Volume current method for modeling light scattering by inhomogeneously perturbed spheres

Abstract

A volume current method (VCM) for calculating the optical scattering by inhomogeneous spheres is presented. The method is applicable to spheres having small refractive-index perturbations. In this method the internal and scattered fields are approximated with a separation-of-variables solution, in which each mode has its own effective-average refractive index. These fields generate an additional volume polarization current in the regions where the refractive index differs from the average refractive index of the sphere. The fields radiated by these polarization currents are then added to the approximate fields radiated by the unperturbed sphere. When they are tested with off-centered layered spheres, the fields calculated with the VCM compare well with those found with separation of variables so long as the changes in the refractive index are small. When the host sphere is near resonance and the perturbation is in a region where the resonant fields are large, the perturbations must be smaller than when the sphere is off resonance.