Study and Control of the Dynamics of Mesoscopic Particles in Optical Tweezers

Roy, Basudev (2014) Study and Control of the Dynamics of Mesoscopic Particles in Optical Tweezers. PhD thesis, Indian Institute of Science Education and Research Kolkata.

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Abstract

This thesis deals with the study of dynamics of particles trapped in optical tweezers. It can essentially be divided into four major chapters of work based on the description and understanding of the systems in which the work was carried out and the resulting applications. In the first chapter, the basic concepts of tightly focused laser beams and the principles of optical tweezers are mentioned. We also described the methods to characterize the tweezers. The second chapter deals with new techniques developed to study rotational and translational motion of particles trapped in tweezers. In the third chapter, perform a thorough theoretical analysis of the spin-orbit interaction (SOI) of light in optical tweezers and investigate the effect of having a stratified medium in the tweezers system on the magnitude of the SOI. We study two types of effects: a) that due to the geometrical phase picked up due to tight focusing through stratified media which results in a polarization dependent intensity profile near the trap focal plane, and b) spin Hall shifts that lead to the formation of regions of large spin angular momentum (SAM) density that are again formed near the trap focal plane. In the fourth chapter, we describe a new method of controlled lithography by using optically produced microbubbles. In the fifth chapter, we study the basic dynamics of the thermo-optically generated bubble growth on different substrates and found that it is essentially convection dominated. We also study the size of the bubbles as function of illumination laser the intensity and find profound dependence on the convective flow surrounding the bubble. We use these bubbles to transport micro-objects like polystyrene beads and even gold and silver nanoparticle clusters. We also show non-equilibrium self-assembly driven pattern formation on the surface of these bubbles. Lastly, we show that these could be used as thermo-optical pumps with fluid velocities higher than other optically induced techniques. We show that these flows can be turned of in about 500 µs.

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