Spin relaxation of optically pumped cesium in high magnetic fields

Cs vapor in He, Ne, and Ar buffer gases has been optically pumped in magnetic fields as high as 100 kG. The rate of electronic spin relaxation measured in Cs-Ar is approximately the same as that predicted by the low-field nuclear-spin-independent cross section for the relaxation of $〈S_z〉$ via the $\gamma \left(\overrightarrow{\mathrm{S}}·\overrightarrow{\mathrm{N}}\right)$ (spin-orbit) interaction. In the cases of Cs-He and Cs-Ne, considerably higher relaxation rates are measured at high fields than those that are predicted from the low-field cross sections. The differences are shown to be due to relaxation arising from the collision-induced modification of the Cs hyperfine interaction, $\delta a\left(\overrightarrow{\mathrm{S}}·\overrightarrow{\mathrm{I}}\right)$. Upper limits of the order of ${10}^{-13\mathrm{}}$ sec are set for the average durations of both the $\delta a\left(\overrightarrow{\mathrm{S}}·\overrightarrow{\mathrm{I}}\right)$ and the $\gamma \left(\overrightarrow{\mathrm{S}}·\overrightarrow{\mathrm{N}}\right)$ interactions in sudden binary collisions of Cs atoms with light noble-gas atoms. The average cross sections for the $\delta a\left(\overrightarrow{\mathrm{S}}·\overrightarrow{\mathrm{I}}\right)$ interactions are estimated to be 1.3 × ${10}^{-14\mathrm{}}$ ${\mathrm{cm}}^2$ for Cs-He, and 0.73 × ${10}^{-14\mathrm{}}$ ${\mathrm{cm}}^2$ for Cs-Ne.