Scattering matrix calculated in geometric optics approximation for semitransparent particles faceted with various shapes

Abstract

A new computer model of light scattering by semitransparent particles with arbitrary shape is presented. The model allows calculations of scattering angle dependences of all elements of scattering matrix F ik in geometric optics approximation. Scattering properties of faceted spheres with a number of the facets less than 10,000 differ significantly from those of the perfect spherical particles. The scattering angle dependences of all studied parameters, the element F 11 and ratios— F 12/ F 11, F 34/ F 11, F 22/ F 11, F 33/ F 11, F 44/ F 11, of roughly faceted spherical particles diverge very much from those of perfect spheres showing, as a rule, smoother curves. For binary contacting spheres the optical properties of individual spheres dominate total scattering, excluding only the ratio F 22/ F 11, when two contiguous spheres (due to prominent asymmetry of the aggregate they formed) depolarize incident light very noticeably. The ideal cube gives forward and backward scattering brightness spikes as well as a strong negative polarization branch at large scattering angles. When the cubes are deformed, the spikes are reduced and become wider. The negative polarization branch vanishes. A special class of irregular particles generated with an auxiliary random Gaussian field (RGF) is also studied. The RGF particles with a high degree of irregularity do not reveal backscattering at all. As the degree grows the maximum of the polarization curve diminishes, all details on scattering angle dependences are smoothed, and the negative branch of polarization in the forward scatter direction almost disappears. For all classes of particles, the degree of positive polarization grows at small scattering angles, when k increases. This is a manifestation of the Umov effect. There is a qualitative similarity of the scattering angle curves of all investigated elements of scattering matrix for the roughly faceted spheres and ellipsoids, RGF particles, and strongly deformed cubes. It turns out that strongly irregular particles of all the studied classes reveal much more resemblance, than the perfect representatives of the classes.