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Abstract:
Pushing precision spectroscopy towards shorter wavelengths not only reduces the quantum projection noise but also facilitates spectroscopy of highly charged ions or the thorium isomer 229mTh, which are promising candidates for the search for new physics beyond the Standard Model. In pursuit of this objective, we present the first-ever velocity-map imaging (VMI) measurement using an extreme ultraviolet (XUV) frequency comb, measuring the angular momentum distribution of photoelectrons originating from the direct photoionization of neutral xenon. To that end, the reliability of the XUV frequency comb is improved to enable long-term operation, as demonstrated with a measurement run over five days, capable of producing harmonics with an energy of up to 42,eV. Furthermore, a dedicated VMI spectrometer is designed, numerically evaluated, and implemented into the existing XUV frequency comb beamline. An embedded Sikler lens is tested for novel operation modes to further improve the energy resolution or manipulate the photoelectron imaging process. Additionally, the experimental setup is conceptualized for a future cold atomic beam, which will facilitate the first spectroscopic measurements with our XUV frequency comb. For this purpose, we identify Rydberg states in argon and calculate their lifetimes numerically. The predicted energy resolution of 0.4% enables the VMI spectrometer to experimentally separate photoelectrons originating from neighboring states.
