Mutual coherence function and frequency spectrum of a laser beam propagating through atmospheric turbulence

Using transport methods, we have computed the mutual coherence function of a laser beam propagating in turbulence with a modified Von Karman spectrum for the index-of-refraction fluctuations, including a parametric study of the effect on the mutual coherence function of varying beam size, focal length, and the properties of the turbulence. The results are valid over nearly all propagation distances, unlike calculations employing the method of smooth perturbations. We have also studied the effect of a constant wind on the frequency spectrum of the signal, and have found that, over most practical path lengths, the spectral width is Δω=4.1 Vk06/5(Cn2)3/5z3/5, where V is the wind speed, k0 is the signal wave number, Cn2 is the strength of turbulence, and z is the path length in the turbulence.