Introduction

Spin-Exchange Optical Pumping (SEOP) is the process of transferring angular momentum (polarization) from an optically pumped alkali metal vapor to the nuclei in a substance of interest. The most commonly used targets for SEOP are gases like $^3$He or $^{129}$Xe, which both have spin-$\tfrac{1}{2}$ nuclei. These gases, under certain favorable conditions, can maintain their polarization for hundreds of hours (this is the longitudinal relaxation time $T_1$). In a magnetic field, these gases have an equilibrium polarization of about 2 ppm (about 499,999 spins are aligned with the field, and about 500,001 anti-aligned out of each million), but once hyperpolarized using SEOP, they can achieve up to ~50% polarization (about 250,000 aligned and 750,000 anti-aligned out of each million spins). These 'hyperpolarized' gases can then be used in many applications, including magnetic resonance imaging (MRI).

At this year's annual meeting of the American Physical Society Division of Atomic, Molecular and Optical Physics (to be held at the University of Virginia) will be a special session on Hyperpolarized materials. It's being organized by Tom Gentile of NIST.