Investigation of Increased Photorefractive Damage Resistance in LiNbO3 by Two-Wave Mixing Measurements

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Abstract
The increase in photorefractive damage resistance in both MgO-doped and nondoped Li-deficient LiNbO3 is studied by two wave mixing measurements. Holographic diffraction measurements demonstrated that crystals with high optical damage resistance increase photoconductivity and response time for erasing photorefractive grating. The erasure speed is linearly proportional to the MgO dopant and Li-site vacancy concentrations. The erasure time of holographic grating shows an Arrhenius dependence on temperature from which activation energy is obtained. We proposed an energy level model of the light-induced transport for LiNbO3:MgO dopants introduce donor levels 0.11 eV below the conduction band, whereas, Li-site vacancies in nondoped crystal introduce acceptor levels 0.29–0.44 eV above the valence band.