Wavefront reversal in stimulated light scattering in a focused spatially inhomogeneous pump beam

A theoretical analysis is made of stimulated light scattering in a pump beam possessing both fine-structure inhomogeneity (and thus, "gray" divergence) and a continuously varying amplitude and phase envelope due to focusing of the beam with a lens into an unbounded medium. An equation is derived to describe the gain of the pump-reproducing field component, and a solution of this equation, excitable by spontaneous radiation noise, is found in the constant pump field approximation. In this case, the scattered wave is localized in a narrow (compared with the pump wave) near-axial zone and, unlike scattering in a waveguide, the reproduction of the pump wave is partial and dependent on the correlation between the "gray" and diffraction-limited divergence. The disagreement between this theoretical conclusion and the complete reproduction observed earlier experimentally indicates the importance of saturation effects in the scattering of focused beams.