W. Happer

High‐volume production of laser‐polarized 129Xe

A method is described for producing several liters of nuclear spin polarized 129Xe gas via spin exchange with an optically pumped Rb vapor. We use a 140 W AlGaAs laser diode array whose broad spectral output is efficiently absorbed by employing ∼10 atm of 4He to pressure broaden the Rb D1 absorption profile. 129Xe is polarized in a continuous gas flow and is then cryogenically accumulated and stored. Extensions of this technique should enable the production of tens of liters of 129Xe with a nuclear spin polarization of order 50%. Production of laser‐polarized 129Xe in liter quantities is important for the continued development of magnetic resonance imaging using spin‐polarized 129Xe.

EDGE ENHANCEMENT OBSERVED WITH HYPERPOLARIZED 3HE

Abstract We have produced one-dimensional (1-D) magnetic resonance images of hyperpolarized 3He in square glass cells and demonstrated edge enhancement of the signal intensity near the parallel impermeable boundaries. The size and position of the edge-enhancement peaks approximately agrees with the theoretical prediction based on solutions of the 1-D Torrey equation with boundary conditions. Additional distortion in our images is due to the long-range dipole fields produced by the polarized spins and by the bulk magnetic susceptibility of the glass. Our experiments, done in an applied field of H0 = 31 G, demonstrate the low-field imaging capacity of hyperpolarized noble gases.

CROSS-RELAXATION IN LASER-POLARIZED LIQUID XENON

Abstract By dissolving compounds in hyperpolarized liquid Xe, we have successfully transferred the 129 Xe polarization to other spins in solution. We have observed signal enhancements of over 45 for 1 H, and over 70 for 13 C, compared to their thermal polarization signals at 200 K and 1.4 T. The lifetimes of the enhancements are on the order of 20 min. In addition, in dissolved toluene we have seen preferential enhancement of the ring protons over the methyl protons.

Wall relaxation of spin polarized 129Xe nuclei

Abstract The wall relaxation of spin polarized 129 Xe nuclei is much longer in silicone coated pyrex cells than in uncoated cells. In contrast to uncoated glass cells where the wall relaxation times are unpredictable and usually only a few tens of seconds, the relaxation time of 129 Xe in silicone-coated cells is usually 20 minutes or longer.

Plasma production in a Cs vapor by a weak CW laser beam at 6010 Å

Abstract When a dye laser beam at 6010.5 A (which excites the Cs 6 2 P 1 2 →8D 3 2 transition), of power 0.1 W, is focused into a Cs vapor of density ≳ 10 17 cm -3 , we observe a bright localized white glow near the laser focus. Our experiments indicate that this glow is due to the production of a Cs plasma, which exhibits many characteristics of a discharge plasma, like emission of numerous atomic lines and of recombination continua, plasma-broadening of atomic lines, and hysterisis. This laser-produced plasma is in Saha equilibrium with a typical electron density of 3 × 10 14 cm -3 , and a typical electron temperature of 0.2 eV.

AN OPTICAL PUMPING PRIMER

This pedagogical paper introduces the basic ideas of optical pumping. Some of the various optical pumping mechanisms are discussed, and illustrated by diagrams showing the experimental apparatus. The density matrix formalism is introduced and used to quantitatively examine the effects of optical pumping. Next some of the various spin relaxation mechanisms such as collisions and spin exchange between electrons and nuclei, are discussed. A good knowledge of elementary quantum mechanics is needed to follow the article.

Observation of the lowest triplet transitions 3Σ+g–3Σ+u in Na2 and K2

We report here the observation and definite identification of the lowest triplet transition 3Σ+g–3Σ+u in Na2 and K2. The identification of these bands is based upon direct comparison of K2 absorption, thermal emission, and laser‐induced fluorescence, and Na2 laser‐induced fluorescence, with spectra calculated from recent, accurate, ab initio potential curves. These data also serve as a sensitive check on the accuracy of these potentials.

Electrolytic fabrication of atomic clock cells

This paper describes an electrolytic method to fill alkali metal into miniature cells made with anodically bonded silicon wafer and Pyrex glass windows

Neutron polarization with polarized 3He

Abstract An effective polarizer for thermal and epithermal neutrons is possible with polarized, high density, gaseous 3 He. We describe the technique of 3 He polarization by spin exchange with laser optically pumped Rb vapor which can provide 6 cm 3 of > 70% polarized 3 He at a density of 3×10 20 atoms cm −3 (10 atm at STP). The 3 He polarization can be rapidly reversed, a requirement for sensitive symmetry tests.

LASER-POLARIZED LIQUID XENON

Abstract We present the first liquid-phase studies of hyperpolarized Xe, Xe in which the polarization of 129 Xe is much greater than thermal. Using grams of Xe of natural isotopic composition with 6% polarization of the 129 Xe, we examined the lifetime of the 129 Xe polarization in the liquid as a function of field and temperature. Our measurements showed that surface effects make a significant contribution to the relaxation rate. Lifetimes in excess of 30 min were observed. The long lifetimes and high polarization present several new applications for liquid Xe.