A series of Hf co-doped uranium-doped lithium niobate (LN:U,Hf) crystals with a diameter of one inch were grown by the modified Bridgman method. XPS analysis showed that U ions coexist in mixed valence states of U4+, U5+, and U6+. At 442 nm, LN:U,Hf1.0 exhibited a fast photorefractive response of 0.32 s together with a high saturation diffraction efficiency of 82.01%. With increasing Hf concentration, the optical damage resistance was significantly enhanced, and LN:U,Hf5.0 achieved an optical damage threshold of 2.8 × 105 W/cm2. Two-beam coupling experiments indicated that electrons are the dominant charge carriers and diffusion is the main transport mechanism. It demonstrates that co-doping Hf4+ provides an effective route to simultaneously enhance photorefractive response and optical damage resistance in LN:U, offering potential for high-power and fast-response photonic devices.
Xu et al. (Sat,) studied this question.