Enhanced backscattering of light by aggregation of particles in an absorbing and dense colloidal suspension

Abstract

The angular intensity profile of the enhanced backscattering of light (EBL) is investigated experimentally with regard to the spatial distribution of particles suspended in a disordered, dense and absorbing medium. Particle aggregation is induced by adding NaCl solution to a colloidal suspension of polystyrene latex particles. We show experimentally that a decay slope of the peak intensity profile decreases suddenly at a certain concentration of NaCl due to the formation of fractal clusters. Such behaviour is shown to be independent of absorption. The dimension of the medium defined as a measure of the particle distribution is estimated by applying the EBL decay slope to the empirical formulae obtained in the previous study by Ishii et al (Ishii?K, Iwai?T and Asakura?T 1997 Opt. Rev. 4 643). As a result, we confirm that the EBL is applicable to the in situ monitoring of the aggregation process of particles without dilution of the suspension or degradation of accuracy by changes in absorption.