Nauta J, Oelmann J-H, Borodin A, Ackermann A, Knauer P, Muhammad I S, Pappenberger R, Pfeifer T, Crespo López-Urrutia J R
Opt Express. 2021 Jan 18;29(2):2624-2636. doi: 10.1364/OE.414987.
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 w = 15 µm waist cavity focus. With a gas jet installed there, intensities reaching ∼ 10 W/cm 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.
我们已开发出一种极紫外（XUV）频率梳，用于对高电荷离子（HCI）中发现的众多XUV跃迁进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，然后被馈入超高真空腔内的飞秒增强腔（fsEC）。低色散fsEC将数百个入射脉冲相干叠加，并通过单个柱面光学元件，在w = 15 µm腰腔焦点处完全补偿像散。在那里安装气体喷射装置后，强度达到~ 10 W/cm会产生频率为100 MHz梳状光谱的相干高次谐波。我们从fsEC中耦合出从第7次到第35次（42 eV；30 nm）的谐波，用于即将开展的HCI频率计量实验。
