Scattering and Absorption of Light by Nonspherical Dielectric Grains

Abstract

A method is described for calculating approximate extinction, absorption, and scattering cross-sections for dielectric grains of arbitrary shape, with dimensions comparable to or smaller than the wavel&ngth of the incident radiation. The grain is modeled by an array of N polarizable elements in vacuum. The elements are located on a simple cubic lattice, and N is of order of magnitude 100. The polarizability of an element is such that an unbounded array would exhibit, according to the Clausius-Mossotti relation, the bulk dielectric constant of the grain material. The complex vector amplitude of each oscillator in the array, which is driven by the field of the incident wave and the fields of all the other oscillators, is determined by an iterative procedure. From the N amplitudes all the cross-sections, including differential cross-sections, are obtained. The method was tested by comparing the cross-sections computed for "spherical" clusters of oscillators with exact Mie theory values for the corresponding dielectric spheres. Computed cross-sections a-c presented for five different grain shapes and three different complex refractive indices. Subject headings: interstellar matter - opacities polarization