Reactive Atmosphere Processing of BaTiO(3) and Origins of Its Photorefractive Effect

Abstract : Photorefractive materials offer great promise for applications in optical data processing and phase conjugation using degenerate four-wave mixing. BaTiO3 is a particularly promising material, primarily because the very large value of the electro-optic tensor component r42 yields correspondingly large values of grating efficiency, beam coupling gain, and four-wave mixing reflectivity. Unfortunately, the commercial availability of BaTiO3 crystals is limited, and samples which are available are relatively small and impure and have not been characterized or optimized for photorefractive applications. In the program reviewed here, we have addressed two of the most important problems in the development and use of photorefractive BaTiO3: stabilization of the cubic phase in order to permit more rapid crystal growth than is now possible, and determination and characterization of the photorefractive species in commercial BaTiO3. The second major effort of this program was the identification and characterization of the photorefractive species in BaTiO3. Using the results of a number of experiments, we have concluded that iron (in the forms Fe2+ and Fe3+) is the dominant photorefractive species in commercial BaTiO3. We have been able to measure the densities of Fe2+ and Fe3+, along with the sign of the photocarriers, the effective electro-optic coefficient, and a lumped parameter taking into account the transport properties of holes and electrons.