Coherence in the single and multiple scattering of light from randomly rough surfaces.

One of the most interesting phenomena associated with the scattering of light from a randomly rough surface is that of enhanced backscattering. This is the presence of a well-defined peak in the retroreflection direction in the angular distribution of an incoherent component of mean scattered intensity of the light scattered from such a surface that is primarily due to the coherent interference of each multiply reflected optical path with its time-reversed partner. It is an example of a broader class of multiple-scattering phenomena that goes under the name of weak localization. Not all manifestations of weak localization in the interaction of light with a randomly rough surface are in backscattering. It was recently shown that the average diffuse intensity from randomly rough surfaces with even symmetry can be enhanced or reduced in the specular direction because of the constructive interference between correlated pairs of scatters. We present a recent theoretical analysis and experimental results that cover four kinds of enhancement: enhanced backscattering, enhanced transmission, enhanced specular, and enhanced refraction for one-dimensional and two-dimensional surfaces. These are manifestations of coherent effects that remain after ensemble averaging.