Computation of small-scale velocity turbulence and its effect on optical scintillations and stimulated thermal Rayleigh scattering.

Coherent high-power light beams propagating long distances through turbulent fluids are subject to many kinds of scattering effects; among these are small-scale thermal index instabilities, in which the fluid is heated by the small fraction of light that is absorbed, amplifying the pre-existing index fluctuations and producing small-angle stimulated thermal Rayleigh scattering. Turbulent velocity fluctuations can inhibit the rate of growth of these instabilities by dispersing the thermal perturbations created by the beam. Methods for computing the turbulent diffusion of the heating perturbations, compatible with fast-Fourier-transform beam propagation computations, are presented. Propagation calculations of scintillation coherence times and small-scale velocity turbulence thresholds for stimulated thermal Rayleigh scattering are included.