Abstract

Wood's anomalies in light reflected by gratings refer to unexpectedly strong variations in the intensity of diffracted orders within narrow spectral bands. Two principal varieties of such behavior have been identified: (a) Rayleigh anomalies, which occur when one of the higher diffracted order is changing from propagating to evanescent, and (b) resonant anomalies, which appear if the incident field is phase matched to the harmonic of a leaky wave guided by the grating. These phenomena have been investigated theoretically for incident plane waves, but the behavior of realistically bounded beams in anomalous conditions has been considered only for very restricted situations. We therefore examine Gaussian beams incident on a simple canonic model of reflection gratings and show that the diffracted beams may exhibit strong spatial (lateral, longitudinal, and angular) shifts as well as a change in their effective cross section. Our results thus provide a unified phenomenological explanation of Wood's anomalies and beam modification phenomena in wave scattering by periodic structures.

© 1989 Optical Society of America