Spin-Exchange Cross Section forRb85-Rb87Collisions

The spin-exchange cross section for ${\mathrm{Rb}}^{85}$-${\mathrm{Rb}}^{87}$ collisions has been measured to be (1.70±0.21)×${10}^{-14\mathrm{}}$ ${\mathrm{cm}}^2$ using the techniques of optical pumping and an interferometric method for measuring the Rb vapor density. The ${\mathrm{Rb}}^{87}$ constituent in a vapor of natural Rb was polarized through absorption of circularly polarized resonance radiation, and the ${\mathrm{Rb}}^{87}$ polarization was partially transferred to the ${\mathrm{Rb}}^{85}$ constituent through spin-exchange collisions. A phenomenological theory of the optical pumping plus the exchange polarization process which neglects nuclear spin was used to relate the cross section to the ratio of the signal strengths for the ${\mathrm{Rb}}^{87}$ and ${\mathrm{Rb}}^{85}$ Zeeman resonances, the relaxation time, and the ${\mathrm{Rb}}^{87}$ vapor density. The density was measured by comparing spectral profiles of the resonance radiation transmitted through the optical pumping cell at room temperature with the resonance radiation transmitted at the temperature at which the signal strengths were measured. These spectral profiles were obtained through use of a scanning Fabry-Perot interferometer.