Laser Excitation of the 1S-2S Transition in Singly-Ionized Helium

TL;DR

This paper demonstrates laser excitation of the 1S-2S transition in singly-ionized helium using a frequency comb and harmonic generation, enabling high-precision spectroscopy for fundamental physics tests.

Contribution

It presents the first laser excitation of the 1S-2S transition in singly-ionized helium using a novel comb-based approach.

Findings

Resonance observed with ~10^-4 excitation probability per pulse

Results match simulations accurately

Paves the way for high-precision helium ion spectroscopy

Abstract

Precision laser spectroscopy in the extreme ultraviolet of the 1S-2S two-photon transition in singly-ionized helium is a promising route for tests of fundamental physics. We demonstrate laser excitation of this transition in an atomic beam of $^3$He, based on an amplified frequency comb pulse at 790 nm combined with its 25$^{\text{th}}$ harmonic at 32 nm. A clear resonance is observed with a maximum excitation probability of close to 10$^{-4}$ per pulse, and the results are well described by our simulations. This paves the way for high-precision Ramsey-comb spectroscopy of a single helium ion in a Paul trap.