BaGa₂GeSe₆ nanosecond optical parametric oscillator pumped at 2.05 µm by a Ho:LiLuF₄ laser

We present what we believe is the first laser-driven BaGa₂GeSe₆ (BGGSe) optical parametric oscillator (OPO). Pumped by a nanosecond Ho:LiLuF₄ (Ho:LLF) laser system at 100 Hz in a double pass, the OPO employs a short, singly‑resonant linear cavity, delivering signal and idler radiation within the atmospheric transmission window (between 3.4 and 5.2 µm). The combined output pulse energy of signal and idler exceeds 1.6 mJ, with the signal centered near 3.7 µm and the idler near 4.5 µm. Measured beam‑quality factors satisfy M² < 1.4 for each of the output beams.