Optical Pumping and Spin Exchange in Gas Cells

This chapter reflects on the current status of optical pumping and spin exchange in gas cells. Optical pumping is a method to produce population imbalances among the ground or excited state sublevels of atoms, and molecules by the interaction between the atomic system and light. In the preceding examples, any spin polarization of the atomic vapor generated by the pumping light is along the direction of the static magnetic field. This is called “longitudinal pumping.” Transverse optical pumping occurs when the pumping light generates an atomic polarization along a direction perpendicular to the static magnetic field. As depopulation pumping relies on the different pumping rates out of different sublevels, the efficiency of depopulation pumping depends on the polarization and spectral profile of the pumping light. In addition to directly polarizing an atom by optical pumping, it is possible to polarize atoms by spin-transfer collisions. Spin-exchange collisions will always be present in any polarized vapor and can be very important, especially for paramagnetic atoms such as alkali atoms.