Light Induced Self Assembled Colloidal Systems

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Light can move transparent objects at the microscopic scale. This occurs as the object may act like a small lens and bend the light and change its momentum. This causes the particle to be held in the brightest part of the light field. However interesting effects can occur if we use two opposing beams to hold a more than one particle: the very action of the light bent by one object influences the light distribution and thus equilibrium position of the other sphere creating a chain of objects held at distances of many microns from one another: optically bound matter. In systems with many microscopic particles other interesting effects may occur. If we illuminate a large group of such objects they naturally form patterns e.g. organise themselves into lines. For objects larger than the illuminating light, this occurs as each object acts like a lens and refocuses the light and pulls neigbouring objects together: This effect is intricately linked to nonlinear physics and this is a relatively new medium within which to observe phenomena such as solitons: waves that act like particles and in fact may move without any spreading. We aim to fully understand these effects and unfiy the understanding of optical binding and these nonlinear effects. We will realise optical binding in 2 and 3 dimensions as well as use a dye to image the light distribution in the system. The studies may lead to new ways to bind together cells, orgnaise colloidal particles over a large area and other objects creating self assembly of trapped objects to order. Such self assembly and understanding the reasons behind it is useful fora bottom up approach to creating larger crystals