Transition Frequencies and Hyperfine Structure in ${}^{113,115}$In${}^{+}$: Application of a Liquid-Metal Ion Source for Collinear Laser Spectroscopy

Abstract

We demonstrate the first application of a liquid-metal ion source for collinear laser spectroscopy in proof-of-principle measurements on naturally abundant In${}^{+}$. The superior beam quality, i.e., the actively stabilized current and energy of a beam with very low transverse emittance, allowed us to perform precision spectroscopy on the $5s^2{}^1{\mathrm{S}}_0\to 5s5p{}^3{\mathrm{P}}_1$ intercombination transition in ${}^{115}$In${}^{+}$, which is to our knowledge the slowest transition measured with collinear fluorescence laser spectroscopy so far. By applying collinear and anticollinear spectroscopy, we improved the center-of-gravity frequency $\hat{I}{½}_{\mathrm{cg}}=1299617759.3(1.2)$ and the hyperfine constants $A=6957.19(28)$\,MHz and $B=-443.7(2.4)$\,MHz by more than two orders of magnitude. A similar accuracy was reached for ${}^{113}$In${}^{+}$ in combination with literature data and the isotope shift between both naturally abundant isotopes was deduced to $\hat{I}½{(}^{113}\mathrm{In})-\hat{I}½{(}^{115}\mathrm{In})=696.3(3.1)$\,MHz. Nuclear alignment induced by optical pumping in a preparation section of the ion beamline was demonstrated as a pump-and-probe approach to provide sharp features on top of the Doppler broadened resonance profile.