Study of Spin-Exchange Collisions in Vapors of ${\mathrm{Rb}}^{85}$, ${\mathrm{Rb}}^{87}$, and ${\mathrm{Cs}}^{133}$ by Paramagnetic Resonance

The effective spin-dephasing cross sections of ${\mathrm{Rb}}^{85}$, ${\mathrm{Rb}}^{87}$, and ${\mathrm{Cs}}^{133}$ caused by spin-exchange collisions have been measured using paramagnetic resonance techniques to examine the Zeeman transitions of these alkalis. The collision frequency was determined from the width of the absorption lines and the density of atoms by comparing the intensity of the signal with a CuS${\mathrm{O}}_4$·5${\mathrm{H}}_2$O crystal in the same cavity. The spin-dephasing cross sections of ${\mathrm{Rb}}^{85}$, ${\mathrm{Rb}}^{87}$, and ${\mathrm{Cs}}^{133}$ are 2.0, 1.9, and 2.3×${10}^{-14\mathrm{}}$ ${\mathrm{cm}}^2$. The 70% probable error is ±20%. The relation of these measured dephasing cross sections to the spin-exchange cross sections is discussed. The thermal relaxation times were measured also; it was found that they were best explained by the strong exchange coupling which enhanced a relatively weak relaxation mechanism.