Collisional electron paramagnetic resonance frequency shifts in Cs-Rb-Xe mixtures

We report a measurement of the ratio of dimensionless enhancement factors κ0 for Cs-Xe129 and Rb-Xe129 in the temperature range 115-140 â C; both pairs are used in spin-exchange optical pumping (SEOP) to produce hyperpolarized Xe129. κ0 characterizes the amplification of the Xe129 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 electron paramagnetic resonance (EPR) frequency shifts caused by the SEOP polarization and subsequent sudden destruction of the same quantity of Xe129 magnetization were made for Cs133 and either Rb87 or Rb85. 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 (κ0)CsXe/(κ0)RbXe=1.215±0.007 with no apparent temperature dependence. Based on our previous measurement (κ0)RbXe=518±8, we determine (κ0)CsXe=629±10, which is more precise than, but consistent with, a previous measurement made by J. Fang et al. [Chin. Phys. B 23, 063401 (2014)10.1088/1674-1056/23/6/063401].