Modified reflectance and geometrical deformations of Gaussian beams reflected at a dielectric interface

Abstract

The geometrical interpretation of Gaussian-beam deformations under reflection at a linear dielectric interface is revised. It is proved that, besides the four known geometrical effects, namely, the lateral, focal, and angular shifts and the beam-waist modification, an independent nonspecular effect termed the complex amplitude modification exists and that all these effects are necessary for a complete description of the deformed beam. The new effect is described as a product of reflectance and propagation nonspecular modifications. The amplitude-based and intensity-based definitions of the modified reflection coefficient are given, and substantial differences between them and the Fresnel reflectance are shown. The significance of the propagation modification in the evaluation of the modified reflectance is also explained. Analytical expressions for all the nonspecular effects and for the interrelations among them are derived, and an accurate numerical procedure for their evaluation is discussed.