2 kW narrow-linewidth Yb-Raman fiber amplifier

In this Letter, we report a high-power narrow-linewidth Yb-Raman fiber amplifier with a high second-order Raman threshold and high intensity stability. By employing two temporally stable seed lasers, over 2 kW output power at 1120 nm is achieved at a pump power of 2.6 kW with an optical-to-optical efficiency of 76.3%. The 3 dB linewidth of the 1120 nm Raman-signal laser varies slightly from 0.41 nm to 0.53 nm, and the power ratio of the second-order Raman Stokes light is only about ${-}{46.3}\;{\rm{dB}}$ at the output power of 2 kW. The results further confirm that the technique of employing temporally stable seed lasers is superior to the power scaling of narrow-linewidth Yb-Raman fiber amplifiers. To the best of our knowledge, it is the first demonstration of an over 2 kW narrow-linewidth fiber laser operating at 1120 nm.