On the frequency correlation of optical radiations propagating in a medium with large-scale random inhomogeneities

The parabolic-equation approach of quasi-optics is used to analyze the frequency correlation of optical beams propagating in a medium with large-scale random inhomogeneities. A comparison of the derived expression with results obtained using small-angle geometrical optics shows that the influence of diffraction effects on the behavior of the 'averaged' frequency correlation of collimated Gaussian beams is insignificant. Attention is given to the question of the correctness of the geometrical-optic description of the frequency correlation of optical beams in the absence of random inhomogeneities.