Abstract

Because of their large nonlinearities, photorefractive materials are useful for a variety of applications. C3:BaTiO₃ is a NEW photorefractive crystal which was successfully grown with good optical quality and different doping cerium concentrations at our Institute for the first time in 1992. It has superior photorefractive properties when compared with the common photorefractive materials. In these crystals the formation of a self-pumped phase conjugate (SPEC) wave is based on the backward stimulated photorefractive scattering in air and in the absence of an external seed beam. This is different from total-intemal-reflection SPPC (Cat mirror). We obtained high SPPC reflectivities in a large incident angle range in 0°-cut and 45°-cut crystals. Even if the incident angles are negative, SPPC wave still has high reflectivity which can be observed only in Ce:BaTiO₃ to our knowledge. The dependence of SPPC reflectivity on the different wavelengths has been studied. Over 50% SPPC reflectivities with the wavelengths ranging from 488 nm to 780 nm are obtained. The reflectivities of 85%, 86.8% and 77% were achieved at λ = 730 nm, λ = 633 nm and λ = 515 nm, respectively. We also studied the SPPC reflectivities as a function of the position X of the incident laser beam upon the crystal entrance face (100). It indicates that the SPPC reflectivities are larger than 60%, while the position X is shifted in a range of 5 mm (from 2 mm to 7 mm) along the c direction (8 mm). Thus the SPPC reflectivity is highly insensitive to incident beam's angle, inclination, and pitch relative to the crystal. This makes obtainment of the SPPC wave easy. Fidelity of phase conjugate image by backward stimulated photorefractive scattering without and with an aberrator has comparable resolution, as such 313 line pairs/mm. Coupling constant of two-wave mixing is larger than 40 cm⁻¹. Estimated photorefractive charge densities ranged from 1 ~ 2 × 10¹⁷ cm⁻³. The Electro-Optic coefficients r₄₂ and r₁₃ in Ce: BaTiO₃ crystals are one and a half as high as undoped BaTiO₃ crystal. Thus, this crystal is more attractive for use in practical devices and applications.

© 1995 IEEE