Fundamentals of Spin-Exchange Optical Pumping

The standard model of Spin-Exchange Optical Pumping of ³He has come under close scrutiny as researchers try to maximize the quantity and polarization of ³He. This paper will review four important effects that have come to light: 1) pumping with frequency narrowed diode lasers significantly improves the polarization and production rate as compared to off-the-shelf broadband sources 2) Rb-K mixtures again improve the production rate due to reduced collisional loss in K-He collisions, 3) a unexplained ³He wall relaxation mechanism that scales closely with alkali vapor pressure limits the attainable ³He polarization to about 80%, 4) a small collisionally-induced breakdown in the selection rules for optical pumping explains why narrowband lasers are so advantageous, and may explain some observed limitations for Rb-K pumping as well.