Dynamic properties of optical tweezers

Stilgoe, Alexander B. E. (2011). Dynamic properties of optical tweezers PhD Thesis, School of Mathematics & Physics, The University of Queensland.

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Author Stilgoe, Alexander B. E.
Thesis Title Dynamic properties of optical tweezers
School, Centre or Institute School of Mathematics & Physics
Institution The University of Queensland
Publication date 2011
Thesis type PhD Thesis
Supervisor Halina Rubinsztein-Dunlop
Timo Nieminen
Norman Heckenberg
Total pages 174
Total colour pages 11
Total black and white pages 163
Language eng
Subjects 020304 Thermodynamics and Statistical Physics
020303 Fluid Physics
020302 Electrostatics and Electrodynamics
Abstract/Summary Optical tweezers is a classical optics tool for manipulating small dielectric objects which can be used non-invasively in biology, chemistry and physics. At the beginning of this thesis I investigate the construction of various models of optical tweezers from rudimentary dipole scattering through to ray tracing and more complete models using the full electromagnetic properties of highly focused light. I perform sensitivity analysis of the apparatus demonstrating the use of Allan variance measurements in apparatus uncertainty traces. I experimentally investigate the dynamic properties of single and multiple beam versions of the apparatus as it applies to the measurements and the characterisation of microparticles and microparticle flows. This includes a detailed analysis of the specific effects present in spherical scatterers and their behaviour under Brownian motion. I also experimentally consider the hydrodynamic correlations of large spheres which can be easily tracked with high speed camera. In addition, an analysis of the potential application of correlated camera and quadrant photodiode detection to precision measurements is made. I investigated methods of detection of particle motion such as interference patterns in coherent light scattering and quadrant photodiode detection measurements of force using the forward scattered trapping light and found that they provide complimentary information about particle dynamics. I provide an interpretation of the quadrant detector measurements and discuss how the limitations of the collection angle of light can cause reductions in measurement sensitivity. I also demonstrate a novel interaction in multiple-beam optical tweezers which in effect can produce traps with variable stiffness independent of the trapping depth at constant power. Multiple beam optical tweezers for a single particle display phase-transition-like phenomena as they are separated, this makes them an analog of classical states in condensed matter physics. I also apply near-complete models of optical tweezers to analyse interactions of non-conservative forces in both the single and multiple trap regime.
Keyword Optical tweezers
Optical traps
Non-conservative forces
Light scattering
Electromagnetic theory
Statistical mechanics
Lorenz-Mie theory

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Created: Mon, 20 Aug 2012, 18:16:07 EST by Alexander Stilgoe on behalf of Scholarly Communication and Digitisation Service