Shallow Traps Resolve the IX Mystery in Photorefractive Barium Titanate

In 1984 Ducharme and Feinberg1 showed that the speed of the photorefractive effect in barium titanate was not a linear function of the light intensity I, but varied instead as Ix, with x < 1. This sublinear dependence prevailed over four orders of the light intensity ( 0.01 Watt/cm2 <I < 100 Watt/cm2 ). They also showed that the power x increased with increasing temperature. In 1988, Mahgerefteh and Feinberg2 showed that the speed of the photorefractive effect in barium titanate obeyed the same Ix power law for the case of pulsed illumination as well as for cw illumination, even though the peak intensities used in the pulsed case were 104 times that of the cw experiments. This result suggested that the Ix power law was valid for a range spanning eight orders of magnitude in the light intensity.