Spin exchange optical pumping at pressures near 1 bar for neutron spin filters

Abstract

Motivated by applications to neutron spin filters and recent advances in spectrally narrowed laser diode arrays (LDAs), we are exploring spin exchange optical pumping of He3 at pressures near 1 bar. Among our more interesting results has been the production of glass cells with extremely long relaxation times. The best of these has a lifetime of T1=840 h [where the polarization decays versus time, t, as exp(−t/T1)], dominated by the dipole–dipole contribution of 950 h at a He3 partial pressure of 0.85 bar. Using a broadband LDA, we have obtained 55% He3 nuclear polarization in this cell. These results are particularly relevant to the application of He3-based neutron spin filters to neutron scattering and weak interaction experiments. Applications to magnetometry and polarized gas magnetic resonance imaging are also possible.