Large modulation effects in photorefractive crystals

A numerical solution to the band transport equations is presented, which is quite general, and predicts the behaviour of photorefractive materials in the saturation limit with a moving grating. The band transport equations are solved by a secular perturbation method, where the perturbation parameter is the fundamental component of the induced space charge field. In this manner, one can predict the form of the space charge field and the charge density distribution at various depths of modulation. The effects of applying an AC field with a square waveform to a static grating are considered and it is shown that there is an upper limit to the degree of enhancement obtainable at any particular depth of modulation