Polarization of the nuclear spins of noble-gas atoms by spin exchange with optically pumped alkali-metal atoms

The theory of spin exchange between optically pumped alkali-metal atoms and noble-gas nuclei is presented. Spin exchange with heavy noble gases is dominated by interactions in long-lived van der Waals molecules. The main spin interactions are assumed to be the spin-rotation interactions γ→N·→S between the rotational angular momentum →N of the alkali-metal---noble-gas pair and the electron spin →S of the alkali-metal atom, and the contact hyperfine interaction α→K·→S between the nuclear spin →K of the noble-gas atom and the electron spin →S. Arbitrary values for K and for the nuclear spin I of the alkali-metal atom are assumed. Precise formal expressions for spin transfer coefficients are given along with convenient approximations based on a perturbation expansion in powers of (αγN)², a quantity which has been shown to be small by experiment.