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

We report on a {\mu}J-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 {\mu}m, featuring nominally carrier-envelope phase-stable pulses. As a result of pumping the OPA directly at 1 {\mu}m, the overall conversion efficiency far exceeds that of traditional schemes based on OPA's followed by difference frequency generation. Chirp compensation using bulk germanium resulted in 126-fs pulses covering the 7.6-11.5-{\mu}m spectral range. BGS holds great promise for power scaling due to its availability in larger single-crystal sizes than LGS.