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 are theoretically analyzed. A quasi-optical equation is obtained, which differs from the traditional equation by the complexity of the diffraction coefficient, and this leads to effective diffusion of radiation in anisotropically absorbing media. Because of this, the intensity of minima observed in the far-field region in the case of diffraction of coherent radiation by a slit does not vanish, but has a finite value. The solution for Gaussian beams is constructed. It is shown that the beam width increases as the square root of the path length in an anisotropic medium, whereas the angular divergence varies in inverse proportion to the square root of the path length.