We studied the UV photorefractive effect and other optical properties of Na<sup>+</sup>-doped lithium niobate crystals. The behavior of the photorefractive resistance in Na<sup>+</sup>-doped lithium niobate crystals was found to be quite different from that in lithium niobate crystals doped with other well known optical-damage resistant metal ions, such as Mg<sup>2+</sup>, Zn<sup>2+</sup>, In<sup>3+</sup> etc. It is also found that not only the defect structures but also the ratio of [Li]/[Nb] in our samples was changed by doping with Na<sup>+</sup> ions. We theoretically analysed our experimental results, based on the Li-vacancy model.

© 2001 Optical Society of America

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