Growth and photorefractive properties of an Fe-doped near-stoichiometric LiNbO3 crystal

A near-stoichiometric LiNbO3 crystal with 0.02 wt% Fe2O3 doping was grown from a Li-rich melt (Li/Nb = 1.38, atomic ratio) by the Czochralski method in air atmosphere. The OH- absorption band was characterized by infrared transmittance spectra. The appearance of the 3466 cm-1 absorption band (2.89 mum) manifests that the composition of the grown crystal is close to the stoichiometric ratio. The photorefractive properties were measured by a two-wave coupling experiment. The measured results show that the Fe-doped near-stoichiometric LiNbO3 crystal has a larger exponential gain coefficient than the Fe-doped congruent LiNbO3 crystal. The remarkable gain can be attributed to the photovoltaic field being comparable with the effective limiting space-charge field.