An analysis is made of two new effects in four-wave wavefront reversal of optical beams by optically induced gratings in resonant media: bistability and diffraction bleaching (Borrmann effect).
A theoretical investigation is made of the characteristics of wavefront reversal in the course of a degenerate four-wave interaction in moving slow-response media. It is shown that the displacement (by a moving medium) of amplitude and phase gratings, and also diffusion of excited particles may influence greatly the parameters of a reversed wave. The characteristics of a nonlinear mechanism of light-induced heat evolution in thermodynamic-nonequilibrium media are determined for spatially inhomogeneous radiation.
A theoretical analysis is made of noncoplanar four-beam Raman–Nath self-diffraction in media with saturable absorption. The mechanisms responsible for the generation of the first- and second-order diffracted beams are identified. The intensities of the diffracted beams not lying in the planes of convergence of the exciting beams can, for certain phase relationships, be considerably higher (by a factor of ~ 102) than the intensities of the beams in these planes. The reason for the dependence of the effectiveness of self-diffraction on phase relationships between the excited beams is interference between elementary diffraction processes in various light-induced gratings.
A theoretical analysis is made of wavefront reversal which is not sensitive to the optical quality of the nonlinear wavefront-reversing medium when complex-conjugate reference waves are formed spontaneously. An investigation is made of the linear and nonlinear stages of reversed wave generation in various nonlinear media using feedback in degenerate and nondegenerate four-wave interaction. It is shown that in nonamplifying nonlinear media this method can only be achieved by additional amplification of the radiation reflected from the nonlinear medium.