Theory of amplitude and phase effects in 2-D-two-wave mixing

The two-wave mixing process in a photorefractive medium is investigated including nonuniform amplitude distributions of the pump and signal waves, plane-aberrated phase fronts, absorption, and arbitrary grating phase shift φ. The resulting system of two-dimensional coupled-wave equations is solved numerically with the aid of a two-dimensional Runge-Kutta method. Numerical data are shown to explain the gain distributions and image distortion properties in photorefractive amplifiers of the crossed beam, transmission and reflection grating type. A simple relation is presented describing the amplitude-phase crosstalk in two-wave mixing. One example is illustrated showing the possibility for compensating for aberrations using special pump and/or signal beam profiles with a grating phase shift different from 90°