Diffraction phenomena in a dichroic medium

Diffraction phenomena accompanying the propagation of narrow directed beams of coherent radiation in a medium with anisotropy of absorption and gain a re theoretically analyzed. A quasi-optical equation is obtained, which diff ers from the traditional equation by the complexity of the diffraction coef ficient, and this leads to effective diffusion of radiation in anisotropica lly absorbing media. Because of this, the intensity of minima observed in t he far-field region in the case of diffraction of coherent radiation by a s lit does not vanish, but has a finite value. The solution for Gaussian beam s is constructed. It is shown that the beam width increases as the square r oot of the path length in an anisotropic medium, whereas the angular diverg ence varies in inverse proportion to the square root of the path length. (C ) 2001 MAIK "Nauka/Interperiodica".