INTENSITY-DEPENDENT HOLE ELECTRON COMPETITION AND PHOTOCARRIER SATURATION IN BATIO3 WHEN USING INTENSE LASER-PULSES

The photorefractive effect in barium titanate (BaTiO3) under high-intensity illumination is modeled. The analysis considers both photocarrier saturation due to strong photoionization and a consequent intensity-dependent change in the relative contributions of hole and electron conductivity. An expression for the exact solution of the space-charge field under high-intensity illumination is presented for photorefractive media with both hole and electron conductivity. In the case of BaTiO3, the intensity dependence of the hole-electron competition arises from an effective increase in hole trapping sites (and electron photoionizing centers), which is due to a large photoionized carrier population. The model explains experimental results in which a crystal that is hole dominated at low intensity is converted into electron-dominated photoconductivity at high intensities when using nanosecond pulse illumination.