Backscattering enhancement by randomly distributed very large particles

Recently, the backscattering enhancement by densely distributed particles of a size comparable to the wavelength was reported. It has been explained as the constructive interference of two waves traveling in opposite directions. This enhancement was observed only in densely distributed particles, and its existence in sparsely distributed media has not been verified yet. In this paper we present the experimental evidence of backscattering enhancement by sparsely distributed very large particles. Experiments are conducted using 45-microm latex particles which are approximately 100 times the wavelength. Both copolarized and crosspolarized components are measured for different particle concentrations. Unlike for small particles, backscattering enhancement is most noticeable when the particle concentration is low. The angular width of the peak is comparable to the ratio (wavelength)/(particle size) and is independent of the optical distance.