Spatial scales of coherence of diffraction-free beams in a turbulent atmosphere

Abstract

Coherent properties of diffraction-free optical beams propagating in a turbulent atmosphere are studied. The analysis is based on the solution of the equation for the second-order mutual coherence function of an optical radiation field. The behavior of the degree of coherence of the diffraction-free (cosine and fundamental Bessel) optical beams depending on the beam parameters and characteristics of the turbulent atmosphere is investigated. It turns out that the oscillating character of the degree of coherence of these beams is a fundamental property of diffraction-free beams, which is shown under weak fluctuations in a turbulent atmosphere. At high levels of fluctuations in a turbulent atmosphere, the degree of coherence of a diffraction-free cosine beam becomes closer to that of a plane wave, and of a diffraction-free fundamental Bessel beam, to a spherical wave. The analysis of two spatial scales of the degree of coherence of optical beams has shown that the integral scale of the degree of coherence for diffraction-free beams is a more representative characteristic than the coherence length; the former definitely correlates with optical radiation propagation conditions in a turbulent atmosphere.