Microwave-Optical Determination of Rydberg-State Fine Structure: The71D−7FIntervals in He

Abstract

We have measured the ${\mathrm{He}}^4$ electrostatic fine-structure intervals $7^1{D}_2-7^1{F}_3$ and $7^1{D}_2-7^3{F}_3$ neat 31.5 GHz. The latter transition appears because of spin-orbit mixing of singlet and triplet $7F$ states of the same $J$. The 3-ppm precision represents a ${10}^4$-fold improvement over the mean $7^{1}D-7F$ spectroscopic value. We have also measured the mean $7F-7G$ and $7G-7H$ intervals. The microwave-optical method used appears widely applicable to atomic and molecular Rydberg states.