Figure 1. Schematic depicts optical pumping and spin exchange. The glass cell is filled with 3He gas and a small quantity of rubidium. Heating of the cell produces rubidium vapor. When the mixture is illuminated by laser light, absorption of the light causes high electronic polarization in the rubidium atoms by means of the process called "optical pumping." When the polarized rubidium atoms collide with the 3He atoms, the polarization is transferred to the 3He nuclei. Transfer of the polarization is referred to as "spin exchange."