Optical Properties of Microparticle Suspensions

Suspensions of microparticles in a liquid host medium are known to possess very large optical nonlinearity (large chi^3), whilst also exhibiting the unusual phenomenon of enhanced backscattering. We have for the first experimentally studied the relationship between these two effects using wavelength-scale latex spheres in aqueous solutions. The experiment shows the change in the half-power angular width of the enhanced backscattering peak varies as 1/sqrt{ rm I} where I is the intensity of the illuminating radiation. A numerical model based on the diffusion approximation is developed to explain these results. It qualitatively agrees with the experimental results except a higher illuminating intensity is required in the model to induce a similar change of the angular width of the enhanced backscattering peak observed experimentally.