Intensity of a focused beam in a turbulent medium

The effect of the strength of turbulence on the intensity distribution in the focal plane of a focused laser beam is studied. The intensity in the focal region is found to be unaffected by the turbulence provided Cn²< 0.45 k0^-2S^-5/6F^-1, where Cnis the index of the refraction structure constant, k0is the signal wavenumber, S is the initial cross section of the beam, and F is the focal length.