Fig. 1. Experimental setup of the high-power narrow-linewidth fiber laser system.

Fig. 2. SRS and TMI threshold evolution along with the backward-pumped power ratio.

Fig. 3. Spectrum of the seed laser.

Fig. 4. Output powers of the signal laser and backward-propagating laser at different pump power.

Fig. 5. Output spectra of the signal laser at different output power in the main amplifier.

Fig. 6. Spectral width of the signal laser at different output power: (a) spectral width in the logarithmic coordinates; (b) power-ratio spectral width.

Fig. 7. Power ratio of the Raman Stokes light at different output power.

Fig. 8. Output temporal property and beam quality of the signal laser at the maximum output power: (a) normalized intensity evolution; (b) corresponding power spectral density; (c) beam quality.