1S-3S cw spectroscopy of hydrogen/deuterium atom

TL;DR

This paper reports precise measurements of the 1S-3S transition in hydrogen using continuous-wave laser spectroscopy, contributing to fundamental physics tests and exploring systematic effects in deuterium.

Contribution

It presents a high-precision measurement of the hydrogen 1S-3S transition frequency and discusses improvements and challenges in extending the measurement to deuterium.

Findings

Achieved a relative uncertainty of 9×10⁻¹³ in hydrogen transition frequency

Observed broadened fluorescence signals in deuterium due to atom accumulation

Discussed potential systematic effects affecting the measurements

Abstract

We study the 1S-3S two-photon transition of hydrogen in a thermal atomic beam, using a homemade cw laser source at 205 nm. The experimental method is described, leading in 2017 to the measurement of the 1S-3S transition frequency in hydrogen atom with a relative uncertainty of $9 \times 10^{-13}$. This result contributes to the "proton puzzle" resolution but is in disagreement with the ones of some others experiments. We have recently improved our setup with the aim of carrying out the same measurement in deuterium. With the improved detection system, we have observed a broadened fluorescence signal, superimposed on the narrow signal studied so far, and due to the stray accumulation of atoms in the vacuum chamber. The possible resulting systematic effect is discussed.