Temporal and spatial evolution of beam coupling in two-wave mixing under an applied electric field was calculated numerically for bismuth silicon oxide. A new and powerful method to calculate the intensities of the two light beams interacting along the crystal during grating formation was developed. To accomplish this modeling the band transport model at both low and high modulation depths was solved to obtain the temporal evolution of the space charge field and the phase mismatch of photorefractive grating with regard to light illumination pattern. These quantities were used to calculate the coupling gain coefficients required to solve also numerically the coupling equations governing the energy exchange between the beams intensities traveling through the crystal. An unusual non-monotonous effect on time evolution of the intensities of light beam was observed. The intensities show an anomalous variation before to attain its steady state level.

© 2001 Optical Society of America

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