Optical pumping of Helium-3 in a high magnetic field
Dr. Pierre Jean Nacher (Laboratoire Kastler Brossel, ENS Paris)

We have demonstrated that operation in a strong magnetic field (1.5 Tesla) allows to extend the useful range of metastability exchange optical pumping of helium 3 to unusually high pressures (e.g. 56% nuclear polarisation at 32 mbar and 37% at 67 mbar). We have investigated this new optical pumping scheme experimentally and theoretically in order to understand the relevant underlying mechanisms, and in particular to probe the consequences of the strong hyperfine decoupling in such a high field. The advantages and limitations of using a high field will be discussed, in particular in the context of lung MRI with hyperpolarized helium 3, for which this new technique may lead to significant simplifications.