Highly Efficient, Widely Tunable Femtosecond Optical Parametric Amplifiers Based on BaGa4Se7 Crystal

We present an optical parametric amplifier (OPA), pumped by an Yb fiber laser system, for efficiently generating mid-infrared femtosecond optical pulses over a wide wavelength tuning range of 3.5- $16~\mu $ m. Our scheme starts with two cascaded BBO OPA stages for providing high-power pulses at 1.09- $1.47~\mu $ m with ~200 fs pulse duration, which are used as the seed source for a subsequent mid-infrared OPA based on a BaGa4Se7 (BGSe) crystal. Therefore, with a moderate parametric gain of 4-6 from the final-stage BGSe OPA, a quantum conversion efficiency of higher than 24% is obtained for the mid-infrared idler wave over the full wavelength tuning range at 3.5- $16~\mu $ m. We expect that the source would be useful for applications in mid-infrared spectroscopy.