Chapter 6: Spin-exchange Optical Pumping at High Xenon Densities and Laser Fluxes: Principles and Practice

Over the last two-plus decades, hyperpolarized (HP) ¹²⁹Xe has been exploited for a wide range of magnetic resonance applications. HP ¹²⁹Xe is usually created by spin-exchange optical pumping (SEOP). This chapter reviews efforts in our laboratories and those of our collaborators to explore HP ¹²⁹Xe generation via SEOP in the demanding regimes of high xenon densities and resonant laser powers. Of particular importance is the technical development of high-power frequency-narrowed laser sources which, combined with fundamental studies, have enabled high ¹²⁹Xe polarizations to be achieved at relatively high Xe densities under conditions of stopped-flow production. Efforts exploring the interplay between gas mixture, laser power, laser wavelength, and cell temperature in determining ¹²⁹Xe polarization efficiency have led to the development of automated, clinical-scale ¹²⁹Xe “hyperpolarizers” capable of generating significant quantities of ¹²⁹Xe with near-unity polarization and without the need for cryogenic collection—including an “open-source” design approved and demonstrated for human use, and an improved design centered around a 3-D printed oven. Another area of interest is how the high resonant laser energy is absorbed, thermalized, and dissipated during SEOP. The potential advantages of using Cs instead of—or in addition to—Rb as the alkali metal are also explored.