Investigating Rubidium Density and Temperature Distributions in a High-Throughput (129)Xe-Rb Spin-Exchange Optical Pumping Polarizer

Accurate knowledge of the rubidium (Rb) vapor density, [Formula: see text] , is necessary to correctly model the spin dynamics of [Formula: see text] Xe-Rb spin-exchange optical pumping (SEOP). Here we present a systematic evaluation of [Formula: see text] within a high-throughput [Formula: see text] Xe-Rb hyperpolarizer during continuous-flow SEOP. Near-infrared ([Formula: see text] (D [Formula: see text])/5 [Formula: see text] (D [Formula: see text])) and violet ([Formula: see text] /6 [Formula: see text]) atomic absorption spectroscopy was used to measure [Formula: see text] within 3.5 L cylindrical SEOP cells containing different spatial distributions and amounts of Rb metal. We were able to quantify deviation from the Beer-Lambert law at high optical depth for D [Formula: see text] and 6 [Formula: see text] absorption by comparison with measurements of the D [Formula: see text] and 6 [Formula: see text] absorption lines, respectively. D [Formula: see text] absorption deviates from the Beer-Lambert law at [Formula: see text] m [Formula: see text] whilst 5 [Formula: see text] S [Formula: see text] absorption deviates from the Beer-Lambert law at [Formula: see text] m [Formula: see text]. The measured [Formula: see text] was used to estimate a [Formula: see text] Xe-Rb spin exchange cross section of [Formula: see text] m [Formula: see text] s [Formula: see text] , consistent with spin-exchange cross sections from the literature. Significant [Formula: see text] heterogeneity was observed in a SEOP cell containing 1 g of Rb localized at the back of the cell. While [Formula: see text] homogeneity was improved for a greater surface area of the Rb source distribution in the cell, or by using a Rb presaturator, the measured [Formula: see text] was consistently lower than that predicted by saturation Rb vapor density curves. Efforts to optimize [Formula: see text] and thermal management within spin polarizer systems are necessary to maximize potential future enhancements of this technology.