Optical pumping of helium-3 at high pressure in a 1.5 Tesla magnetic field

We present an experimental and theoretical study of metastability exchange optical pumping of helium-3 in a 1.5 Tesla magnetic field in the pressure range 1-67 mbar. A systematic experimental study has allowed to determine good conditions for efficient optical pumping. At 1.5 Tesla, high nuclear polarizations and fast pumping rates are achieved at high pressure. This extends the domain of applicability of metastability exchange optical pumping. A realistic model allows to discuss the effects of the various involved processes on the efficiency of optical pumping. We show that, in spite of the hyperfine decoupling, optical pumping at 1.5 Tesla retains the high photon efficiency of usual metastability exchange optical pumping. The comparison between experimental and theoretical values of nuclear polarization reveals a relaxation process whose rate increases with the population of the 2³P excited state and with the pressure. (author)