The physical model of strong optical scintillation of plane waves is extended to the case of spherical-wave propagation. The spherical-wave amplitude filter function is derived and compared to the corresponding plane-wave result. Specifically, we calculate the spherical- to plane-wave log-amplitude-variance ratio. For weak fluctuations, our results are identical to the results of perturbation theory, with which the spherical-wave log-amplitude variance is less than the corresponding plane-wave result. On the other hand, for strong fluctuations (i.e., in the saturation regime), the plane- and spherical-wave log-amplitude variances saturate to the same constant value. Expressions are presented, in the saturation regime, for the plane- and spherical-wave log-amplitude covariance function and compared with the corresponding results in the regime of weak fluctuations.
© 1974 Optical Society of America
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