Methods for control of the small-scale structure and depolarization of radiation due to diffraction

An analysis is made of methods for improving the quality of radiation propagating in laser systems using "soft" diaphragms (apertures) and spatial filters. These involve solving the problem of diffraction of a plane electromagnetic wave by a circular diaphragm for arbitrary distances from the diaphragm, taking into account large diffraction angles. By solving the appropriate diffraction problems, the diaphragm parameters can be optimized. It is found that the amplitude distribution of the field can be efficiently controlled by varying the diaphragm radius of a spatial filter. It is suggested that absorbing diaphragms may be used to suppress depolarization of the radiation due to diffraction.