Photorefractive properties of lithium and copper in-diffused lithium niobate crystals

Abstract

Near-stoichiometric copper-doped lithium niobate crystals are fabricated by in-diffusion of thin layers of evaporated copper and a subsequent vapor transport equilibration treatment. The crystals are heated in a Li-rich atmosphere to increase the Li content. To determine the photorefractive properties, holographic as well as electrical measurements are performed. Saturation values of the refractive-index changes ΔnS, bulk photovoltaic current densities jphv, photoconductivities σph, and holographic sensitivities S are measured for light intensities up to 104 W/m2. Comparison with experimental data of congruent crystals indicates that the specific photoconductivity is 15 times larger after a vapor transport equilibration treatment. The specific bulk photovoltaic coefficient β* is 2 times larger, refractive-index changes are 7 times smaller, and the holographic sensitivity is up to 4 times larger.