25 W continuous-wave fiber gas Raman laser at 1.9 μm wavelength based on low-loss anti-resonant hollow-core fiber

We report continuous operation of stimulated Raman scattering at 1.9 μm wavelength based on hydrogen-filled antiresonant hollow-core fiber for the first time, to the best of our knowledge. Using a single-frequency fiber laser at 1 μm as the pump source, a maximum of over 25 W Stokes is measured after a single pass in a 47 m nested type of AR-HCF filled with hydrogen gas of 10 bar pressure, corresponding to a slope efficiency of 40 % and a quantum efficiency of 72.5 %. Backward stimulated Raman scattering is observed at the same time and a maximum power of over 5 W is measured at a higher pressure of 30 bar. This work demonstrates the potential of gas-filled AR-HCF in the high power nonlinear wavelength conversion in the mid-infrared spectral region.