Tandem pumping is a promising technique for gaining higher power from ytterbium-doped fiber (YDF) lasers. However, the characteristics of tandem pumped laser light, especially their variation with the lasing wavelengths, were not thoroughly investigated. We investigated the characteristics with the first 1018-nm tandem-pumped high-power tunable YDF laser. The 1018-nm tandem pumping was not applicable in tunable fiber lasers before because its much-lower absorption requires compensation of long YDFs, which enhances destructive nonlinear effects as a barrel effect for tuning wavelengths. Here, the setup used a fiber ring-cavity as seed, which was much more cost-effective than conventional setups, and only three stages of amplification, of which the last stage was unidirectional tandem-pumped. By deliberate system design, it gained over 1-kW output powers at wavelengths tuning from 1060–1090 nm with ∼100-pm 3 dB linewidths and 79.4%∼85.6% slope efficiencies. Amplified spontaneous emissions (ASE) and stimulated Brillouin scattering (SBS) caused no limits for further scaling powers. Variations of spectra and beam qualities of the outputs with the tuning wavelengths were revealed in detail in the experiment. Drastically varying linewidths at ∼1062 and ∼1080 nm suggested complex evolution of the nonlinear effects with the pump light. This study offers not only an economic seed setup to high-power narrow-linewidth tunable fiber lasers, but detailed characteristics of laser amplified with 1018-nm pump in YDFs. The knowledge of the characteristics can usefully guide future design of high-performance tandem-pumped fiber lasers.

中文翻译：

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串联泵浦高功率窄线宽光纤激光器可调谐范围为 1060 至 1090 nm

串联泵浦是一种从掺镱光纤 (YDF) 激光器获得更高功率的有前途的技术。然而，串联泵浦激光的特性，特别是它们随激光波长的变化，没有得到彻底的研究。我们研究了第一台 1018 nm 串联泵浦高功率可调谐 YDF 激光器的特性。1018 nm 串联泵浦以前不适用于可调谐光纤激光器，因为其低得多的吸收需要对长 YDF 进行补偿，这增强了破坏性非线性效应，作为调谐波长的桶效应。在这里，该设置使用光纤环腔作为种子，这比传统设置更具成本效益，并且只有三级放大，其中最后一级是单向串联泵浦。通过刻意的系统设计，它在 1060-1090 nm 的波长调谐下获得了超过 1 kW 的输出功率，具有 ~100-pm 3 dB 线宽和 79.4% ~ 85.6% 的斜率效率。放大的自发辐射 (ASE) 和受激布里渊散射 (SBS) 对进一步缩放功率没有限制。实验中详细揭示了输出的光谱和光束质量随调谐波长的变化。在~1062 和~1080 nm 处急剧变化的线宽表明非线性效应与泵浦光的复杂演变。这项研究不仅为高功率窄线宽可调谐光纤激光器提供了一种经济的种子设置，而且还提供了在 YDF 中用 1018 nm 泵浦放大的激光的详细特性。对这些特性的了解可以有效地指导高性能串联泵浦光纤激光器的未来设计。