Theoretical and Experimental Investigation of a New Type of Blazed Grating*

Abstract

A rigorous electromagnetic theory of the diffraction of light by blazed lamellar gratings has been developed. It is applied to calculate the diffracted power distribution of four gratings (R1 − R4) whose grooves have the following depths and widths (b,l) in units of grating period a: (0.433, 0.750), (0.333, 0.667), (0.250, 0.500), and (0.200, 0.400). All four gratings are theoretically blazed in the minus-first order for 30° incidence and for the wavelength equal to the grating period. The blaze is, however, broad band, and the minus-first-order theoretical power-conversion efficiency (P−1) for the most interesting grating, R3, exceeds 0.8, 0.9, 0.95, and 0.98 in the wavelength bands 0.84 a−1.49 a, 0.85 a−1.47 a, 0.87 a−1.43 a, and 0.98 a−1.31 a, respectively, for linearly polarized light. These surprising performances, which far exceed those obtainable with echelette gratings insofar as the incident light is linearly polarized, have been experimentally verified with the help of a microwave interference spectrometer, and point to the potential usefulness of blazed lamellar-reflection gratings in far-infrared spectroscopy.