Multiple light scattering by spherical particle systems and its dependenceon concentration: A T-matrix study

The T-matrix method has been used to calculate scattering cross-sections of two spherical particles close to each other. By comparing our results with those expected for infinite distance, we can determine the maximum distanc e required to produce interparticle lightscattering interactions. As a resu lt, we can determine the degree of dilution needed in a particle suspension to remain within the single-scattering approximation. Cross sections have been calculated for a relative refractive index m = 1.2 and a range of part icle sizes and separations. Since the approach in this paper assumes double scattering as the first mechanism for beginning multiple scattering, our r esults will be compared with those arising from the condition that the opti cal depth is less than unity, tau < 1. It is shown that this condition, wid ely used in transfer theory, is more restrictive than ours except for the s mallest particles, where double scattering becomes the main agent for multi ple scattering. (C) 2001 Academic Press.