An analysis of an optimized configuration for phase conjugation and four-wave mixing in cubic photorefractive crystals (such as GaAs and Bi12SiO20) is presented. We obtain an exact solution of the four-wave mixing configuration, and find a wide range of self-oscillation regime.
Here we present four wave mixing configuration as one of the most important methods of generation and explanation of process of generation phase conjugation light the coupled equation was solved by three methods: undepleted pump approximation exact solution and two wave mixing approximation. Although exact solutions can be derived for four-wave mixing, the results are difficult to use because of the complicated transcendental equation involved. Solved the coupled equations and introduce an approximation in which two-wave mixing is the dominant process.
The anisotropic four-wave mixing in the scheme recently proposed by S.I. Stepanov and M.P. Petrov (Opt. Commun. vol.53, p.64-8, 1985) is studied. The main feature of this interaction arrangement is that the same phase hologram (index grating) has opposite contrasts for orthogonally polarized, counterpropagating waves. The coupled nonlinear equations, in the case of transmission and reflection gratings, for the pi /2 photorefractive phase shift are exactly solved, and their properties are discussed in detail. The numerical evidence of the effects of bistability and self-oscillation is included.>
The effects of linear absorption on the degenerate and nondegenerate self-oscillation of a photorefractive phase-conjugate mirror under condition of anisotropic four-wave mixing are considered. The phase conjugation results from nonlinear mixing of two strong undepleted orthogonally polarized counterpropagating pump waves with a probe wave. We consider two types of situation for orthogonally polarized pump beams corresponding to two crystal families: one such as the Bi12SiO20 crystal family (sillenite family) and the other such as the BaTiO3 and strontium barium niobate crystal family. In both of these crystal families the degenerate and nondegenerate self-oscillations are shown to occur in the presence of linear absorption, which tends to increase the value of the coupling coefficient required for self-oscillation. Numerical results are presented that exhibit various features of degenerate and nondegenerate self-oscillation in both crystal families for different values of the phase ϕb of the backward grating.
Stationary four-wave mixing in a shifted photorefractive transmission grating formed in cubic gyrotropic crystals of the 23 symmetry is considered in the case of low contrasts of the original optical interference pattern. Expressions for the transmission and reflection coefficients for the phase conjugation of weak light beams in arbitrarily cut samples are obtained by solving exactly the equations for the coupled waves that include the effects of the natural circular birefringence and the linear birefringence induced by the external field. The conditions for the generation of phase-conjugated waves are determined for the mixing at 633 nm in Bi 12 SiO 20 and Bi 12 SiO 20 samples in the case when the grating vector is parallel to the [110] axis and the incident pump waves propagate in the (001) crystal plane and have arbitrary polarisations.