Phase relationships in the case of a four-wave interaction in a photorefractive medium in which a reflection grating is recorded

Derivation is given of relationships for determination of the complex amplitudes of waves interacting in a four-wave mixing process in a photorefractive crystal in which a reflection grating is recorded throughout the whole interaction zone. An analysis is made of the amplitude and phase of a nonlinear reflection coefficient. The role of the real and imaginary parts of the coupling constant in the appearance of multivalued solutions is identified.