Spin-Exchange Optical Pumping of Alkali Salts

Spin-Exchange Optical Pumping (SEOP) is a technique used to polarize nuclei in excess of their equilibrium limit. SEOP is achieved by optically pumping an alkali vapor which then transfers angular momentum to the nuclei of interest. We have recently hyperpolarized $^{133}$Cs nuclei in solid CsH using SEOP, achieving magnetizations more than an order of magnitude larger than the thermal equilibrium value.\footnote{Ishikawa \emph{et. al.}, Phys. Rev. Lett. {\bf 98}, 183004 (2007)} In subsequent work, we investigate the mechanisms underlying this transfer of angular momentum. By optically pumping Cs vapor with laser light resonant with several optical transitions, each yielding different nuclear and electronic spin currents to the solid, we attempt to determine the source of transferred angular momentum. Early evidence suggests both electronic and nuclear spin polarization in the vapor contribute to $^{133}$Cs nuclear polarization in the salt. The $^1$H polarization is also mildly affected by optical pumping. We compare these results to numerical simulations and to results from other alkali salts. Further studies are warranted to discover if polarization can be transferred to other nuclei (e.g., alkali salts) on the cell walls.