A high-power monolithic continuous-wave fiber amplifier at 1064 nm has been demonstrated based on a piece of confined ytterbium-doped fiber, which generated 3.5 kW narrow-linewidth laser with near-diffraction-limited beam quality. By tailoring the diameter of gain dopant across the fiber core, and optimizing the profile of refractive index and doping concentration, the confined doping fiber works making the fundamental mode more dominant in transverse mode competition, while suppressing the high-order mode. In a kilowatt-level narrow-linewidth fiber master oscillator power amplifier (MOPA) system, the threshold of mode instability (MI) is about 2.2 times as much as that of the conventional fiber amplifier. Then, by increasing seed power and utilizing a MOPA configuration with four amplifier stages, up to 3.57 kW signal output, a slope efficiency of 61% without any sign of MI or stimulated Raman scattering for a spectral dynamic range of higher than ${-}{{50}}\;{\rm{dB}}$ is obtained. A further increase of the output power was only limited by the available laser-diode pump power. To the best of our knowledge, this is the highest narrow-linewidth laser power generated from the confined doping monolithic fiber amplifier.

中文翻译：

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3.5 kW 窄线宽单片光纤放大器，波长为 1064 nm，采用受限掺杂光纤

已经基于一段受限的掺镱光纤展示了 1064 nm 的高功率单片连续波光纤放大器，该光纤产生了 3.5 kW 窄线宽激光器，光束质量接近衍射极限。通过调整光纤纤芯中增益掺杂剂的直径，优化折射率分布和掺杂浓度，受限掺杂光纤的作用是使基模在横模竞争中占主导地位，同时抑制高阶模。在千瓦级窄线宽光纤主振荡器功率放大器（MOPA）系统中，模式不稳定性（MI）阈值约为传统光纤放大器的2.2倍。然后，通过增加种子功率并利用具有四个放大器级的 MOPA 配置，高达 3.57 kW 的信号输出，${-}{{50}}\;{\rm{dB}}$得到。输出功率的进一步增加仅受可用激光二极管泵浦功率的限制。据我们所知，这是受限掺杂单片光纤放大器产生的最高窄线宽激光功率。