The Optical Properties of Aerosols

Abstract

Abstract : The purpose of this paper is to present some results for the full scattering pattern from binary aggregates of identical spheres deposited on a plane surface. The extension of our theory to the case of aggregated spheres is far from trivial because one has to consider the effect of the mutual interaction of the aggregated spheres: in other words, we had to modify our theory to account for the dependent-scattering effects in the presence of the plane surface. Of course, aggregated spheres form anisotropic objects whose patterns are expected to have a noticeable dependence on their orientation with respect to the incident field. The field scattered by a dispersion of such objects even when de posited on a surface with a given distribution of their orientations may be rather different from the field scattered by a dispersion of the same objects all oriented alike. Nevertheless, by making full use of the transformation properties of the spherical multipole fields under rotation we are able to calculate, through an analytical average, the field scattered, for instance, by an orientationally random dispersion of aggregates on the surface. This has been achieved by giving a suitable definition of the transition matrix of the aggregate in the presence of the surface. The elements of the transition matrix include, of course, all the interactions among the spheres that compose the aggregate. The resulting patterns, that will be discussed below, should give a reliable description of the physical situation that is likely to be meet in actual experiments.