Nonspecular astigmatic reflection of a 3D gaussian beam on an interface

Abstract : We extend a recently proposed approach of the study of nonspecular effects to 3D finite beams. It is shown that a new nonspecular effect appears in 3D: the two beam waist in the two transverse directions across the beam are different and their longitudinal positions are different. In other words a plane interface is an astigmatic system for a finite beam. The effect is illustrated by studying the nonspecular effects for the zero order diffracted beam by a grating. It is shown that this system produces strong nonspecular effects due to the efficient coupling of leaky waves near the total absorption regime.