Nuclear polarization of 3He gas at and below 4.2 K by room temperature laser optical pumping

Ground state nuclear polarizations up to 50% have been produced in 3He gas at liquid helium temperatures and number densities of order 1018 cm-3 by a polarization transfer technique. 3He gas in a room temperature pyrex cell is optically pumped by light from a color center laser. Polarized ground state atoms diffuse to a second cell immersed in a liquid helium bath. That part of the double cell interior surface near liquid helium temperatures is coated with frozen molecular hydrogen. Under good conditions over 90% of the polarization in the pumping cell is transferred to the cold cell