266 nm ultraviolet light generation in Ga-doped BaAlBO₃F₂ crystals.

BaAlBO₃F₂ (BABF) crystals are a recently developed and promising nonlinear optical material, notably for the third harmonic generation of ultraviolet (UV) light at 355 nm. However, the fourth harmonic generation of UV light at 266 nm has never been obtained by using a BABF crystal due to its relatively small birefringence. We demonstrate that the birefringence of BABF can be effectively increased by doping it with Ga³⁺. The fourth harmonic generation of UV light at 266 nm was achieved for the first time in a Ga-doped BABF crystal.