High Efficiency Hyperfine Pumping of Cesium Vapor

The hyperfine pumping of cesium vapor has been obtained by using a magnetic filter for the pumping light. The filter transmits the hyperfine component of the $D_1$ resonance line which starts from the $F=4\mathrm{}$ sublevel of the ground state. The level which is populated with the hyperfine pumping is therefore that with $F=3\mathrm{}$. Neon has been used as a buffer gas, and the best results were obtained for a pressure of 20 Torr. In this condition, 15% of the Cs atoms in the hyperfine level $F=4\mathrm{}$ are transferred into the $F=3\mathrm{}$ level. The relaxation time, as a function of Cs vapor density, has been measured for five values of the neon pressure, and the Cs-Cs spin-exchange cross section has been determined to be (2.20±0.15) × ${10}^{-14\mathrm{}}$ ${\mathrm{cm}}^2$.