Here, we report on a novel narrowband High Harmonic Generation (HHG) light source designed for ultrafast photoelectron spectroscopy (PES) on solids. Notably, at 16.9 eV photon energy, the harmonics bandwidth equals 19 meV. This result has been obtained by seeding the HHG process with 230 fs pulses at 515 nm. The ultimate energy resolution achieved on a polycrystalline Au sample at 40 K is ∼22 meV at 16.9 eV. These parameters set a new benchmark for narrowband HHG sources and have been obtained by varying the repetition rate up to 200 kHz and, consequently, mitigating the space charge, operating with ≈ 3 × 10 7 electrons/s and ≈ 5 × 10 8 photons/s. By comparing the harmonics bandwidth and the ultimate energy resolution with a pulse duration of ∼105 fs (as retrieved from time-resolved experiments on bismuth selenide), we demonstrate a new route for ultrafast space-charge-free PES experiments on solids close to transform-limit conditions.

中文翻译：

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用于17-31 eV光子能量范围内的超快光电子光谱学的相干窄带光源。

在这里，我们报道了一种新颖的窄带高谐波产生（HHG）光源，该光源设计用于固体上的超快速光电子能谱（PES）。值得注意的是，在16.9 eV的光子能量下，谐波带宽等于19 meV。通过在515 nm处注入230 fs脉冲的HHG工艺来获得此结果。在16.9 eV时，多晶Au样品在40 K时达到的最终能量分辨率约为22 meV。这些参数为窄带HHG光源树立了新的基准，并已通过在高达200 kHz的频率下改变重复频率来获得，从而减轻了空间电荷，并以≈3×10 7电子/ s和≈5×10 8光子/ s。通过比较谐波带宽和脉冲持续时间约为105 fs的最终能量分辨率（从硒化铋的时间分辨实验中得出），