We have developed an extreme ultraviolet (XUV) frequency comb for performing ultra-high precision spectroscopy on the many XUV transitions found in highly charged ions (HCI). Femtosecond pulses from a 100 MHz phase-stabilized near-infrared frequency comb are amplified and then fed into a femtosecond enhancement cavity (fsEC) inside an ultra-high vacuum chamber. The low-dispersion fsEC coherently superposes several hundred incident pulses and, with a single cylindrical optical element, fully compensates astigmatism at the w₀ = 15 µm waist cavity focus. With a gas jet installed there, intensities reaching ∼ 10¹⁴ W/cm² generate coherent high harmonics with a comb spectrum at 100 MHz rate. We couple out of the fsEC harmonics from the 7th up to the 35th (42 eV; 30 nm) to be used in upcoming experiments on HCI frequency metrology.

中文翻译：

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具有像散补偿增强腔的XUV频率梳生产

我们已经开发了一种极紫外（XUV）频率梳，用于对高电荷离子（HCI）中发现的许多XUV跃迁执行超高精度光谱分析。来自100 MHz相位稳定的近红外频率梳的飞秒脉冲被放大，然后馈入超高真空室内的飞秒增强腔（fsEC）中。低分散FSEC相干地叠加几百事件脉冲，并与单一的圆柱形光学元件，在完全补偿散光瓦特₀ = 15 μ米腰部腔焦点。在安装气体喷射器的情况下，强度达到〜10 ¹⁴ W / cm ²产生具有100 MHz速率梳状频谱的相干高谐波。我们耦合了从7号到35号（42 eV; 30 nm）的fsEC谐波，以用于即将进行的HCI频率计量学实验。