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arXiv:0912.0747 · Physical Review A

Method for deducing anisotropic spin-exchange rates

Thad G Walker, Ian A. Nelson, Stephen J. Kadlecek

Published Mar 29, 2010• 8 citations
arXivHTMLPDF

Abstract

Using measured spin-transfer rates from alkali-metal atoms to $^{3}\mathrm{He}$, combined with spin-relaxation rates of the alkali-metal atoms due to $^{3}\mathrm{He}$ and $^{4}\mathrm{He}$, it should be possible to differentiate between isotropic and anisotropic spin exchange. This would give a fundamental limit on the $^{3}\mathrm{He}$ polarization attainable in spin-exchange optical pumping. For K-He, we find the limit to be $0.90\ifmmode\pm\else\textpm\fi{}0.11$.

DOI
10.1103/physreva.81.032709

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By measuring the relaxation rates of the nuclear spin polarization of 129Xe^{129}\mathrm{Xe}129Xe in the presence of alkali-metal vapor at different densities, we have extracted the spin-exchange rates between 129Xe^{129}\mathrm{Xe}129Xe and the three alkali metals K, Rb, and Cs. By studying the alkali-metal--129Xe^{129}\mathrm{Xe}129Xe spin-exchange rates as functions of the cell number density from 0.2 to 0.7 amagat, the binary collision and van der Waals molecular terms are separated, and constants governing both mechanisms are determined. The results from our work can be used to optimize the parameter space for polarizing 129Xe^{129}\mathrm{Xe}129Xe, a promising agent for magnetic resonance imaging and other applications.
The standard model of Spin-Exchange Optical Pumping of 3 He has come under close scrutiny as researchers try to maximize the quantity and polarization of 3 He. This paper will review four important effects that have come to light: 1) pumping with frequency narrowed diode lasers significantly improves the polarization and production rate as compared to off-the-shelf broadband sources 2) Rb-K mixtures again improve the production rate due to reduced collisional loss in K-He collisions, 3) a unexplained 3 He wall relaxation mechanism that scales closely with alkali vapor pressure limits the attainable 3 He polarization to about 80%, 4) a small collisionally-induced breakdown in the selection rules for optical pumping explains why narrowband lasers are so advantageous, and may explain some observed limitations for Rb-K pumping as well.