Dynamic Nuclear Polarization of Liquid Helium-Three by Optical Pumping

Experiments are described wherein optical pumping of room-temperature ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ gas in diffusive contact with ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ liquid at 0.93°K yields dynamically enhanced nuclear spin polarization in the liquid. Steady-state polarization of 0.085% has been observed in a 20-${\mathrm{mm}}^3$ liquid sample, and transient polarization of 0.15% has been achieved in a 2-${\mathrm{mm}}^3$ sample. Using the same technique, 2% polarization was achieved in dense ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ gas at 4-mm Hg pressure and 0.93°K. The experiments were performed in an applied magnetic field of about 8 G, corresponding to a thermal equilibrium polarization of 7×${10}^{-5\mathrm{}}$%. An equation is derived to describe the diffusive transport of polarization from gas to liquid in the presence of polarization gradients, thermal gradients, and relaxation processes. The technique has the potential for producing polarized liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ nuclear scattering targets with polarizations approaching 10%.