Transverse enhancement of coherence of the scattered field in wavefront reversal

A theoretical investigation is made of the "mosaic" regime of wavefront reversal in stimulated backscattering of a pump beam with a small-scale spatial inhomogeneities. The scattered field mainly takes the form of the reversed pump field with a continuously varying (mosaic) envelope. For statistically homogeneous pump radiation with an angular divergence $\theta_L$, the solution obtained describes transverse enhancement of the coherence of the envelope up to the radius $r_c$, which depends on the length of the medium in accordance with $r_c\backsim z^{1/2}$ and, under conditions typical of stimulated Brillouin scattering, is given by $r_c\thickapprox z\theta_L$. The mosaic-induced angular scatter of the beam reconstructed in wavefront reversal through a phase plate is discussed.