Improvement of the photorefractive responsive time and optical damage resistance of LiNbO3 by co-doping with uranium and magnesium

A series of uranium and magnesium co-doped LN crystals (LN: U, Mg) were successfully grown using the modified vertical Bridgman method. At 532 nm, the response time of LN: U, Mg was approximately 2 s. The saturated diffraction efficiency, refractive index modulation, and sensitivity decreased first and then increased with the enhanced MgO doping concentration. The electron was the dominant carrier, and the diffusion was the main migration mechanism. When co-doped with 7 mol% MgO, the optical damage threshold of LN: U was significantly improved to be as high as 2.36 × 10⁵ W/cm². The result of the OH⁻ spectrum showed that only 7 mol% exceeded the real threshold concentration of MgO in LN: U, which is consistent with the calculated result based on the Li-vacancy model. In addition, the photorefractive centers and optical damage were also discussed.