Physical Review Letters
Optical Detection of Nonradiating Alkali Atoms in Solid Helium
T. Eichler, R. Müller-Siebert, Daniel Nettels, S. I. Kanorsky, Antoine Weis
Abstract
We have detected by optical means nonfluorescing ${}^{85}\mathrm{Rb}$ and ${}^{87}\mathrm{Rb}$ atoms implanted in a body centered cubic ${}^{4}\mathrm{He}$ crystal. In contrast to cesium the resonance fluorescence of rubidium is strongly quenched by the helium matrix, and the weak resonance absorption of the two Rb isotopes was detected using a double resonance technique. From a comparative study of the (optically detected) magnetic resonance spectra of ${}^{85}\mathrm{Rb}$, ${}^{87}\mathrm{Rb}$, and ${}^{133}\mathrm{Cs}$ we infer their effective ${g}_{F}$ factors and conclude that they are not perturbed by the He matrix at a level of $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$. We show further that optical pumping of Rb proceeds via depopulation, whereas for Cs it proceeds via repopulation.