Collisional EPR Frequency Shifts in Cs-Rb-Xe Mixtures

TL;DR

This study precisely measures the ratio of enhancement factors for Cs-Xe and Rb-Xe mixtures in spin-exchange optical pumping, improving accuracy and consistency with previous findings.

Contribution

It provides a more precise measurement of the ratio of enhancement factors for Cs-Xe and Rb-Xe, addressing systematic errors and confirming previous results.

Findings

Measured $()_{CsXe}/()_{RbXe} = 1.215 b0 0.007

Determined $()_{CsXe} = 629 b0 10

No temperature dependence observed in the ratio

Abstract

We report a measurement of the ratio of dimensionless enhancement factors $\kappa_0$ for Cs-$^{129}$Xe and Rb-$^{129}$Xe in the temperature range $115-140\, ^{\circ}$C; both pairs are 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 alkali-metal electronic effective field, compared to the case of a uniform continuous medium in classical magnetostatics. The measurement was carried out in "hybrid" vapor cells containing both Rb and Cs metal in a prescribed ratio, producing approximately the same vapor density for both. Alternating measurements of the optically detected EPR frequency shifts caused by the SEOP polarization and subsequent sudden destruction of the same quantity of $^{129}$Xe magnetization were made for $^{133}$Cs and either $^{87}$Rb or $^{85}$Rb. An important source of systematic error caused by power fluctuations in the pump laser that produced variable light shifts in the EPR frequency was characterized and then mitigated by allowing sufficient warm-up time for the pump laser. We measured $(\kappa_0)_{\rm CsXe}/(\kappa_0)_{\rm RbXe} = 1.215 \pm 0.007$ with no apparent temperature dependence. Based on our previous measurement $(\kappa_0)_{\rm RbXe}=518 \pm 8$, we determine $(\kappa_0)_{\rm CsXe} = 629 \pm 10$, more precise than but consistent with a previous measurement made by another research group.