The possibility to perform time-resolved spectroscopic studies in the molecular fingerprinting region or extending the cutoff wavelength of high-harmonic generation has recently boosted the development of efficient mid-infrared (mid-IR) ultrafast lasers. In particular, fiber lasers based on active media such as thulium or holmium are a very active area of research since they are robust, compact, and can operate at high repetition rates. These systems, however, are still complex, are unable to deliver pulses shorter than 100 fs, and are not yet as mature as their near-infrared counterparts. Here, we report the generation of sub-40 fs pulses at 1.8 µm, with quantum efficiencies of 50% and without the need for post-compression, in hydrogen-filled, hollow-core photonic crystal fiber pumped by a commercial high-repetition-rate 300 fs fiber laser at 1030 nm. This is achieved by pressure-tuning the dispersion and avoiding Raman gain suppression by adjusting the chirp of the pump pulses and the proportion of higher-order modes launched into the fiber. The system is optimized using a physical model that incorporates the main linear and nonlinear contributions to the optical response. The approach is average power-scalable, permits adjustment of the pulse shape, and can potentially allow access to much longer wavelengths.

中文翻译：

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通过chi辅助拉曼散射在充氢的中空光纤中以40 µs的脉冲以1.8 µm和MHz的重复频率产生亚40 fs脉冲

最近，在分子指纹区进行时间分辨光谱研究或扩展高谐波产生的截止波长的可能性促进了高效中红外（mid-IR）超快激光器的发展。尤其是，基于活性介质（例如th或）的光纤激光器非常坚固，紧凑，并且可以高重复频率运行，因此是非常活跃的研究领域。但是，这些系统仍然很复杂，无法传送短于100 fs的脉冲，并且还不如近红外系统成熟。在这里，我们报告了在充满氢气的情况下，在1.8 µm处产生了小于40 fs的脉冲，量子效率为50％，并且不需要后压缩。中空光子晶体光纤由商用高重复频率300 fs光纤激光器在1030 nm处泵浦。这可以通过对色散进行压力调整并通过调整泵浦脉冲的线性调频脉冲和引入光纤的高阶模的比例来避免拉曼增益抑制来实现。该系统使用物理模型进行了优化，该模型将对光学响应的​​主要线性和非线性贡献结合在一起。该方法是平均功率可缩放的，允许调整脉冲形状，并可能允许访问更长的波长。该系统使用物理模型进行了优化，该模型将对光学响应的​​主要线性和非线性贡献结合在一起。该方法是平均功率可缩放的，允许调整脉冲形状，并可能允许访问更长的波长。该系统使用物理模型进行了优化，该模型将对光学响应的​​主要线性和非线性贡献结合在一起。该方法是平均功率可缩放的，允许调整脉冲形状，并可能允许访问更长的波长。