Polarization-Dependent Disappearance of a Resonance Signal -- Indication for Optical Pumping in a Storage Ring?

TL;DR

This study demonstrates that circularly polarized laser light causes optical pumping in Li$^+$ ions within a storage ring, leading to the disappearance of resonance signals and enabling the creation of polarized ion beams for advanced experiments.

Contribution

The paper provides the first detailed experimental and theoretical analysis of polarization-dependent resonance disappearance due to optical pumping in a storage ring setting.

Findings

Circularly polarized light causes resonance signal disappearance.

Optical pumping leads to polarization of ions in the storage ring.

Polarized ion beams can be used for new parity violation experiments.

Abstract

We report on laser spectroscopic measurements on Li$^+$ ions in the experimental storage ring ESR at the GSI Helmholtz Centre for Heavy Ion Research. Driving the $2s\,^3\!{S}_1\;(F=\frac{3}{2}) \,\leftrightarrow\,2p\,^3\!P_2\;(F=\frac{5}{2}) \leftrightarrow 2s\,^3\!{S}_1\;(F=\frac{5}{2})$ $\Lambda$-transition in $^7$Li$^+$ with two superimposed laser beams it was found that the use of circularly polarized light leads to a disappearance of the resonance structure in the fluorescence signal. This can be explained by optical pumping into a dark state of polarized ions. We present a detailed theoretical analysis of this process that supports the interpretation of optical pumping and demonstrates that the polarization induced by the laser light must then be at least partially maintained during the round trip of the ions in the storage ring. Such polarized ion beams in storage rings will provide opportunities for new experiments, especially on parity violation.