High-beam-quality 2.1 µm pumped mid-infrared type-II phase-matching BaGa 4 Se 7 optical parametric oscillator with a ZnGeP 2 amplifier.

We firstly demonstrated a tunable 2.1 µm pumped mid-infrared type-II phase-matching B a G a 4 S e 7 (BGSe) optical parametric oscillator (OPO). A signal tuning range of 3.82-3.99 µm was achieved. With a signal light produced by the BGSe OPO serving as seed, the Z n G e P 2 (ZGP) optical parametric amplifier (OPA) was first introduced. A 4.35 W mid-infrared laser was obtained in the novel type-II BGSe OPO with a ZGP OPA system, which was pumped by a 24 W 1 kHz Q -switched Ho:YAG laser. The beam quality factor M 2 of the whole system is ∼2.3, which is over a 50% promotion on the previous M 2 results of single BGSe OPO.