In this paper, we report a 2-kW all-fiberized Raman fiber amplifier with efficient brightness enhancement based on the graded-index fiber. The maximum output power reaches up to 2.034 kW centered at 1130 nm, with a conversion efficiency of 79.35% with respect to the injected pump power. To the best of our knowledge, this is the highest conversion efficiency obtained for any Raman laser systems using graded-index fiber. An optimized fiber combiner adopting the graded-index fiber as the pigtail fiber is fabricated, enabling the preservation of the seeding brightness in the core-pumped Raman fiber amplifier, and further enhancing the ultimate brightness of the output laser after amplification. At the maximum output power, the beam quality parameter M<sup>2</sup> is 2.8 corresponding to a signal-to-pump brightness enhancement factor of 11.2. As far as we know, we obtain the highest brightness enhancement among Raman fiber lasers of over 100 W, and the best beam quality for graded-index Raman fiber lasers of over 150 W.
Chen Yizhu, Yao Tianfu, Xiao Hu, Leng Jinyong, Zhou Pu. More than 2 kW all-passive fiber Raman amplifier with good beam quality[J]. High Power Laser Science and Engineering, , (): .
