  By focusing on a typical emitting wavelength of 1120 nm as an example, we
present the first demonstration of a high-efficiency, narrow-linewidth
kilowatt-level all-fiber amplifier based on hybrid ytterbium-Raman (Yb-Raman)
gains. Notably, two temporally stable, phase-modulated single-frequency lasers
operating at 1064 nm and 1120nm, respectively, were applied in the fiber
amplifier, to alleviate the spectral broadening of the 1120 signal laser and
suppress the stimulated Brillouin scattering (SBS) effect simultaneously. Over
1 kW narrow-linewidth 1120 nm signal laser was obtained with a slope efficiency
of ~ 77% and a beam quality of M2~1.21. The amplified spontaneous emission
(ASE) noise in the fiber amplifier was effectively suppressed by incorporating
an ASE-filtering system between the seed laser and the main amplifier. Further
examination of the influence of power ratios between the two seed lasers on the
conversion efficiency had proved that the presented amplifier could work
efficiently when the power ratio of 1120 nm seed laser ranged from 31% to 61%.
Overall, this setup could provide a well reference for obtaining high power
narrow-linewidth fiber lasers operating within 1100-1200 nm.
