Fig. 1. Output spectra at near-infrared band of rare-earth-doped lasers^[13]

Fig. 2. Research progress in power scaling of laser based on hybrid Yb-Raman gain

Fig. 3. Experimental setup for 10 kW laser based on hybrid Yb-Raman gain^[14]. (a) Master oscillator power amplifier; (b) backward pumped random Raman fiber laser; (c) ytterbium doped fiber laser seed source; (d) 1018 nm laser module

Fig. 4. Research progress in fiber laser pumped RFL

Fig. 5. Experimental setup of kilowatt-class cladding-pumped RFL^[54]

Fig. 6. Experimental diagram illustrating influence of pump time-frequency characteristics on output characteristics of cladding-pumped Raman fiber lasers^[56]. (a) Random Raman laser; (b) reflection spectrum of grating; (c) refractive index of fiber; (d) input beam profile; (e) output beam profile.

Fig. 7. Schematic of high-power Raman laser based on FBG^[59]

Fig. 8. Structural diagram of GRIN fiber-based Raman oscillator^[64]

Fig. 9. Schematic of 1780 W Raman oscillator based on multimode GRIN fiber and its power spectral characteristics^[16]. (a) Raman oscillator; (b) output power; (c) output spectrum

Fig. 10. Schematic of 4 kW Raman amplifier based on multimode GRIN fiber and its power spectral characteristics^[15]. (a) Raman amplifier; (b) output power; (c) output spectra

Fig. 11. Typical research progress in cascaded Raman fiber lasers

Fig. 12. Schematic diagram of classic five-stage cascaded Raman fiber laser^[102]

Fig. 13. Schematic diagram of first domestic 100-W-level CRFL^[105]

Fig. 14. Schematic diagram of cascaded random Raman fiber laser emitting vortex beam^[111]

Fig. 15. Schematic of first experimental setup for RFL based on LD direct pumping^[118-119]

Fig. 16. Randomly distributed RFL based on spectral beam combining LD direct pumping^[132]. (a) Random Raman laser; (b) spectrum of pump light; (c) reflection spectrum of grating; (d) spectrum of signal light

Fig. 17. Kilowatt-level RFL based on spectral beam combining LD direct pumping^[135]. (a) Raman oscillator; (b) spectrum of pump light; (c) refractive index of fiber; (d) spectrum of signal light