Laser Excitation of the 1S-2S Transition in Singly-Ionized Helium
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 3He, based on an amplified frequency comb pulse at 790 nm combined with its 25th 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.
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