Surface roughness effects on the transmission of Gaussian beams by anisotropic parallel plates

The influence of plate surface roughness in precise ellipsometry experiments is studied. The realistic case of a Gaussian laser beam crossing a uniaxial platelet is considered. The expression for the transmittance is determined using first order perturbation theory. In this frame, it is shown that interference takes place between the specular transmitted beam and the scattered field. This effect is due to the angular distribution of the Gaussian beam and is of first order in the roughness to wavelength ratio. As an application, a numerical simulation of the effects of the roughness of a quartz surface at normal incidence is provided. The interference term is found to be strongly connected to the random nature of the surface roughness.