Transient phase conjugation In photorefractive materials

Abstract

A frequency domain technique is used to determine the response of a photorefractive phase conjugator to a pulsed probe wave. This approach provides a useful analysis of many phenomena involving planar and nonplanar fields. The transient solution to a linearized set of equations that contains contributions from both the transmission and reflection gratings is expressed as a spatiotemporal transfer function that relates the conjugate and probe waves. Associated with this frequency domain solution is a point-spread impulseresponse function that describes how an input delta function in both time and space is distorted by the nonideal conjugation process. Numerical results show the presence of temporal ringing in the conjugate signal if the conjugator is operated near an instability. This implies that the transfer function exhibits resonances for characteristic spatial and temporal frequencies which may be controlled by an external electric field. The ability to control the resonance structure and the amount of ringing in the conjugate signal at different spatial frequencies has a number of useful applications that are reviewed. Solutions based on the fully nonlinear equations are also discussed with emphasis on how the additional nonlinear effects change the linearized stability condition.