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dc.contributor.advisorDholakia, Kishan
dc.contributor.advisorKrauss, Thomas F.
dc.contributor.authorPloschner, Martin
dc.description.abstractOptical manipulation of nanoscale objects is studied with particular emphasis on the role of plasmon resonance for enhancement of optical forces. The thesis provides an introduction to plasmon resonance and its role in confinement of light to a sub-diffraction volume. The strong light confinement and related enhancement of optical forces is then theoretically studied for a special case of nanoantenna supporting plasmon resonances. The calculation of optical forces, based on the Maxwell stress tensor approach, reveals relatively weak optical forces for incident powers that are used in typical realisations of trapping with nanoantenna. The optical forces are so weak that other non-optical effects should be considered to explain the observed trapping. These effects include heating induced convection, thermoporesis and chemical binding. The thesis also studies the optical effects of plasmon resonances for a fundamentally different application - size-based optical sorting of gold nanoparticles. Here, the plasmon resonances are not utilised for sub-diffraction light confinement but rather for their ability to increase the apparent cross-section of the particles for their respective resonant sizes. Exploiting these resonances, we realise sorting in a system of two counter-propagating evanescent waves, each at different wavelength that selectively guide gold nanoparticles of different sizes in opposite directions. The method is experimentally demonstrated for bidirectional sorting of gold nanoparticles of either 150 or 130 nm in diameter from those of 100 nm in diameter within a mixture. We conclude the thesis with a numerical study of the optimal beam-shape for optical sorting applications. The developed theoretical framework, based on the force optical eigenmode method, is able to find an illumination of the back-focal plane of the objective such that the force difference between nanoparticles of various sizes in the sample plane is maximised.en_US
dc.publisherUniversity of St Andrews
dc.rightsCreative Commons Attribution 3.0 Unported
dc.subjectPlasmon resonanceen_US
dc.subjectOptical sortingen_US
dc.subjectGold nanoparticle sortingen_US
dc.subjectNanoparticle trappingen_US
dc.subjectEnhanced optical forcesen_US
dc.subject.lcshSurface plasmon resonanceen_US
dc.subject.lcshLaser manipulation (Nuclear physics)en_US
dc.titleThe role of the plasmon resonance for enhanced optical forcesen_US
dc.type.qualificationnamePhD Doctor of Philosophyen_US
dc.publisher.institutionThe University of St Andrewsen_US
dc.publisher.departmentSchool of Physics and Astronomyen_US

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