Low-threshold mid-infrared ZGP optical parametric oscillator pumped by wavelength-selectable Tm:YLF laser at 1.93 μm

We demonstrated a mid-infrared (MIR) ZGP optical parametric oscillator (OPO) which was pumped by an acousto-optically Q-switched Tm:YLF laser operated at 1.93 μm for the first time. The pump wavelength was realized by only using a low transmission output coupler of 12% at ~ 1.9 μm rather than other wavelength selectors such as VBG. The measured threshold as low as 0.09 MW/cm 2 was achieved for the double-pump-pass, doubly-resonated ZGP OPO with a short double-concave cavity. The low absorption coefficient of the ZGP crystal at 1.93 μm (0.027 cm −1 ) was also helpful to reduce the threshold of ZGP OPO. When the pump power of the pulsed Tm:YLF laser was 9.05 W at 20 kHz, the total output power of the 3.62 μm signal and 4.13 μm idler beams was 3.64 W. The conversion efficiency and slope efficiency were 40.2% and 50.5%, respectively. The presented work offers a new reference for MIR ZGP OPOs with pump wavelengths shorter than 2 μm.