Compact High-Energy High-Beam-Quality Long-Wave Infrared BGSe-OPO

Existing long-wave infrared (LWIR) BaGa4Se7 optical parametric oscillators (BGSe-OPOs) adopt linear-cavity configurations yet struggle to balance high beam quality and high output energy. To overcome this limitation, we report a compact Type I phase-matched ring cavity BGSe-OPO pumped by a 1.06 μm laser. Operating at 8.5 μm, the OPO generates 1.2 mJ single pulses with a peak power of 0.25 MW and an optical-to-optical conversion efficiency of 2%. The estimated beam quality factor M2 is 9, representing a threefold enhancement relative to linear-cavity under identical pump conditions. The system features a compact footprint of 400 × 200 mm2 and a far-field divergence angle of 4 mrad after 6× beam expansion, enabling practical applications in far-field monitoring.