Unlocking superior performance of broadband powerful mid-IR optical parametric amplifiers with a BaGa2GeS6 crystal pumped at 1.24 µm

We report on the development of a tunable (1.5-6.5 µm) femtosecond optical parametric amplifier (OPA) based on a novel, to the best of our knowledge, BaGa₂GeS₆ (BGGS) crystal with a Cr:Forsterite pumping laser. Total conversion efficiency as high as 28% is achieved in a robust two-stage setup resulting in the generation of a 340-µJ 1.67-µm signal and 100-µJ 4.65-µm idler pulses. A 5-optical-cycles 94-fs 6-µm idler pulses are demonstrated with a propriate dispersion compensation by Ge and GaAs plates. An experimental estimate is given for the effective nonlinearity of a BGGS material, which for our nonlinear process reaches 19.5 pm/V for Type II phase matching. The crystal is additionally tested as a final amplifier in a high-energy OPA, where total output reaches 1.2 mJ with more than 40% conversion efficiency. The demonstrated high nonlinearity, high damage threshold, and chemical stability of the polished surface make BGGS crystal an ideal candidate for the development of high-energy OPAs with multi-millijoule pumping lasers.