Perturbative analysis of photorefractive fundamental space-charge field with phase modulation at large modulation depths

We discuss the kinetics of the photorefractive fundamental space-charge field with phase-modulation at large modulation depth of the interference pattern. When no external field is applied, the influence of large modulation depth on the corrected fundamental space-charge field must be considered at low phase-modulation frequency and at small diffusion field. For the drifted case, the corrected fundamental space-charge field will be changed for various external applied fields at low phase-modulation frequency. As two-wave coupling is not neglected, the corrected fundamental space-charge field will not be in agreement with the case of no two-wave coupling.