Towards High-Power Densely Step-Tunable Mid-Infrared Fiber Source From 4.27 to 4.43 µm in CO_2-Filled Anti-Resonant Hollow-Core Silica Fibers

Soft-glass fiber lasers have attracted lots of attentions as they are most likely to achieve compact, stable, and highly efficient mid-infrared emission, which has unique applications in many fields. However, due to the immature manufacturing technique of soft glass fibers and the limited types of doped rear-earth, laser power enhancing and wavelength expansion beyond 4 μm are greatly restricted. Gas-filled hollow-core fibers (HCFs) have been proved to be an effective way to generate mid-infrared emission. We previously demonstrated a continuous-wave 4.3 μm fiber source with power of 82 mW in CO₂-filled HCFs. Here, the maximum output power is increased to 557 mW, and laser wavelengths densely step-tunable from 4276 to 4428 nm including 46 lines have been demonstrated. The output spectrum and power properties with gas pressure and pump power are investigated in detail. In addition, the influence of buffer gases on laser characteristics is studied experimentally for the first time. This work provides significant guidance for the development of high-power tunable mid-infrared fiber gas lasers.