Gyromagnetic Ratio of Helium2S13Atoms By Optical Pumping: Level Shifts

Abstract

The gyromagnetic ratio of optically aligned $2^{3}S_{1}$ helium atoms has been measured by comparing its Zeeman resonance frequency with the proton transition frequency in the earth's magnetic field. The value of $\frac{{\ensuremath{\gamma}}_{\mathrm{He}}}{2\ensuremath{\pi}}$ extrapolated to zero light intensity is (2.80235 \ifmmode\pm\else\textpm\fi{} 0.000 03) \ifmmode\times\else\texttimes\fi{}${10}^{6}$ Hz ${\mathrm{G}}^{\ensuremath{-}1}$. The use of unpolarized light to align the helium sample reduces the $g$ factor by an amount proportional to the pumping light intensity. This displacement results from an admixture of the excited-state ($2^{3}P_{2}$) $g$ factor into the $2^{3}S_{1}$ state during the optical pumping cycle. When the pumping light is circularly polarized, an additional shift appears, caused by virtual transitions related to the dispersion of the pumping light.