Doppler-free resonantly enhanced two-photon spectroscopy ofnpandnfRydberg states in atomic cesium

Abstract

The fine-structure intervals of selected $\mathrm{np} (n=18\ensuremath{-}83)$ and $\mathrm{nf} (n=14\ensuremath{-}28)$ Rydberg states in neutral Cs have been measured by Doppler-free resonantly enhanced two-photon laser spectroscopy with a thermionic diode detector. One cw dye laser was tuned near resonance with a $6s\ensuremath{-}5d$ electric quadrupole transition while a second was scanned through the relevant $5d\ensuremath{-}np$, $\mathrm{nf}$ transitions. This is the first Doppler-free study of these series by strictly optical methods. The experimental fine-structure intervals are in good agreement with splitting formulas derived by other authors from fine-structure measurements of lower-lying $\mathrm{np}$ and $\mathrm{nf}$ levels. Our results and the best previous data have been fitted with several expressions that have been used or suggested for the representation of fine-structure data. A recently proposed expansion formula including inverse even powers of the effective quantum number is found to have little practical significance for the description of experimental intervals.