Spin-Exchange Optical Pumping of Solid Alkali Compounds*

We demonstrate enhancement of the $^{133}$Cs nuclear polarization in a film of cesium hydride which has been placed in contact with an optically pumped cesium vapor. The maximum observed polarization at 9.4 T and 137 $^{\circ}$C is roughly 4 times the equilibrium polarization, but higher magnetizations are possible at lower magnetic fields. In an attempt to determine the mechanism of spin transfer from the alkali vapor to the solid, we have performed this experiment at intermediate magnetic fields (1-2 tesla) while pumping different optical transitions in the vapor. We will discuss the predicted spin current to the CsH layer in this regime of partial hyperfine decoupling and propose new methods for generating even higher polarizations in the solid. Potential applications of this technique will be mentioned as well as its extension to other compounds.