Photorefractive properties of LiNbO3 crystals doped by copper diffusion

Lithium niobate volume crystals (up to 1 mm thick) are doped by indiffusion of thin layers of evaporated copper. The obtained samples are investigated by conventional electrical and holographic methods. Saturation values Delta n(s) of the refractive-index changes, bulk-photovoltaic current densities j(phv), and photoconductivities sigma(ph) are measured utilizing samples with copper concentrations in the range (2.2-145) X 10(24) m(-3). Comparison with experimental data for melt-doped lithium niobate shows that the photorefractive properties do not depend on the doping technique. Another important outcome is that the refractive-index changes saturate at 7 x 10(-4) (ordinary light polarization, green light) for copper concentrations larger;than 60 X 10(24) m(-3) This is caused by a strong increase of the photoconductivity for high doping levels.