Phase conjugation by diffraction gratings in photorefractive crystals

Here we present four wave mixing configuration as one of the most important methods of generation and explanation of process of generation phase conjugation tight 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.