XUV frequency comb production with an astigmatism-compensated enhancement cavity

Abstract

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.

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]…”

New Horizons: Scalar and Vector Ultralight Dark Matter

“…It has a frequency of 4.96 × 10 16 Hz, a linewidth of only 5 × 10 −8 Hz, and the highest quality factor hitherto found in an excited atomic system. Such HCI species will be used in combination with extreme-ultraviolet frequency combs [382][383][384][385] for laser stabilization and frequency metrology using schemes that have been theoretically analysed for their feasibility [386], and could offer much higher sensitivities to hypothetical particles and fields.…”

An atom interferometer driven by a picosecond frequency comb

“…Although we implemented it in the visible spectrum around 800 nm to drive Raman transitions in rubidium atoms, this technique holds great promises for extending atom interferometry to other spectral regions (deep-UV, V-UV, X-UV). Indeed, one can benefit from the high peak intensity of the ultrashort pulses which makes frequency conversion in crystals and gas targets more efficient, as shown by the remarkable progress in the generation of XUV frequency combs for high precision spectroscopy [6,[22][23][24]. Therefore, frequency-comb-driven atom interferometry could eventually open the door for extending interferometry to new transitions and new species for novel possibilities in metrology, sensing of gravito-inertial effects and tests of fundamental physics.…”