Fig. 1. Schematics of experimental setup and principle. (a) Experimental setup diagram. Inset is schematic of hollow-core photonic crystal fiber’s cross section; (b) schematic of energy level transition of first-order rotating Raman of deuterium gas; (c) measured transmission spectrum of hollow-core photonic crystal fiber; (d) spectrum of pump laser at maximum output power

Fig. 2. Output spectrum at 2 MPa in hollow-core photonic crystal fiber (left inset is near-field spot of 1540-nm pump laser; right inset is near-field spot of 1645-nm Raman laser)

Fig. 3. Characteristics of output power. (a) Raman power as a function of pump power at different gas pressures; (b) maximum Raman conversion efficiency (Raman power/total pump power) as a function of pump power at different gas pressures; (c) residual pump power as a function of pump power; (d) Raman power curve at 2-MPa gas pressure

Fig. 4. Pulse and its time-domain characteristics. (a) Pulse shapes of pump laser, Raman laser, and residual pump laser at maximum pump power; (b) measurement of repetition rate of Raman laser