It is shown theoretically that the spatial coherence radius of the field of a single-mode laser beam traveling in a turbulent atmosphere exceeds the coherence radius of plane and spherical waves. It is established that this excess is greatest in the case of strong fluctuations of the beam intensity. A study is made of the influence of a partial coherence of a light source on the coherence radius of the beam field. It is demonstrated that the radius of the spatial coherence of a beam becomes independent of the diffraction size and coherence of the source when the random phase shifts increase sufficiently over a distance equal to the radius of the first Fresnel zone. A solution is obtained of the problem of turbulence-induced spreading of the image of a partly coherent laser source formed in the focal plane of the receiver lens.
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Belen’kii et al. (1977) studied this question.