Efficient middle-infrared ZGP-OPO pumped by a Q-switched Ho:LuAG laser with the orthogonally polarized pump recycling scheme.

We describe an efficient middle-infrared laser source based on the Tm:YLF-Ho:LuAG-ZnGeP system in this paper. A new orthogonally polarized recycling pump scheme with a simple thin-film polarizer and a half-wave plate are used in a Ho:LuAG laser. Under an incident pump power of 63.8 W, we achieve a maximum continuous wave output power of 35.7 W in the Ho:LuAG laser, corresponding to a slope efficiency of 60.4% and an optical-to-optical efficiency of 56.0%. With the Q-switched mode, maximum average output powers of 34.1 W, 34.9 W, and 35.2 W were achieved in the Ho:LuAG laser with pulse repetition frequencies of 10 kHz, 15 kHz, and 20 kHz, respectively. With a Ho pump power of 34.1 W, maximum average output powers of 16.7 W, 15.3 W, and 12.6 W were achieved in a middle-infrared zinc germanium phosphide optical parametric oscillator (ZGP-OPO) under pulse repetition frequencies of 10 kHz, 15 kHz, and 20 kHz, respectively. The evaluated beam quality factor M of the ZGP-OPO was 2.2 for the signal and 1.9 for the idler. To the authors' best knowledge, this is the best performance reported for a middle-infrared ZGP-OPO pumped by a Ho:LuAG laser.