A closed-form expression for spin-exchange rate correctly predicts experimental Xe polarization values under SEOP

Since its advent, the original spin-exchange optical pumping (SEOP) theory developed by Happer et al. has been adapted to predict experimental Xe polarization values. However, these adaptations have been poor predictors of Xe polarization values, leading to a search for additional depolarization mechanisms. Here, we revisit the general theory of spin-exchange optical pumping to understand the origin of such discrepancy and perform experimental measurements to validate our theoretical findings. The original theory of SEOP was used to derive a general closed-form expression for the spin-exchange between any alkali metal and noble gas atom. We then used this expression, which is different from that used in more recent theoretical models, along with previously measured constants to estimate the Rb-Xe spin-exchange cross section under different experimental conditions. We found good agreement between our theoretical cross section and the experimental cross section measured using a combination of optical absorption spectroscopy, field cycling, and NMR spectroscopy. By using the correct expression for the spin-exchange cross section, theoretical Xe polarization values that closely match those obtained experimentally are predicted for our system and for those found in the literature.