Vacuum ultraviolet second-harmonic generation in NH₄B₄O₆F crystal

Vacuum ultraviolet (VUV, 100-200 nm) light sources are crucial for advanced spectroscopy, quantum research and semiconductor lithography^1-3. Compared with conventional large-scale VUV generation technologies^4-7, second-harmonic generation (SHG) through nonlinear optical (NLO) crystals^8-10 is the simplest and most efficient method. However, the scarcity of suitable NLO crystals has constrained the production of VUV light through SHG: existing materials fail to meet phase-matching requirements, suffer from low conversion efficiency or have severe growth limitations^11-19. In this study, we report the development of the fluorooxoborate crystal NH₄B₄O₆F (abbreviated as ABF) as a promising material for VUV light generation. VUV devices with specific phase-matching angles were constructed, achieving a record 158.9-nm light through phase-matching SHG and a maximum nanosecond pulse energy of 4.8 mJ at 177.3 nm with a conversion efficiency of 5.9%. The enhanced NLO performance is attributed to optimized arrangements of fluorine-based units creating asymmetric sublattices. This work provides further material in the NLO field, with potential for applications in compact, high-power VUV lasers using ABF.