Simon Hanna (Bristol University) is visiting on Wed 30 Jan 2013 to give the AMOP Physics seminar. Simon is a theoretician in the Nanophysics and Soft Matter Group at Bristol with wide-ranging interests including liquid crystals and polymer physics. His talk, however, will be about modelling optical forces on specially shaped micoparticles in optical traps.
Title: Optimising forces and torques for optical micromanipulation, Simon Hanna (Bristol University)
Abstract: The motion of a colloidal particle in an optical field depends on a complex interplay between the structure of the field, and the geometry and composition of the particle. There are two complementary approaches to generating a particular force field. The first, involving sculpting of the optical field with e.g. a spatial light modulator, has been extensively developed. A second method, highlighted recently, involves sculpting of the particles themselves, and has received much less attention. However, as modern two-photon polymerisation methods advance, this avenue becomes increasingly attractive for micromanipulation. In this talk I will show how computational methods may be used to optimise particle geometries in such a way as to produce desirable patterns of forces and torques. These designs are then tested using particles fabricated using the two-photon method. In particular, I will demonstrate the design of a constant force optical spring for use as a passive force clamp, a high efficiency optical wing, and a shape-optimised microtool.