Analysis of nonresonant effects in the two-photon spectroscopy of helium

TL;DR

This paper investigates nonresonant quantum interference effects in helium two-photon spectroscopy, revealing significant line profile asymmetries that impact the accuracy of transition frequency measurements and highlight the need for refined experimental corrections.

Contribution

It identifies and quantifies nonresonant interference effects in helium spectroscopy, emphasizing their importance for precise frequency measurements and future experimental designs.

Findings

Line profile asymmetry can reach tenths of a megahertz.

Nonresonant corrections are essential for accurate helium transition measurements.

Current discrepancies between theory and experiment are not fully resolved.

Abstract

In the present paper, we study nonresonant corrections for experimental measurements of the transition frequencies in the helium atom. Having attracted more attention, such effects can make a significant contribution to experiments based on one- and two-photon atomic spectroscopy. The quantum interference effects in the measurements of $2^3S_1-n^3D_1$ ($ n=3,\,4,\,5 $) transition frequencies based on Doppler-free two-photon spectroscopy, are considered as a possible source of current discrepancy between the experimental and theoretical data. We demonstrate that line profile asymmetry caused by the quantum interference of fine sub-levels of the $ ^3D_{J} $ $ (J=1,2,3) $ state can reach tenths of a megahertz for different experimental conditions. Thus, previously unaccounted nonresonant corrections should be taken in next-generation experimental measurements of transitions frequencies in helium. However, they could not completely eliminate the current imbalance in the study of helium spectra and the question is still open.