Techniques for optical tweezers and SLM microscopy

[摘要] With the development of pixelated liquid crystal displays, a new paradigm has emergedin the field of optics. Essentially, these displays enable interfacing a computer programwith 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 thiscase, 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 tweezersand SLM microscopy; this thesis concerns both. The aim of the thesis is to explore anddevelop new techniques combining SLMs with microscopy.The first part of this thesis goes into results of the experiments I have carried outin holographic optical tweezers. Hydrodynamic interactions play an important role inmany physical and biological processes. I present experimental evidence for the partialsynchronisation 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 degreeof synchronisation still exists due to the Brownian motion alone. I then describe a newprocedure to protect the optical trap from contamination in sensitive samples. Microrheologyusing optical tweezers requires lengthy position measurements in order to obtainthe linear viscoelastic properties of fluids and this measurement is often compromisedby freely diffusing material entering the trap. I then apply rotational Doppler velocimetryto a particle spinning in an optical tweezers. This is the first time that structuredillumination has been used to determine rotation rate in the micro regime.The second part describes the development of an SLM microscope and a series ofexperiments I carried out with it. The set up of the microscope is described and imagesare characterised in terms of the point spread function. I also demonstrate the multimodalcapabilities by diffracting three different images, each with a unique spatial frequencyfilter, onto a single camera chip. Next, I report the development of some new frequencyfilters, namely holographic stereo microscopy and three variations, including stereo withdefocus which mimics human binocular vision where we have two eyes (views) of theworld, each having its own lens. I used 3D particle tracking to investigate sedimentationin a confined microscope sample. This experiment brought together SLM microscopy andoptical 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 commontheme being that the SLM is placed in the Fourier plane of the sample. Both holographicoptical 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 particletracking and visualisation with SLM microscopy, whilst microrheology will benefit from the new approaches.

[发布机构] University:University of Glasgow;Department:School of Physics and Astronomy

[关键词] Optical Tweezers, Microscopy