Angular Momentum in Optical Tweezers

Mr Simon Parkin (2008). Angular Momentum in Optical Tweezers , School of Physical Sciences, The University of Queensland.

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Author Mr Simon Parkin
Thesis Title Angular Momentum in Optical Tweezers
School, Centre or Institute School of Physical Sciences
Institution The University of Queensland
Publication date 2008-01
Supervisor Prof. Halina Rubinsztein-Dunlop
Prof. Norman Heckenberg
Dr. Timo Nieminen
Total pages 148
Total colour pages 22
Total black and white pages 126
Subjects 240000 Physical Sciences
Formatted abstract Optical tweezers, three dimensional optical traps formed by single laser
beams, are powerful tools for quantifying forces in micro-biological systems
such as the molecular motors that drive many cellular process. Optical
tweezers work by transferring momentum from the light that forms the optical
trap to the trapped object. Light also carries angular momentum in the
form of spin and orbital angular momentum. However, there has been limited
use of optical angular momentum to apply and, in particular, measure
optical torque on optically trapped particles.
The aim of this thesis is to rectify this situation through the development
of methods to quantify the transfer of optical angular momentum in
optical tweezers. The methods developed are then used to make measurements
of viscosity on themicroscopic scale,which has applications formicrobiological
systems and small volume medical samples.
We begin by introducing optical tweezers and describing models based
on electromagnetic theory that can be used to calculate the fields within optical
traps, and the forces and torques on the trapped particle. Next we describe
experimental methods to apply and measure optical torques. Results
of the measurements of both spin and orbital angular momentum are presented.
Bearing in mind our goal of conducting microviscometry, we characterise
a birefringent microsphere made from a crystalline polymorph of
calcium carbonate called vaterite. The microparticle’s strong effective birefringence
(¢n = 0.06, measured in optical tweezers) allows efficient application
of optical torque to the vaterite particle and its spherical shape makes it
ideal for probing viscosity. In the final chapter we present the characterisation
of our rotating optical tweezers based microviscometer and preliminary
viscosity measurements within a biological cell and within eye fluid.
Additional Notes The individual page numbers for colour printing (numbers according to the document printing i.e. as per the contents page and the page number label at the top of each page) 7, 17, 19, 21, 29, 30, 35, 36, 38, 41, 48, 49, 51, 57, 60, 68, 69, 71, 86, 89, 104, 105

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Created: Thu, 18 Sep 2008, 14:21:07 EST by Mr Simon Parkin on behalf of School of English, Media Studies and Art History