Optically Polarized $^3$He

TL;DR

This review discusses the physics, technology, and recent advancements in producing highly spin-polarized $^3$He nuclei using optical pumping methods, highlighting improvements, new phenomena, and diverse applications.

Contribution

It provides a comprehensive overview of recent technological developments and experimental findings in optical pumping techniques for hyperpolarized $^3$He.

Findings

Spectrally narrowed lasers and Rb/K mixtures enhance polarization and rate in SEOP.

High magnetic fields in MEOP increase pressure capabilities and reveal light-induced relaxation.

New relaxation dependencies on temperature and magnetic field have been observed.

Abstract

This article reviews the physics and technology of producing large quantities of highly spin-polarized, or hyperpolarized, $^3$He nuclei using spin-exchange (SEOP) and metastability-exchange (MEOP) optical pumping, and surveys applications of polarized $^3$He. Several recent developments are emphasized for each method. For SEOP, the use of spectrally narrowed lasers and Rb/K mixtures has substantially increased the achievable polarization and polarizing rate. MEOP in high magnetic fields has likewise significantly increased the pressure at which this method can be performed, and has led to the observation of a light-induced relaxation mechanism. In both methods the increased capabilities have led to more extensive study and modeling of the basic underlying physics. New unexplained dependences of relaxation on temperature and magnetic field have been discovered in SEOP cells. Applications of both methods are also reviewed, including targets for charged particle and photon beams, neutron spin filters, magnetic resonance imaging, and precision measurements.