. This focuses on the interactions between calmodulin1, Ca²⁺ and the M13 peptide. Chapter 5 takes a look at a comparative labelling technique that takes advantage of a rigid diHis motif for Cu²⁺ spin labelling in combination with MTSL (R1 when peptide-conjugated) for Cu²⁺NTA-R1 measurements that have been previously conducted in chapter 4 and utilises a different technique for distance measurements, RIDME. This chapter also applies other applications of RIDME to different spin systems, this time measuring distances between HisTag-bound Mn²⁺ and R1, taking advantage of another type of spin labelling technique.
"This work was supported by the UK Research and Innovation (UKRI) Engineering and Physical Sciences Council (EPSRC) EP/N509759/1 Project Ref: 1996168, Carnegie Trust Research Incentive Grant and UK-Weizmann Bluston Making Connections Award."--Funding
en
DEER and RIDME Datasets for Calmodulin1 Variants (thesis dataset) Fisher, S. R., University of St Andrews, 4 Aug 2024.
DOI: https://doi.org/10.17630/90d0e0d0-e972-4a03-996a-3ef9e075db1a
https://doi.org/10.17630/90d0e0d0-e972-4a03-996a-3ef9e075db1a
Creative Commons Attribution-ShareAlike 4.0 International
http://creativecommons.org/licenses/by-sa/4.0/
2024-08-04
Thesis restricted in accordance with University regulations. Restricted until 4th August 2024
Double electron electron resonance spectroscopy
DEER
Relaxation induced dipolar modulation enhancement
RIDME
Calmodulin
Electron paramagnetic resonance
EPR
Determination of conformational changes in the structure of human calmodulin-1 using electron paramagnetic resonance spectroscopy
Thesis
Doctoral
PhD Doctor of Philosophy
The University of St Andrews
oai:research-repository.st-andrews.ac.uk:10023/292642024-02-22T03:01:46Zcom_10023_126com_10023_31col_10023_129
Koenig, Friedrich Ernst Wilhelm
Singh, Vyome
Engineering and Physical Sciences Research Council (EPSRC)
111
2024-02-15T15:11:59Z
2024-02-15T15:11:59Z
2021-06-28
https://hdl.handle.net/10023/29264
https://doi.org/10.17630/sta/768
EP/M508214/1
In this thesis I numerically study an optical pulse travelling in a dielectric medium as an analogue event horizon. A novel numerical method is developed to study the scattering properties of this optical system. Numerical solutions of scattering problems often exhibit instabilities. The staircase approximation, in addition, can cause slow convergence. We present a differential equation for the scattering matrix which solves both of these problems. The new algorithm inherits the numerical stability of the S matrix algorithm and converges faster for a smoothly varying potential than the S matrix algorithm with the staircase approximation. We apply our equation to solve a 1D stationary scattering of plane waves from a non-periodic smoothly varying pulse/scatterer travelling with a constant velocity in a lossless medium. The properties of stability and the convergence of the Riccati matrix equation are demonstrated. Furthermore, we include a relative velocity between the scatterer and the wave medium to generalise the algorithm further where the number of right and left going modes are not equal. The algorithm is applicable for stationary scattering process from arbitrarily shaped smooth scatterers, periodic or non-periodic, even when the scatterer is varying at the scale of wavelengths. This method is used to present numerical results for a sub-femtoseconds optical pulse travelling in bulk silica. We calculate the analogue hawking radiation from the analogue system. The temperature of the hawking radiation is studied systematically with many different profiles of pulses. We find out steepness, intensity and duration of the pulse are most important in producing analogue hawking radiation in these systems. A better numerical and theoretical understanding will make the experiments better suited to detect hawking radiation.
en
University of St Andrews
The University of St Andrews
Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International
http://creativecommons.org/licenses/by-nc-nd/4.0/
Black holes
Scattering matrix
S-matrix
Analogue
Event horizon
Numerical methods
Quantum optics
Photonics
Light scattering
Discretization
QC585.7O6S5
Dielectrics--Optical properties
S-matrix theory
Analogue event horizons in dielectric medium
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/145302019-04-01T10:03:39Zcom_10023_126com_10023_31col_10023_129
Derrick, G. H.
Anderson, David Lessells Thomson
Carnegie Trust for the Universities of Scotland
190 p.
2018-06-25T11:08:29Z
2018-06-25T11:08:29Z
1969
http://hdl.handle.net/10023/14530
The object of this thesis is to examine the stability of particle-like solutions of the nonlinear field equation
▽²Ψ - 1/c² δ²Ψ/δt² = K²Ψ –μ² ΨΨ*Ψ+λ(ΨΨ*)²Ψ
with the particular form of time-dependence
Ψ = φ (r) e ⁻ ˡʷᵗ
Initially our interest is concentrated on the case λ = 0. We begin the analysis by finding spherically symmetric particle-like solutions, and then examining the stability of the lowest-order solution by first- order perturbation theory. Direct perturbation methods are then considered. This solution is found to be highly unstable whether it is time-independent (ω = 0) or not (ω ≠ 0).
