Enhanced polarization of electron spins inHe4by simultaneous optical pumping with circularly and linearly polarized resonance radiation

The polarization of helium (2 ${}_{}{}^3{}_{}{}^{}$ ${\mathit{S}}_1$) metastable atoms saturates at 50% when the ensemble is optically pumped with the ${\mathit{D}}_0$ (2 ${}_{}{}^3{}_{}{}^{}$ ${\mathit{S}}_{1–}$2 ${}_{}{}^3{}_{}{}^{}$ ${\mathit{P}}_0$) transition. We have obtained polarizations approaching 100% with a simple, straightforward modification to the conventional experimental arrangement. The addition of a small amount of π-polarized ${\mathit{D}}_0$ light incident on the cell perpendicular to the defining field direction doubles the polarization produced by circularly polarized ${\mathrm{\sigma }}^{+}$ light along the field direction. A simple rate-equation model illustrates the enhancement.