Photorefractive properties of SBN:60 systematically doped with rhodium

Abstract

Strontium barium niobate (SBN) was doped with rhodium to enhance its photorefractive behavior. Crystals with six different Rh concentrations, ranging from 0.015 to 0.20 wt. %, were grown and characterized. With a higher Rh concentration the following trends were observed at a wavelength of 514.5 nm: (i) a larger linear absorption coefficient α, (ii) a larger maximum two-beam-coupling coefficient Γ, (iii) a higher net coupling coefficient (Γ − α), (iv) a longer two-beam-coupling time response, (v) a shorter fixed-level-gain time response, (vi) a constant photoionization cross section, and (vii) a smaller photorefractive sensitivity. With extraordinary polarization used to invoke the large r33 electro-optic coefficient, two-beam-coupling coefficients exceeding 60 cm−1 were measured in thin (∼1 mm) plates of the heavily Rh-doped crystals, which is consistent with the expected coupling by inference from measurements with ordinary polarization in thick (∼5 mm) crystals. Contradirectional two-beam coupling in SBN along the ĉ axis (independent of polarization, since r13 = r23) gave a coupling coefficient of almost 14 cm−1 for the 0.20-wt. % sample; the contradirectional coupling coefficient decreased approximately in proportion with the decreasing Rh-doping concentration in the other crystals. Estimated photorefractive charge densities ranged from ∼4 × 1016 to ∼8 × 1017 cm3, which constituted approximately 1% of the total Rh-doping concentration.