Mid-infrared optical parametric oscillator pumped by ahigh-pulse-energy, Q-switched Ho3+:YAG laser

A high-pulse-energy mid-infrared light source is presented, based on a zinc–germanium–phosphide optical parametric oscillator (ZGP OPO) pumped by an actively $Q$-switched high-pulse-energy ${{\rm Ho}^{3 +}}{:}{\rm YAG}$ laser. The ${{\rm Ho}^{3 +}}{:}{\rm YAG}$ pump laser source is capable of generating a pulse energy of 15 mJ from a single ${{\rm Ho}^{3 +}}{:}{\rm YAG}$ rod at room temperature at a pulse repetition frequency (PRF) of 700 Hz. A maximum power of 20.1 W at a central wavelength of 2090 nm can be obtained in continuous operation, with a slope efficiency of 45.1%. A good beam quality with an ${{\rm M}^2}$ better than 1.3 was achieved in $Q$-switched operation. The presented laser architecture was used as a suitable pump source for a ZGP-based OPO. Operated at a PRF of 2 kHz and pumped with a pulse energy of 8 mJ, a low conversion threshold of 1.5 W and a maximum total output power of 6.3 W could be obtained in a linear ZGP-based OPO. At maximum power, the peak power of the generated mid-infrared radiation exceeded 120 kW, while the beam quality was affected by the strong gain lens building inside the nonlinear material as a consequence of the high-energy pump pulses.