Angular Grating Anomalies: Effects of Finite Beam Size on Wide-angle Diffraction Phenomena

Diffraction gratings are known to exhibit anomalous behavior at certain critical wavelengths or incident angles. These traditional anomalies manifest themselves as abrupt variations in diffracted order efficiency or grating absorption, while their angular position remains unchanged as predicted by the grating equation. Experimental observations have been reported, indicating a diffraction grating anomaly in the angular position of certain diffracted orders that appears to violate the grating equation. Several exotic physical mechanisms have been suggested as possible causes of this intriguing behavior; however, in this paper we show that this angular grating anomaly is the straightforward result of finite beam size on wide-angle diffraction phenomena, as described by simple scalar diffraction theory.