The more general case λ ≠ 0 is next discussed. Particle-like solutions are found to exist in this case for
-∞ < λ (K² - w²/c²) μ⁴ < 3/16
On examining the stability of the lowest-order solutions of this generalised field equation, it is found that for correct choice of the field parameters stable time-dependent solutions can exist, some of which can also have the attractive feature that their energy density is positive definite. We conclude by considering some methods of extending the theory.
en
University of St Andrews
The University of St Andrews
Department of Theoretical Physics
QC173.A6
Atoms
The stability of particle-like solutions of some non-linear field equations
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/145262019-04-01T10:03:40Zcom_10023_126com_10023_31col_10023_129
Osborne, D. V.
Martin, Colin N. B.
Science Research Council (Great Britain)
150 p.
2018-06-25T10:33:17Z
2018-06-25T10:33:17Z
1969
http://hdl.handle.net/10023/14526
Measurements of drag forces an spheres end a cylinder in open rectangular channels in liquid helium II heat flow and superflow wore mode at temperatures between 1.3°K and the λ-point. The drag forces were measured by the deflection of a torsion system suspended above the free surface of the liquid from a quarts fibre. In the heat flow experiments, the drag vas found to be similar to that which would be exerted by a classical fluid with the same velocity, viscosity and density as the norma1 component. Correlations of the drag coefficient D/( ½ ρ[sub]n²A) with the Reynolds numbers ρnᵛηᵈ/ηn and ρᵛnᵈ/ηn show that the former is much more suitable both in tor of eliminating temperature dependence and agreement with the classical value. Above 1.6°K, a small decrease in drag with increasing velocity was usually noticed; this was attributed to the onset of turbulence in the superfluid, giving rise to a component of drag in the direction of superfluid flow. Describing the turbulent superfluid so a laminarly flowing fluid with an effective viscosity ηs makes possible an ardor of magnitude estimate of ηs the decrease in drag; it is found to lie between 10 and 100 micropoise. At temperatures nearer the λ -point, the simple two fluid description appears to become lies adequate. In the superflow experiments, sphere an the cylinder arc dragged in the direction of the superfluid flow. Correlations of drag coefficient with Reynolds number suggest value for the effective viscosity of between 20 and 100 micropoise. In the cylinder superflow experiments, below a velocity of 2±1 am sec⁻¹, no drag was observable. This is attributed to an ideal flow regime and is bellowed to be the first direct demonstration of D'Alembert's wades, rely that an inviscid fluid can exert no drag on a body.
en
University of St Andrews
The University of St Andrews
QC151.M2
Fluid dynamics
Drag forces in liquid helium II
Thesis
Doctoral
PhD Doctor of Philosophy
oai:research-repository.st-andrews.ac.uk:10023/137652019-04-01T10:03:41Zcom_10023_126com_10023_31col_10023_129
Dunn, Malcolm H.
Poustie, Alistair J.
Carnegie Trust for the Universities of Scotland
191 p.
2018-06-06T10:49:07Z
2018-06-06T10:49:07Z
1990-07
http://hdl.handle.net/10023/13765
A study of magnetic field induced sum frequency mixing (SFM) in sodium vapour was carried out using continuous-wave lasers as the sources of the fundamental radiation. The three-wave mixing nonlinear optical process was resonantly enhanced by tuning the laser frequencies close to single and two-photon resonances in the sodium atoms. The coherent ultraviolet radiation at the sum frequency of the two input laser frequencies was emitted by the coherently driven 3S-4D electric-quadrupole, which was rotated by the transverse magnetic field to allow collinear generation of the sum frequency wave. Two single-frequency dye lasers were used to examine in detail the role of the intermediate 3P atomic states in the coherent two-photon absorption. Resonant single photon transitions were investigated for the first time in a nonlinear optical process in an atomic vapour. High resolution SFM line profiles were obtained which illustrated the complicating contributions of hole-burning, velocity selection, optical pumping, saturation and frequency dependent phase mismatching to the three-wave mixing effect. The use of additional single photon resonant enhancement and control over the refractive index of the sodium vapour showed that large effective nonlinear X(2) susceptibilities were possible in atomic vapours which could exceed those of nonlinear crystals. The variation of SFM power with atomic particle density due to bulk phase mismatching reflected the wavelength dependence of the sodium dispersion with the 3P intermediate state off-resonance. Phase shifts of the focused Gaussian laser beams led to an asymmetric behaviour of the phase matching with respect to the sign of the phase mismatch k. Saturation spectroscopy was utilised for the first time to examine the Zeeman spectra of the sodium 3S-3P D line resonances in a transverse magnetic field. A novel experimental method was used to restrict the detrimental effects of velocity changing collisions on the resolution of the nonlinear laser spectroscopic technique. The possibility of using optical pumping with a transversal, resonant light beam to induce the second-order nonlinearity necessary for second harmonic generation in sodium vapour was experimentally investigated.
en
University of St Andrews
The University of St Andrews
TK7871.3P7
Lasers
Magnetic field induced sum frequency mixing in sodium vapour
Thesis
Doctoral
PhD Doctor of Philosophy
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