Metastability exchange optical pumping of 3He gas up to hundreds of millibars at 4.7 Tesla

Metastability exchange optical pumping (MEOP) is experimentally investigated in He-3 at 4.7 T, at room temperature and for gas pressures ranging from 1 to 267 mbar. The 2(3)S-2(3)P transition at 1083 nm is used for optical pumping and for detection of the laser-induced orientation of He-3 atoms in the rf discharge plasma. The collisional broadening rate is measured (12.0 +/- 0.4 MHz mbar(-1) FHWM) and taken into account for accurate absorption-based measurements of both nuclear polarization in the ground state and atom number density in the metastable 2(3)S state. The results lay the ground for a comprehensive assessment of the efficiency of MEOP, by comparison with achievements at lower field (1 mT-2 T) over an extended range of operating conditions. Stronger hyperfine decoupling in the optically pumped 2(3)S state is observed to systematically lead to slower build-up of He-3 orientation in the ground state, as expected. The nuclear polarizations obtained at 4.7 T still decrease at high pressure but in a less dramatic way than observed at 2 T in the same sealed glass cells. To date, thanks to the linear increase in gas density, they correspond to the highest nuclear magnetizations achieved by MEOP in pure He-3 gas. The improved efficiency puts less demanding requirements for compression stages in polarized gas production systems and makes high-field MEOP particularly attractive for magnetic resonance imaging of the lungs, for instance.