High-precision determination of the frequency-shift enhancement factor in Rb-$^{129}$Xe

We report a measurement of the dimensionless enhancement factor $\kappa_0$ for the Rb-$^{129}$Xe pair commonly used in spin exchange optical pumping (SEOP) to produce hyperpolarized $^{129}$Xe. $\kappa_0$ characterizes the amplification of the $^{129}$Xe magnetization contribution to the Rb electronic effective field, compared to the case of a uniform continuous medium in classical magnetostatics. The measurement is carried out in Rb vapor cells containing both $^3$He and $^{129}$Xe and relies on the previously measured value of $\kappa_0$ for the Rb-$^3$He pair. The measurement is based on (1) the optically detected (Faraday rotation) frequency shift of the $^{87}$Rb EPR hyperfine spectrum caused by the SEOP nuclear polarization and subsequent sudden destruction of nuclear polarization of both species and (2) a comparison of NMR signals for the two species acquired just prior to the EPR frequency shift measurements. We find $(\kappa_0)_{\rm RbXe} = 518\pm 8$, in good agreement with previous measurements and theoretical estimates but with improved precision.