We measure nuclear and electron spin-polarized H and D densities of at least 10^{19}  cm^{-3} with ∼10  ns lifetimes, from the photodissociation of HBr and DI with circularly polarized UV light pulses. This density is ∼6 orders of magnitude higher than that produced by conventional continuous-production methods and, surprisingly, at least 100 times higher than expected densities for this photodissociation method. We observe the hyperfine quantum beating of the H and D magnetization with a pickup coil, i.e., the respective 0.7 and 3 ns periodic transfer of polarization from the electrons to the nuclei and back. The 10^{19}  cm^{-3} spin-polarized H and D density is sufficient for laser-driven ion acceleration of spin-polarized electrons, protons, or deuterons, the preparation of nuclear-spin-polarized molecules, and the demonstration of spin-polarized D-T or D-^{3}He laser fusion, for which a reactivity enhancement of ∼50% is expected.

Recently, our group produced spin-polarized hydrogen (SPH) atoms at densities of at least 1019 cm−3 from the photodissociation of hydrogen halide molecules with circularly polarized UV light and measured them via magnetization-quantum beats with a pickup coil. These densities are approximately 7 orders of magnitude higher than those produced using conventional methods, opening up new fields of application, such as ultrafast magnetometry, the production of polarized MeV and GeV particle beams, such as electron beams with intensities approximately 104 higher than current sources, and the study of polarized nuclear fusion, for which the reaction cross sections of D–T and D–3He reactions are expected to increase by 50% for fully polarized nuclear spins. We review the production, detection, depolarization mechanisms, and potential applications of high-density SPH.

We present a compact polarimeter, which can perform sensitive measurements of optical rotation in vapor. The operation of the polarimeter is based a Cavity Ring-Down scheme which employs two signal reversals, which increase sensitivity and reduce noise, allowing the realization of sensitive measurements in the presence of spurious birefringence. We describe the operation of the polarimeter, give the basic equations for the signal analysis and retrieval of optical rotation angle, and present measurements that demonstrate a sensitivity of ~80 μdeg/pass.