Abstract

The optical properties of fractal aggregates and effects of multiple scattering are studied using computer-generated clusters whose structures are known. We show that the dominant effect of multiple scattering is reflected in the mean-field index of refraction of the clusters. By contrast, multiple scattering does not mask the q dependence of the scattering, even when the polarizability of each particle is large, and when d_f > 2, so that the cluster is geometrically opaque. In addition, we show that, in spite of the aggregates’ generally low density, the connected structure necessarily imposes significant high-order multipole interactions between each particle and its nearest neighbors. For metal particles, this results both in the appearance of a second red-shifted absorption peak as distinct from the single-particle Mie resonance as well as strong depolarized scattering.

© 1987 Optical Society of America