AUTOCOLLIMATION MODE IN THE CASE OF REFLECTION OF A 3D GAUSSIAN BEAM FROM A TWO-DIMENSIONALLY PERIODIC GRATING OF SHORT-CIRCUITED RECTANGULAR WAVEGUIDES

摘要

The up-to-date spectroscopic instrumentations are generally designed using reflection diffraction gratings operating in the autocollimation mode. Application of the waveguide-type reflection gratings in the autocollimation mode in designing various devices can provide an essential advantage as compared with the gratings of the non-waveguide type. The scattering of the Gaussian wave beams by two-dimensionally periodic gratings in the autocollimation mode has not been investigated in the past. When analyzing the scattering characteristics of the electromagnetic field of a 3D Gaussian wave beam incident upon a two-dimensionally periodic structure it is necessary to determine the angles of propagation of the non-specular beam. To construct the power dependences of the beam and far-field directional pattern, a novel algorithm is required which is different from that used for analyzing the power characteristics of the specular beam. The autocollimation mode is investigated in the case of reflection of a 3D Gaussian wave beam from a two-dimensionally periodic grating of short-circuited rectangular waveguides. Results are presented for the cases of incidence of p- and s-polarized beams of annular cross-section on a grating with a rectangular mesh. The power reflection factors are calculated for the specular and non-specular beams in dependence on the length of the short-circuited waveguides. The far-field pattern of the reflected beams is analyzed as a function of the grating and incident beam parameters. 3D power far-field patterns of the specular and non-specular beams are calculated. A physical explanation of the effects of energy redistribution between the specular and non-specular beams is suggested. The effect of splitting of the reflected beam directivity pattern has been revealed. The power characteristics and far-field patterns have been first determined for the non-specular beam. Analysis of the obtained results makes it possible to determine under which parameters of the incident beam and the reflection grating the incident beam field can be approximated by a plane wave field.