We report a 2 kW all-fiberized Raman fiber amplifier with efficient brightness enhancement based on the graded-index fiber. The maximum power output 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 system using graded-index fiber. An optimized fiber combiner adopting graded-index fiber as the pigtail fiber was 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 power output, the beam quality parameter M2 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.

中文翻译：

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大于 2 kW 的全无源光纤拉曼放大器，具有良好的光束质量

我们报告了一种基于渐变折射率光纤的 2 kW 全光纤拉曼光纤放大器，具有高效的亮度增强功能。最大功率输出高达 2.034 kW，以 1130 nm 为中心，相对于注入泵浦功率的转换效率为 79.35%。据我们所知，这是任何使用渐变折射率光纤的拉曼激光系统获得的最高转换效率。制作了采用渐变折射率光纤作为尾纤的优化光纤合路器，使得纤芯泵浦拉曼光纤放大器中的种子亮度得以保持，进一步提高了放大后输出激光的极限亮度。在最大功率输出时，光束质量参数米2为 2.8，对应于 11.2 的信号泵亮度增强因子。据我们所知，我们在100 W以上的拉曼光纤激光器中获得了最高的亮度增强，在150 W以上的渐变折射率拉曼光纤激光器中光束质量最好。