Continuous-wave long-wavelength infrared difference-frequency generation in ZGP driven by near-infrared fiber lasers

We report the continuous-wave (cw) difference-frequency generation (DFG) in a ZnGeP₂ (ZGP) crystal that produces tunable long-wavelength infrared (LWIR) lasing. Particularly, we experimentally demonstrate the feasibility to drive DFG in ZGP by all-fiber near-infrared fiber lasers consisting of a 1.3 µm tunable cw random Raman fiber laser (RRFL) and a 1.5 µm erbium-doped fiber amplifier seeded by a tunable distributed feedback (DFB) laser, making the whole system compact and robust. As a result, the demonstrated LWIR DFG presents a broadband spectral tuning range spanning from 9.5 to 11.5 µm, and the output powers in the spectral range of 9.5-11 µm are larger than 40 µW pumped by watt-level fiber lasers. Meanwhile, as a typical application, a proof-of-concept demonstration of gas sensing of SF₆ is executed based on the generated cw LWIR source. Our work demonstrates that the combination of ZGP crystal and fiber lasers can provide an effective and robust approach for the generation of cw LWIR radiation with useful power and broadband wavelength tunability.