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|Title: ||Study of phase-matching geometries in bulk and periodically-poled lithium niobate and their use in intracavity terahertz optical parametric oscillators|
|Authors: ||Thomson, Caroline L.|
|Supervisors: ||Dunn, Malcolm H.|
Optical parametric oscillator
|Issue Date: ||20-Jun-2012|
|Abstract: ||This thesis describes the experimental implementation of novel intersecting cavity terahertz optical parametric oscillators based on bulk and periodically-poled magnesium oxide-doped lithium niobate. Both collinear and non-collinear phase-matching geometries have been demonstrated and injection-seeding has been implemented in devices using periodically-poled
material to reduce threshold and increase the down-conversion efficiency. A comprehensive characterisation of the original intracavity terahertz OPO was
undertaken, which revealed the parameters having the greatest impact on OPO
efficiency (idler mirror reflectivity and cavity length) and led to a better
understanding of the losses in the system. During the characterisation process,
generation of further terahertz radiation at the same frequency as that generated
by the parametric process was observed and identified as being a result of
difference frequency generation (DFG) between the parametrically-generated
idler and terahertz waves. This phenomenon had previously only been observed
when periodically-poled materials were employed in the system. The effect of
this additional DFG process has been analysed in terms of the enhancement of
the terahertz field on the basis of the coupled wave equations and physically
The use of periodically-poled lithium niobate has been a major part of the
research presented in this thesis.
A comprehensive study of the modified phase-matching conditions was carried out and both collinear and novel hybrid non-collinear phase-matching geometries were identified.
Several computer models were developed to assess the performance of any given grating design in these different geometries and the effects of temperature tuning and pump wavelength variation were also investigated using the models.
Experimental studies confirmed the viability of the modelling approach but material limitations (particularly the early onset of crystal damage) limited the outcomes of the experiments. A detailed comparison of the poled and bulk materials was made to highlight the present drawbacks of the poled material. Finally, injection seeding was used to improve the efficiency of the collinear phase-matched PPLN OPOs. When seeding was used the depletion of the pump
pulse was increased to the point of being measurable, reaching an upper level of
10%. Coupling constraints placed on the seed laser limited the amount of depletion attained. The potential for injection seeding to be used in the hybrid non-collinear phase-matching scheme was also identified but not realised during the course of this work. Were this technique successful, the tuning range of the intersecting cavity terahertz OPO could be extended to encompass the sub-1THz region, something that has previously been limited by the available idler cavity angles.|
|Publisher: ||University of St Andrews|
|Appears in Collections:||Physics & Astronomy Theses|
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