266 nm generation performance of NSBBF crystal improved by elevating the operating temperature

NaSr₃Be₃B₃O₉F₄ (NSBBF) crystal is a promising nonlinear optical (NLO) crystal for 266 nm ultraviolet (UV) generation by fourth-harmonic generation (FHG), whereas crystal cracking under nanosecond (ns) high-power pumping limits further power scaling. For this purpose, an effective route is analyzed and proposed in this paper that is moderate elevating the operating temperature of NSBBF crystal. When the crystal temperature was set at 100.9 ℃, and under the condition that all other experimental parameters remained unchanged, the output power and conversion efficiency increased by 10.4% and 27.3%, respectively. The conversion efficiency reached 6.07%, which is the highest conversion efficiency achieved by the NSBBF crystal under ns pumping conditions to date. Simultaneously, elevating the operating temperature effectively delayed crystal cracking. Variable-temperature Z-scan measurements revealed that both the nonlinear absorption coefficient (β) and nonlinear refractive index (n₂) decreased significantly with increasing temperature. The reduction in β and n₂ at elevated temperature was consistent with the improved FHG behavior. Meanwhile, under 4 W 532 nm irradiation, the laser-induced temperature rise decreased from approximately 2.8 to 0.5 °C with increasing operating temperature, indicating a weakened laser-induced thermal response at 100.9 ℃. This research provides a valuable technique for the future development of NSBBF crystals in UV laser output.