Anomalous retroreflection from nanoporous materials as backscattering by 'dark' and 'bright' modes

In this paper the mechanisms of previously experimentally observed anomalous retroreflection in a strongly absorbing nanostructured medium are explained by using 'dark' and 'bright' modes. The observed regularities are analyzed for both s-polarized and p-polarized incident radiation with respect to the contribution from 'dark' and 'bright' modes and the influence of the absorption on the scattering indicatrix. The theoretical consideration provides explanation not only for the retroreflection itself but explains also correlations with absorption and differences for retroreflection efficiency for s- and p-polarized radiation. The possibilities of using 'dark modes' for processing and transmission of energy are discussed. (paper)