Dynamic speckles formed by focused coherent field scattering from rough surfaces with non-Gaussian statistics

The process of the focused Gaussian beams diffraction from the surfaces with both small and large-scale relief inhomogeneities is considered. The analytical expressions describing the probability function of dynamic speckles intensity fluctuations have been derived. The numerical modeling of focused coherent beam scattering with a small number of scatterers has been conducted. As shown, this case corresponds to non-Gaussian scattered radiation statistics. The range of parameters, when the scattered field statistics are close to Gaussian ones, has been determined. The analysis of probability density function of amplitude fluctuations shows that speckle fields formed when the number of scatterers is small are statistically inhomogeneous ones. It was established how the statistical characteristics of a diffracted radiation depend on the correlation length and the standard deviation of random screen phase fluctuations.