Propagation of focused laser radiation in a turbulent medium

A theoretical study is made of the propagation of focused laser radiation in a random, weakly inhomogeneous medium with large-scale fluctuations, of the refractive index. The analysis is based on the solution of the equation for the fourth-order coherence function. It is shown that spectral and correlation characteristics of intensity fluctuations in a medium with a power-law spectrum of the refractive index fluctuations depend strongly on the mean square of the phase shift in a distance equal to the diameter of the transmitting aperture. An analytic expression for the correlation function of the intensity fluctuations is obtained for high values of this diameter, and an analysis is made of the nature of the saturation of the relative fluctuations of the intensity. The results of the calculations are in agreement with the experimental data.