Light scattering by structured spheres

Formulation of the scattering problem as an integral permits calculation of the scattered field without any restrictions upon particle shape or internal structure (distribution of dielectric constant). However, the internal field must be known. Here, we approximate the internal field for a structured sphere by that of a homogeneous sphere whose dielectric constant is obtained from the volume weighted average of the polarizability. This approximation should be accurate for sufficiently small variations of the dielectric constant. The resulting algorithm has been tested by comparison with the boundary value solution for concentric spheres. For dielectric constants corresponding to aqueous suspensions of biological particles, the results are quite accurate for dimensionless sizes (circumference over wavelength) no greater than 7. The backscatter is particularly sensitive to small changes in morphology, including less symmetrical dispositions of the internal structure than those modeled by concentric spheres. Although the algorithm is also accurate for more highly refractive particles (corresponding to atmospheric aerosols), in this case the scattering is much less sensitive to changes in internal structure, even in the backward directions.