The method of small perturbations is used to calculate the degree of coherence of a gaussian beam in a random medium. The refractive-index fluctuations of the medium are assumed to be small and statistically homogeneous and isotropic. Based on the Kolmogorov spectrum, asymptotic and numerical solutions are obtained for a collimated beam and a focused beam propagating in a turbulent atmosphere. For both the collimated beam and the focused beam, the degree of coherence increases as the value of L/ka2 increases, other parameters being fixed; a is the beam radius. Furthermore, the solution for an infinite plane wave forms the lower bound of the degree of coherence for a collimated beam, and the solution for a spherical wave forms the upper bound for both the collimated beam and the focused beam. These results are explained physically.
© 1970 Optical Society of AmericaFull Article | PDF Article
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