<title>Optical sensing of fractal aggregates of particles using backscattering enhancement</title>

Abstract

To coherently backscattered light from a dense disordered medium generates an intensity peak in the far field due to the constructive interference in the time-reversal pairs of light. The spatial properties of the particle distribution in the suspension affect characteristics of the peak intensity distribution. In our report, the coherently backscattered light from particles aggregated in dense and absorbent colloidal suspensions is experimentally investigated with relation to the fractal dimension of media. The investigation is concerned with a decreasing slope in the intensity distribution. Dense colloidal suspensions of polystyrene latex spheres are used in the experiment and the aggregation of particles is induced by adding the NaCl solution to colloidal suspensions. As a result, the decreasing slope in intensity distribution changes suddenly at an amount of NaCl solution, which implies the fractal clusters form in the dense suspension. The quantitative estimations for the dimensions of media reveal that the dimension estimated from the copolarized intensity depends both on the distribution of clusters and on the spatial structure inside a cluster whereas the cross- polarized intensity depends only on the spatial structure inside a cluster. Furthermore, it is clearly shown that such a decreasing behavior is independent of absorption.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.