100  MHz frequency comb for low-intensity multi-photon studies: intra-cavity velocity-map imaging of xenon

Abstract

We raise the power from a commercial 10 W frequency comb inside an enhancement cavity and perform multi-photon ionization of gas-phase atoms at 100 MHz for the first time, to the best of our knowledge. An intra-cavity velocity-map-imaging setup collects electron-energy spectra of xenon at rates several orders of magnitude higher than those of conventional laser systems. Consequently, we can use much lower intensities ∼ 10 12 W / c m 2 without increasing acquisition times above just a few seconds. The high rate and coherence of the stabilized femtosecond pulses are known to be transferred to the actively stabilized cavity and will allow studying purely perturbative multi-photon effects, paving the road towards a new field of precision tests in nonlinear physics.

An ultralow-noise superconducting radio-frequency ion trap for frequency metrology with highly charged ions

“…Using the recently established techniques for trapping, 63 cooling, 37,63 and subsequent interrogation of HCI by QLS, 37 this new apparatus, in combination with the XUV frequency comb, [48][49][50] promises the implementation of XUV frequency metrology based on HCI.…”

“…Since we aim for direct frequency comb spectroscopy of HCI in the extreme ultraviolet (XUV) range, a dedicated XUV frequency comb based on highharmonic-generation inside an optical enhancement cavity has been set up and commissioned at MPIK. [48][49][50]…”

XUV frequency comb operation in an astigmatism-compensated enhancement cavity

“…Realizing this XUV comb is an important step towards performing the first ultra-high precision spectroscopy on HCI in this spectral region. Furthermore, the novel cavity enables multi-photon ionization experiments at a much lower intensity and higher precision than hitherto possible [54]. Moreover, the XUV comb could be employed to search for the nuclear transition in the 229m Th isomer, since the 7th harmonic of our comb matches with its most accurately determined energy…”

Interrogating the Temporal Coherence of EUV Frequency Combs with Highly Charged Ions

“…Highly charged ions (HCIs) can be produced, e.g., in an electron-beam ion trap (EBIT) [23] and then be moved to a cryogenic Paul trap [24][25][26] for interactions with external lasers [26][27][28]. Due to the existence of environmentinsensitive forbidden optical transitions, HCIs are of great interest in frequency metrology and for tests of fundamental physics [29,30] such as testing the hypothesis of fine-structure-constant variation [31][32][33][34] and for constraining the strength of a possible fifth force acting between electrons and nucleons [35,36].…”