4.4-μm Raman laser based on hollow-core silica fibre

A Raman laser with a wavelength exceeding 4 μm is designed for the first time. Using a revolver silica fibre with a hollow core filled with molecular hydrogen (¹H₂) as an active medium, we have obtained SRS lasing at a wavelength of 4.4 μm under pumping by a pulsed erbium fibre laser (λ = 1.56 μm, τ = 2 ns). The SRS conversion quantum efficiency reaches 15%, and the maximum output peak power at a wavelength of 4.4 μm is 0.6 kW.