Interrogating the temporal coherence of EUV frequency combs with highly charged ions

TL;DR

This paper proposes a method to verify the temporal coherence of EUV frequency combs using highly charged ions, enabling ultra-precise spectroscopy and coherence measurement over unprecedented time scales.

Contribution

It introduces a novel scheme to assess EUV comb coherence via excitation dynamics of highly charged ions, extending coherence verification to much longer time scales.

Findings

Coherence time can be inferred from excitation spectra.

Microscopic origin of excitation equivalence demonstrated.

Potential for high-precision EUV spectroscopy with $rac{ riangle ext{omega}}{ ext{omega}} ext{~}10^{-17}$.

Abstract

A scheme to infer the temporal coherence of EUV frequency combs generated from intra-cavity high-order harmonic generation is put forward. The excitation dynamics of highly charged Mg-like ions, interacting with EUV pulse trains featuring different carrier-envelope-phase fluctuations, are simulated. While demonstrating the microscopic origin of the macroscopic equivalence between excitations induced by pulse trains and continuous-wave lasers, we show that the coherence time of the pulse train can be determined from the spectrum of the excitations. The scheme will provide a verification of the comb temporal coherence at time scales several orders of magnitude longer than current state of the art, and at the same time will enable high-precision spectroscopy of EUV transitions with a relative accuracy up to $\delta\omega/\omega\sim10^{-17}$.