Techniques for optical tweezers and SLM microscopy

Lee, Michael Peter (2014) Techniques for optical tweezers and SLM microscopy. PhD thesis, University of Glasgow.

Abstract

With the development of pixelated liquid crystal displays, a new paradigm has emerged
in the field of optics. Essentially, these displays enable interfacing a computer program
with light, and therefore allow a wide range of light beams to be created. In this thesis,
I shall be using liquid crystal displays to create phase diffraction patterns and, in this
case, the displays are more commonly referred to as Spatial Light Modulators (SLMs).
One area where SLMs have shown particular promise is that of optical microscopy. Here,
they have been used in two different applications, namely holographic optical tweezers
and SLM microscopy; this thesis concerns both. The aim of the thesis is to explore and
develop new techniques combining SLMs with microscopy.
The first part of this thesis goes into results of the experiments I have carried out
in holographic optical tweezers. Hydrodynamic interactions play an important role in
many physical and biological processes. I present experimental evidence for the partial
synchronisation of the stochastic oscillations of two spheres in a bistable optical trap.
This experiment showed that, even in the absence of an external driving force, a degree
of synchronisation still exists due to the Brownian motion alone. I then describe a new
procedure to protect the optical trap from contamination in sensitive samples. Microrheology
using optical tweezers requires lengthy position measurements in order to obtain
the linear viscoelastic properties of
fluids and this measurement is often compromised
by freely diffusing material entering the trap. I then apply rotational Doppler velocimetry
to a particle spinning in an optical tweezers. This is the first time that structured
illumination has been used to determine rotation rate in the micro regime.
The second part describes the development of an SLM microscope and a series of
experiments I carried out with it. The set up of the microscope is described and images
are characterised in terms of the point spread function. I also demonstrate the multimodal
capabilities by diffracting three different images, each with a unique spatial frequency
filter, onto a single camera chip. Next, I report the development of some new frequency
filters, namely holographic stereo microscopy and three variations, including stereo with
defocus which mimics human binocular vision where we have two eyes (views) of the
world, each having its own lens. I used 3D particle tracking to investigate sedimentation
in a confined microscope sample. This experiment brought together SLM microscopy and
optical tweezers to create a new technique for particle sizing, or study surface effects.
This thesis describes several new applications of SLMs in microscopy, with the common
theme being that the SLM is placed in the Fourier plane of the sample. Both holographic
optical tweezers and SLM microscopy have been expanded by the techniques I have developed.
In future, this work will serve as foundation for the combination for 3D particle
tracking and visualisation with SLM microscopy, whilst microrheology will benefit from the new approaches.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Optical Tweezers, Microscopy
• Subjects: Q Science > QC Physics
• Colleges/Schools: College of Science and Engineering > School of Physics and Astronomy
• Supervisor's Name: Padgett, Professor Miles
• Date of Award: 2014
• Depositing User: Mr Michael Lee
• Unique ID: glathesis:2014-5552
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 03 Oct 2014 11:09
• Last Modified: 03 Oct 2014 11:31
• URI: https://theses.gla.ac.uk/id/eprint/5552