Optical extinction, refractive index, and multiple scattering for suspensions of interacting colloidal particles

TL;DR

This paper develops a microscopic theory for light scattering and refractive index in suspensions of interacting colloidal particles, highlighting the importance of multiple scattering, radiation reaction, and structural effects.

Contribution

It introduces a comprehensive microscopic framework that accounts for interactions and multiple scattering effects in colloidal suspensions, extending effective medium theories.

Findings

Multiple scattering encodes structural features in the forward scattered field.

Radiation reaction influences light extinction in suspensions.

Anomalous dispersion effects occur in strongly-interacting colloidal systems.

Abstract

We provide a general microscopic theory of the scattering cross-section and of the refractive index for a system of interacting colloidal particles, exact at second order in the molecular polarizabilities. In particular: a) we show that the structural features of the suspension are encoded into the forward scattered field by multiple scattering effects, whose contribution is essential for the so-called "optical theorem" to hold in the presence of interactions; b) we investigate the role of radiation reaction on light extinction; c) we discuss our results in the framework of effective medium theories, presenting a general result for the effective refractive index valid, whatever the structural properties of the suspension, in the limit of particles much larger than the wavelength; d) by discussing strongly-interacting suspensions, we unravel subtle anomalous dispersion effects for the suspension refractive index.