Experiments using holographic optical tweezers

Sinclair, Gavin (2006) Experiments using holographic optical tweezers. PhD thesis, University of Glasgow.

Abstract

This thesis mainly describes experiments carried out to advance the techniques of manipulating dielectric particles trapped using holographic optical tweezers. Holographic optical tweezers are a relatively recent advancement in optical trapping, using a spatial light modulator to display holograms that are used to shape the trapping laser beam. In my work, most experiments involved dielectric particles trapped using Gaussian beams to form sample to complex patterns. To allow complex patterns of particles to be trapped, the limits of the spatial light modulator were initially defined to allow a workable trapping volume to be specified. The working volume was defined by determining the efficiency of an optical trap in a pre-defined three dimensional coordinated system, using Stokes drag to find the force exerted by the trap. The working volume was found to be 40 μm by 40 μm by 50 μm, centered around the zeroth diffraction order. Initially complex patterns of particle were trapped in structures resembling cubic and diamond unit cells, using precalculated static holograms. In the cubic unit cell example, the structure could be rotated and its size controlled using cursor controls. The diamond unit cells was difficult to trap using a static hologram and this prompted the manipulation of particles initially trapped in simple two dimensional patterns, then manipulated into more complex two and three dimensional patterns.

An important aspect of the above experimental work was feedback to the developers of the two main algorithms used to design the holograms I used. The two different algorithms used to design these holograms were a direct binary search algorithm developed by Dr Zsolt Laczik and a modified Gerchberg-Saxton algorithm developed by Dr Johannes Courtial. The feedback helped to refine the hologram design process and helped the Glasgow group to develop a suite of tools for hologram design.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: Q Science > QC Physics
• Colleges/Schools: College of Science and Engineering > School of Physics and Astronomy
• Supervisor's Name: Padgett, Prof. Miles and Courtial, Dr. Johannes
• Date of Award: 2006
• Depositing User: Ms Anikó Szilágyi
• Unique ID: glathesis:2006-5894
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 09 Jan 2015 14:57
• Last Modified: 09 Jan 2015 14:59
• URI: https://theses.gla.ac.uk/id/eprint/5894