Thermal self-interaction of a multimode optical beam in a turbulent medium

Thermal self-interaction of a Gaussian partially coherent optical beam in a turbulent medium is studied by a numerical analysis of the parabolic equation for the mutual coherence function. An investigation is made of the envelope and radius of spatial coherence both along the propagation path of the beam and in its transverse cross section. It is found that as the input radiation power increases, the increase in the radius of the beam envelope is mainly due to nonlinear refraction and turbulent pulsations of the medium strongly influence the spatial coherence of the beam. Thermal nonlinearity restricts the decrease in the coherence radius in a turbulent medium although the spatial coherence of the beam as a whole deteriorates.