The Photorefractive Effect : A Simplified Model

The simplified band transport model of the photorefractive effect in which the material responds linearly to local changes in light intensity modulation ratio (fringe contrast) is examined in detail. The validity of the model for cosinusoidal grating formation is first discussed with reference to spatial frequency and time dependence. The "hopping" model of the photorefractive effect is then considered. It is shown that, although being physically distinct from the band transport model, the hopping model may be considered as a special case of the band transport equations. Results of a numerical simulation of the band transport model are presented which illustrate the validity of the linear in modulation approximation. The band transport model is then extended to describe non-plane wave interactions and include a tensor static permittivity. Features of this extended model are emphasised by some experimental results. These results show the effect of non uniform beam intensity profiles on apparent time constants as measured in four wave mixing experiments using photorefractive Bi12Siqo20