Vacuum-ultraviolet (VUV) light is critical for the study of molecules and materials, but the generation of femtosecond pulses in the VUV region at high repetition rates has proven difficult. Here we demonstrate the efficient generation of VUV light at megahertz repetition rates using highly cascaded four-wave mixing processes in a negative-curvature hollow-core fiber. Both even- and odd-order harmonics are generated up to the 15th harmonic (69 nm, 18.0 eV), with high energy resolution of ${\sim}{{40}}\;{\rm{meV}}$. In contrast to direct high harmonic generation, this highly cascaded harmonic generation process requires lower peak intensity and therefore can operate at higher repetition rates, driven by a robust ${\sim}{{10}}\;{\rm{W}}$ fiber-laser system in a compact setup. Additionally, we present numerical simulations that explore the fundamental capabilities and spatiotemporal dynamics of highly cascaded harmonic generation. This VUV source can enhance the capabilities of spectroscopies of molecular and quantum materials, such as photoionization mass spectrometry and time-, angle-, and spin-resolved photoemission.

中文翻译：

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在负曲率空心光纤中通过高度级联谐波产生的超快1 MHz真空紫外光源

真空紫外（VUV）光对于研究分子和材料至关重要，但是事实证明，以高重复频率在VUV区域产生飞秒脉冲非常困难。在这里，我们展示了在负曲率空心光纤中使用高度级联的四波混合过程以兆赫兹重复频率有效生成VUV光的过程。偶数和奇数次谐波都可生成至15次谐波（69 nm，18.0 eV），具有高能量分辨率$ {\ sim} {{40}} \; {\ rm {meV}} $。与直接高次谐波生成相反，这种高度级联的谐波生成过程需要较低的峰值强度，因此可以在强大的$ {\ sim} {{10}} \; {\ rm {W}}的驱动下以较高的重复频率运行。$紧凑型设置中的光纤激光系统。此外，我们提供了数值模拟，以探索高度级联谐波生成的基本功能和时空动力学。这种VUV光源可以增强分子和量子材料的光谱学功能，例如光电离质谱，时间，角度和自旋分辨光发射。