Fig. 1. Simulation results. (a) Power curves under different fiber lengths (Raman gain is 0.26 cm·GW^-1); (b) power curves under different Raman gains (fiber length is 3.2 m)

Fig. 2. Experimental setup

Fig. 3. Measured transmission losses of hollow-core fiber

Fig. 4. Spectra. (a) Output spectrum of HC-PCF at 0.6 MPa pressure; fine spectra of (b) 1550 nm pump laser and (c) 1705 nm Raman laser

Fig. 5. Time domain diagram of output signal. (a) Repetition frequency of Raman signal at 1.2 MPa pressure; (b) pulse shapes of Raman signal and residual pump light at 1.2 MPa pressure under maximum power output

Fig. 6. Output powers under different pump powers and hydrogen pressures. (a) Raman light power versus pump power at different pressures; (b) residual pump power versus pump power at different pressures; (c) Raman power and residual pump power versus pump power under 1.2 MPa pressure