Two-color photorefractive properties in near-stoichiometric lithium tantalate crystals

The two-color photorefractive properties in undoped as-grown near-stoichiometric lithium tantalate crystals were investigated, where a near-infrared laser and a cw ultraviolet beam were used for writing and gating, respectively. The key parameters in characterizing two-color photorefractive effect, light-induced absorption change, two-color sensitivity, refractive index change, readout characteristics, and dark decay were measured by changing intensities of gating and writing beams, wavelengths of gating and writing beams for the crystals with different near-stoichiometric crystal compositions, and proton concentrations. The results showed that there exists an optimal crystal composition of around 49.65% for both sensitivity and refractive index change together with moderate lifetime of small polarons. The achieved refractive index change was on the order of 10−4, and the obtained maximum sensitivity was 0.18 cm/J. The extrapolated lifetime of holograms at room temperature in the crystals without observab...