2-BEAM COUPLING AND RESPONSE-TIME MEASUREMENTS IN BARIUM-TITANATE USING HIGH-INTENSITY LASER-PULSES

We present results of high-intensity measurements of the two-beam coupling gain coefficient and the photorefractive grating response time in barium titanate (BaTiO3). For hole-dominated BaTiO3 the gain coefficient is observed to decrease with intensity in the megawatt-per-square-centimeter range, because of intensity-dependent photocarrier competition, and is also seen to reverse signs above a critical intensity determined by the crystal doping. Significant two-beam coupling is observed to develop transiently during a single pulse of 15-ns duration. An analytical theory, valid at high intensity, is developed that includes the effects of simultaneous electron and hole photoconductivities and carrier saturation. The analysis predicts the experimentally observed strong intensity dependence in the two-beam coupling gain coefficient, including its reversal in sign.