Improvement of photorefractive properties in Hf:Fe:LiNbO₃ crystals with various Li/Nb ratios

Photorefractive properties of Hf:Fe:LiNbO₃ crystals with various Li/Nb ratios have been investigated at 488 nm wavelength based on the two-wave coupling experiment. High diffraction efficiency and large recording sensitivity are observed and explained. The decrease in Li vacancies is suggested to be the main contributor to the increase in the photoconductivity and subsequently to the induction of the improvement of recording sensitivity. The saturation diffraction efficiency is measured up to 80.2%, and simultaneously the recording sensitivity of 0.91 cm/J is achieved to in the Hf:Fe:LiNbO₃ crystal grown from the melt with the Li/Nb ratio of 1.20, which is significantly enhanced as compared with those of the Hf:Fe:LiNbO₃ crystal with the Li/Nb ratio of 0.94 in melt under the same experimental conditions. Experimental results definitely show that increasing the Li/Nb ratio in crystal is an effective method for Hf:Fe:LiNbO₃ crystal to improve its photorefractive properties.