Widely tunable mid-IR BaGa4Se7 optical parametric oscillator pumped at 1064 nm with a three-mirror ring cavity

We report a widely tunable mid-infrared optical parametric oscillator (OPO) with a three-mirror ring cavity configuration. The pump source is a compact 1064 nm Nd:YAG laser oscillator, side-pumped by a quasi-continuous-wave (QCW) 808 nm laser diode array (LDA). Utilizing a KDP electro-optic Q-switch, it delivers pulses with an energy exceeding 70mJ and a duration of 15 ns. The OPO is configured as a singly resonant oscillator with a large-aperture BaGa 4 Se 7 (BGSe) crystal. Using two BGSe crystals enables a continuous tuning range from 3 to 14 μm, while a third crystal is incorporated for comparative analysis of different phase-matching schemes. We obtained maximum single-pulse energies of 4mJ at 3.5 μm and 2.93mJ at 7.4 μm, with the pulse duration ∼ 12 ns. Specifically, at 4.7 μm, the OPO generates an output energy of 3.92mJ with measured beam quality factors of M x 2 = 4.73 and M y 2 = 2.74. This architecture enables the development of high-energy tunable mid-IR coherent sources with good beam quality.