Intensity fluctuations in forward scattering and temporal coherence.

The problem of forward scattering by a nonergodic system of identical particles is considered. The analysis of statistical characteristics of intensity fluctuations arising as a result of finite observation time shows that the mean dispersion of intensity fluctuations can be expressed as a function of the wavelength, diffusion coefficient, scattering angle, and observation time. The relation between the temporal correlation function of the scattered radiation and its second-order intensity moments is established. Quantitative estimates of the effect with the infrared laser beam propagating through fog give results comparable to the dispersion due to refractive index fluctuations in a pure atmosphere (Tatarskii).