Effects of light modulation on grating phase shifts in photorefractive recording

Abstract

Phase mismatches with regard to light of photorefractive gratings have been investigated for arbitrary modulation depths of the illuminating pattern. The time evolution of the phases during recording under an applied field as well as the steady state values have been calculated for various harmonics. A powerful numerical method has been used to solve the band transport model equations. A clear correlation between the oscillations of the phase shift and these for the grating amplitude have been found for low modulation depths m. They both are markedly damped for high m. The steady-state phase mismatch for the fundamental grating increases with m at variance with the linear prediction. This increase together with the superlinear behaviour for the amplitude gives rise to a marked enhancement of the photorefractive coupling coefficients with regard to the linear values.