Motional-Stark-effect spectroscopy:7S1−9P1energy separation and Zeeman tuning parameters forHe4

Abstract

The $7{}_{}{}^1{}_{}{}^{}S-9\mathrm{}{}_{}{}^1{}_{}{}^{}P$ energy separation of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ has been measured by the method of laser magnetic resonance in electron-beam-excited ${}_{}{}^4{}_{}{}^{}\mathrm{He}$. The measurements have also provided Zeeman tuning coefficients for terms up to fourth order in the field $B$. Motional-Stark-effect (MSE)-dominated line shapes are observed at most fields. These line shapes are analyzed, and their Doppler-free portions used to obtain a value for the energy separation with a precision exceeding 1 ppm ($\Delta E_o=980.7979\mathrm{}\pm 0.0002$ ${\mathrm{cm}}^{-1\mathrm{}}$). Arguments are presented that show the importance of the MSE in magnetically confined hot plasmas and in certain collapsed stars possessing high magnetic fields.