Abstract

The intensity covariance of a point source of waves propagating in a random medium is calculated using the asymptotic theory and a Kolmogorov refractive-index spectrum with an innerscale cutoff. In strong scattering, the variance is only a function of one parameter. The variance and small correlation scale are both larger than predicted for zero-inner scale. The small-scale structure is controlled by irregularities near the receiver while the large-scale structure is controlled by irregularities near the transmitter. The theoretical predictions are compared to experiment. Higher terms in the asymptotic theory are required in order to adequately predict intensity covariance. Full saturation of intensity fluctuations (variance of unity) is unlikely for laser propagation in reasonable atmospheric conditions. A similar analysis can be applied to the case of a Gaussian beam. The variance of intensity from a Gaussian beam is equal to the point source case when the transmitter aperture is smaller than the Fresnel distance and the beam diameter at the receiver plane is larger than the effective scattering region. The plane wave case is approximated when the transmitter aperture is larger than the scattering region and the radius of curvature is larger than the propagation distance. When the laser beam is focused onto the receiver plane, there is a regime where the variance is independent of the incident beam dimensions.

© 1986 Optical Society of America