Abstract

A beam reflected from a photorefractive phase conjugate mirror may experience a transverse displacement (lateral shift) and wavefront aberration (longitudinal shift), if a dc electric field is present or if the probe beam is frequency detuned relative to the pumps. These shifts, which can be of the order of several wavelengths for the lateral shift and tens of wavelengths for the longitudinal shift, are a result of the angular dependence of the reflectivity, an effect similar to the Goos-Hanchen effect. The angular dependence of the reflectivity is a spatially dispersive effect arising from the nonlocal nature of the wave interaction. We assume that the incident beam is paraxial and slowly varying in space and represent it as a superposition of plane waves (angular spectrum). The complex reflectivity is then expanded about the beam axis, each plane wave component is multiplied by its complex reflectivity, and added to form the conjugate beam. The linear term in this expansion generates the lateral shift whereas the quadratic term is responsible for the longitudinal shift. Pulsed beams are distorted because they contain harmonic components, each of which undergoes different shifts.

© 1989 Optical Society of America