Efficient, sub-4-cycle, 1-µm-pumped optical parametric amplifier at 10  µm based on BaGa₄S₇

We report on a microjoule-scale mid-infrared optical parametric amplifier (OPA) based on the recently developed wide-bandgap orthorhombic crystal, BaGa₄S₇ (BGS) and directly compare its performance to that of LiGaS₂ (LGS) in the same OPA setup. The source is based on a single OPA stage amplifying supercontinuum seed pulses with a quantum efficiency of 29% at an idler wavelength of 10 µm, featuring nominally carrier-envelope phase-stable pulses. As a result of pumping the OPA directly at 1 µm, the overall conversion efficiency far exceeds that of traditional schemes based on OPAs followed by difference frequency generation. Chirp compensation using bulk germanium resulted in 126 fs pulses covering the 7.6-11.5 µm spectral range. BGS holds great promise for power scaling due to its availability in larger single-crystal sizes than LGS.