Abstract

Cobalt-doped barium titanate was grown and then oxygen-reduced to obtain electron dominated photoconduction. The absorption spectra of the reduced crystals shows a characteristic peak at ~450 nm which is a function of dopant and reduction level. We have characterized the photorefractive properties of these crystals in a 0°-cut orientation, first in the as-grown state, the reduced state, and then the same reduced crystal but fabricated into a 45°-cut orientation. The as- grown and reduced 0°-cut crystals have the same beam-coupling gain but the rise time is faster by a factor of 3 in the reduced crystal. From our measurements of the response time as a function of orientation (0° and 45°-cuts) we infer that there is an increase in the dc dielectric constant seen by the photorefractive grating in the 45°-cut and a nearly equivalent increase in the mobility-lifetime product. This means that the rise time of beam-coupling in the 0° (ordinary polarization) and 45° (extraordinary polarization) orientations are approximately equivalent but the gain is substantially higher in the 45°-cut. The process of doping, reduction and using a 45°-cut gives the highest photorefractive sensitivity reported to date for barium titanate . The Cat (self-pumped phase conjugate) and Kitty (degenerate four-wave mixing) rise times are substantially faster in these crystals and higher than previously reported, with millisecond rise times for the Kitty conjugate with 25 mW of input power for the Cat conjugate. We find that barium titanate can be more sensitive than previously assumed and as sensitive as other photorefractive oxides.

© 1991 Optical Society of America