SPATIAL AND TEMPORAL FIDELITY OF PHOTOREFRACTIVE IMAGE CORRELATORS

The set of equations describing photorefractive four-wave mixing beams containing time-varying images has been solved in the presence of dif fraction by a perturbation analysis assuming a strong uniform backward pump and weak conjugate. It was found that, to first order, the ampli tude of the conjugate image is bilinearly related to the amplitudes of the probe and the forward-pump images. An expression for the bilinear kernel was derived with a Green's-function approach. This kernel, whi ch governs the spatial and the temporal bandwidths of the wave-mixing system, is a function of the material parameters, the beam angles, and the crystal length. We found that, when a photorefractive crystal is used to generate the correlation between two images, the result is a d istorted version of the correlation image. Numerical simulations demon strate that the distortion increases if one of the images is moving.