We demonstrate spin-exchange optical pumping of ${}^3\mathrm{H}\mathrm{e}$ using a “hybrid” K-Rb vapor mixture. The Rb atoms absorb light from a standard laser at 795 nm, then collisionally polarize the potassium atoms. Spin-exchange collisions of K and ${}^3\mathrm{H}\mathrm{e}$ atoms then transfer the angular momentum to the ${}^3\mathrm{H}\mathrm{e}$ with much greater efficiency than $\mathrm{R}\mathrm{b}\mathrm{\text{−}}{}^3\mathrm{H}\mathrm{e}$. For a K-rich vapor, the efficiency of the hybrid spin-exchange collisions approaches $1/4$, an order of magnitude greater than achieved by pure Rb pumping. We present the first measurements of actual photon efficiencies (polarized nuclei produced per absorbed photon), and show that a new parasitic absorption process limits the total efficiencies for both hybrid and pure Rb pumping.

• Received 16 May 2003

DOI:https://doi.org/10.1103/PhysRevLett.91.123003