Cycle-dependent degradation of second-harmonic generation characteristics in CsLiB ₆ O ₁₀ associated with the reabsorption of water impurities

We investigated the effects of reabsorption of water impurities on the second-harmonic generation (SHG) characteristics of CsLiB ₆ O ₁₀ (CLBO) crystal and found that repeated reabsorption and desorption cycles of water impurities lead to degradation of SH output. Raman spectroscopy revealed that heat treatment at 150 °C after reabsorption induces the diffusion of H ₂ O molecules, which were initially localized at the crystal surface, into the crystal interior, suggesting the formation of defect precursors during this process. In addition, based on numerical simulations of SHG, we considered that defect accumulation associated with these cycles contributes to increased ultraviolet absorption and subsequent output degradation. These results indicate that suppressing water reabsorption is essential for achieving stable operation of CLBO-based high-power deep-ultraviolet laser sources.