Raman Transitions in Collinear Laser Spectroscopy for High-Precision Frequency Measurements

Abstract

We demonstrate stimulated Raman spectroscopy on dipole-forbidden fine-structure transitions in a fast ion beam. It is applied to the ${\mathrm{S}}_{1/2}\to {\mathrm{D}}_{5/2}$ clock transition in ${}^{88}{\mathrm{Sr}}^{+}$ and combined with a subsequent E1 transition to allow for its detection by standard fluorescence detection. Building on this, the ${\mathrm{D}}_{3/2}\to {\mathrm{D}}_{5/2}$ fine-structure splitting is measured directly using a Doppler-free scheme employing two subsequent Raman transitions. These measurements demonstrate a path toward precision collinear laser spectroscopy of narrow transitions on short-lived isotopes beyond the linewidth limit of conventional electric-dipole spectroscopy, which can be used to probe fundamental aspects of atomic and nuclear physics.