High-efficiency all-fiber Raman fiber amplifier with record output power

We demonstrate a high-power, high-efficiency all-fiberized Raman fiber amplifier. The system is established on a master oscillator power amplifier configuration. The signal laser is a fiber oscillator operating at 1060nm, while multiple channels of fiber lasers at 1018nm work as the pump source. By amplifying in a piece of graded-index fiber, the output power of 1060nm reaches 528.8 W at maximum, with an optical-to-optical efficiency of 78.8%. The beam parameter M-2 increases from 10.4 to 4.2 through the stokes shift in the Raman fiber, with a corresponding brightness enhancement of about 3.85, which verifies the Raman beam cleanup in the multimode graded-index fiber. To the best of our knowledge, this is the highest-power all-fiber Raman amplifier reported with a brightness enhancement.