4.4 μm Raman laser based on hydrogen-filled hollow-core silica fiber

4.4 μm Raman laser based on silica fiber is realized for the first time. H2-filled hollow-core silica fiber is used as an active medium. Pumped by high-power 1.56 μm Er-doped fiber laser, the Raman laser generates up to 0.6 kW of peak power at 4.4 μm with quantum conversion efficiency up to 15%.