Nonlinear vectorial degenerate four-wave mixing in isotropic saturable gain-media

The polarization dependence of degenerate four-wave mixing for isotropic saturable gain media is theoretically and numerically studied. The weak-probe limit is no longer needed in our model for developing nonlinear vectorial coupled-wave equations for the interacting beams. Discrepancy between the two models is presented. It is found that, by comparison with our model, the weak-probe-limit model is no longer valid when the fluence of the pump beams approaches the saturation fluence of the material or the fluence of the probe beam exceeds one-tenth that of the pump beams. The results also show that switching occurs between the transmission and reflection gratings when the forward pump fluence is changed.