Cylindrical vector beams (CVBs) are the class of laser beams which exhibit azimuthal symmetry in their polarisation structure. These beams exhibit a `donut' intensity profile due to an on-axis polarisation vortex. CVBs have received significant recent interest due to their similarities to the modes of an optical fibre and their interesting focusing properties in the limit of high numerical aperture. This thesis contains an investigation into the properties of CVBs and their applications for optical micromanipulation, using a variety of experimental geometries. First I describe methods for the synthesis of CVBs and explain why CVBs are appealing for optical trapping. This is followed by an experimental investigation of focal volume control using the polarisation state of CVBs in an optical tweezers. Experimental results are complemented by numerical calculations of trapping forces obtained from a theoretical model derived from electromagnetic scattering theory in the T-matrix framework. Next I consider the use of CVBs in a dual-beam fibre-optic trap for trapping of low refractive index particles, such as ultrasound contrast agent microbubbles. The optical trapping forces are calculated numerically for a wide range of parameters. Additionally, the photonic stress profile over the surface of the microbubble is presented together with the resulting optically-induced deformation. The next chapter is an investigation of CVBs in an alternative trapping geometry. Experimental results are presented, demonstrating optical trapping and propulsion of microscopic particles using the evanescent field in the region around a tapered optical fibre. I also consider the plasmonic optical forces on metallic nanoparticles in the evanescent field of a tapered fibre. Finally, I present results of experiments probing the optical coherence properties of higher order CVBs to clarify the differences between coherence and correlation properties of stochastic beams which have a non-uniform polarisation direction.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:587741 |
| Date | January 2013 |
| Creators | Skelton, S. E. |
| Publisher | University College London (University of London) |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://discovery.ucl.ac.uk/1386216/ |
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