Phase behavior near total absorption by a metallic grating

A bare metallic grating illuminated by a plane, S-polarized electromagnetic wave can completely absorb one of the diffracted orders. These strong absorptions have been reported to be accompanied by two different types of behavior. Here we calculate, by means of an exact differential method, the phase versus angle-of-incidence curves for cycloidal metallic gratings with different groove-depth-to-period ratios. We show that an algorithm based on the electromagnetic theory of gratings can account for the experimentally observed behavior in the vicinity of a resonant anomaly. We also show that this type of study provides additional information about the position of the zeros of the scattering matrix in the complex plane.