Photorefractive crystals like LiNbO3, KNbO3 or BaTiO3 are suitable media for frequency degenerate two- and four-wave mixing allowing for amplification and phase conjugation of coherent light beams [1, 2].
DFWM as an useful tool to generate phase conjugate waves has recently been the subject of intensive study. In particular photorefractive crystals such as LiNbO3, KNbO3, BaTiO3 and SBN are widely used[1]. Among the published papers on DFWM most are concerned with backward phase conjugate waves and only a few with forward phase conjugate, waves.[2,3] In both of these papers the intensity of the forward phase conjugate wave has not been investigated. We report here a systematic study of the intensity of forward phase conjugate wave.
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.
We analyze the phase-conjugate reflectivity and the amplification property of cross-polarized four-wave mixing with a photorefractive BaTiO3 crystal in consideration of the pump-beam depletion. The coupled-wave equations of cross-polarized four-wave mixing with ordinary writing beams and an extraordinary reading beam are derived and solved with the grating-integral method. The results of calculations of the reflectivity and the amplification factors will be compared with the result under the undepleted-pumps approximation. In addition, to achieve high conversion efficiency, the optimum conditions for the intensity ratio and the angle configurations of the probe and pump beams are also discussed.