Research Highlights

Ultrahigh-density spin-polarized H and D observed via magnetization quantum beats

Researchers at IESL-FORTH, in the Polarization Spectroscopy Laboratory, led by Prof. T. Peter Rakitzis, have produced spin-polarized hydrogen (SPH) and spin-polarized deuterium (SPD) at record densities of 1019 cm-3, near atmospheric densities, which is at least a million times higher than conventional continuous-production methods. These ultrahigh SPH and SPD densities are high enough to allow a first demonstration of polarization laser fusion (at the largest laser facilities in the world, such as NIF and Megajoule), for which a reactivity enhancement of 50% is expected for the D-T and D-3He fusion reactions. Other applications include the production of highly intense polarized proton and deuteron beams, for particle physics and nuclear physics experiments, and the preparation of hyperpolarized molecules for NMR enhancement.

Conventional continuous-production methods, such as Stern-Gerlach spin separation and spin-exchange optical pumping, are limited to SPH and SPD densities of about 1012 cm3, due to large depolarization rates. The novel approach used by FORTH researchers for producing such high SPH and SPD densities, is to do so nearly instantaneously, before there is time for depolarization, from the complete photodissociation of hydrogen halide molecules at high density, with circularly-polarized, 150 ps, UV laser pulses. The SPH and SPD lifetimes are only about 10 ns, but this is long enough for pump-probe experiments, such as needed to demonstrate polarized laser fusion.

The rapid production of large numbers of spin-polarized atoms creates a time-dependent magnetization which can be detected using a simple pick-up coil via the voltage (EMF). This EMF (see Figure) can be used to determine the number of spin-polarized atoms and their depolarization timescales. Using this detection method, the members of the Polarization Spectroscopy group at IESL-FORTH demonstrated the production of SPH and SPD densities of 1019 cm -3, and observed the respective 0.7 ns and 3 ns periodic transfer of polarization from the electrons to the nuclei and back. 

Research Article: "Ultrahigh-Density Spin-Polarized H and D Observed via Magnetization Quantum Beats​", by D. Sofikitis, C. S. Kannis, G. K. Boulogiannis, and T. P. Rakitzis, Phys. Rev. Lett. 121, 083001 (22 August 2018)

Caption: Magnetization hyperfine quantum beats in (a) deuterium and (b) hydrogen atoms. The insets show Fourier transforms of the data showing the well-known hyperfine beating frequencies for D and H.

 

October 2018

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