Mainz 2026 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 14: Precision Spectroscopy of Atoms and Ions I (joint session A/Q)

Q 14.6: Talk

Monday, March 2, 2026, 18:30–18:45, N 3

Towards the first 1S-2S Measurement in Atomic Tritium — •Hendrik Schürg and Randolf Pohl — Johannes Gutenberg-Universität Mainz, Institut für Physik, QUANTUM & Exzellenzcluster PRISMA⁺, Mainz, Germany

Laser spectroscopy is an effective method for obtaining high-precision results for the root-mean-square charge radii of nuclei. Here, we outline a route towards the first measurement of the 1S-2S interval in atomic tritium – giving access to the triton charge radius through the hydrogen-tritium 1S-2S isotope shift. Our approach relies on a compact radio-frequency discharge cell that will safely confine the radioactive tritium gas and enables optogalvanic detection of the resonant excitation to the 2S state via the laser-induced perturbation of the plasma’s impedance. So far, we have demonstrated Doppler-free intermodulated optogalvanic spectroscopy of the hydrogen Balmer-β fine structure components near 486 nm. For the two-photon 1S-2S transition at 243 nm, we analyze expected line shifts and broadenings, and estimate an optogalvanic signal strength based on a collisional-radiative plasma model. Achieving the required laser intensity will involve the integration of the discharge cell into a deep-uv enhancement cavity.

Keywords: hydrogen; tritium; optogalvanic laser spectroscopy; 1S-2S isotope shift; nuclear charge radii