Local field intensity in aggregates illuminated by diffuse light: T matrix approach.

We derive an analytic expression for the local field intensity in an aggregate of particles illuminated by diffuse light (T matrix formalism). To be precise, the diffuse light average is obtained by averaging the electromagnetic response from plane waves over all possible incident field direction polarizations. We applied this new averaging formula to analyze variations in the electromagnetic couplings between two isotropic spheres as a function of their separation distance. The numerical calculations were performed with the recursive centered T matrix algorithm (RCTMA), one of the known analytical solutions of the multiple scattering equation of light. Illustrative calculations clearly demonstrate that diffuse averaging has a large smoothing effect on the strong angular and local variations in the field intensities that are omnipresent in orientation fixed calculations. We believe that this formalism can be a valuable tool in the analysis of electromagnetic couplings in dense random heterogeneous media, in which light propagation is dominated by a scalar diffusion behavior.