Mingxin Zhao

Laser-enhanced low-pressure gas NMR signal from 129Xe

Abstract We have greatly enhanced the nuclear magnetic resonance signal of low-pressure gas ( 15 Torr of 129 Xe) on an NMR spectrometer with linearly polarized laser radiation. An amplification factor of the nuclear polarization is of the order of magnitude of 10 4 as compared with the Boltzmann polarization in the same magnetic field.

Synthesis and ab initio X-ray powder diffraction structure of the new alkali and alkali earth metal borate NaCa(BO3).

A sodium calcium borate, NaCaBO3, has been synthesized by the solid-state reaction method and the structure solved from X-ray powder diffraction data. The compound crystallizes in space group Pmmn and has a desired structure type containing isolated planar BO3(3-) anions. Mixed occupancy is found to exist in the Ca site, with partial replacement by Na. One Ca/Na mixed atom and one Na atom are at sites with mm2 symmetry, and a second Ca/Na mixed atom, an Na atom, two B and two O atoms are on mirror planes.

NMR study of low-pressure 129Xe gas

Abstract The enhanced 129 Xe gas (15 Torr) NMR signal has been observed on a Varian XL-200 NMR spectrometer with spin-exchange optical pumping. An amplification factor of the nuclear spin polarization of gaseous 129 Xe is of the order 10 3 times the Boltzmann polarization at 60°C. The binary spin-exchange cross section for Csue5f8 129 Xe has been measured by observing the nuclear spin relaxation of 129 Xe in the presence of Cs vapor. The measured cross section is (1.7 ± 0.2) × 10 −20 cm 2 . The effect of diffusion of 129 Xe atoms on NMR signals is also discussed.

A fast efficient passive cesium ARF

Abstract The properties of a passive cesium ARF (atomic resonance filter) are determined predominantly by the physical processes of absorption, emission and internal energy conversion in the cesium vapor. A fast efficient passive cesium ARF at 455 nm and 459 nm is demonstrated by the method of mixing molecular gas in the cesium vapor. The nominal maximum information rate of the passive cesium ARF, which is an important parameter for laser communication applications, is estimated by the fwhm (full width at half maximum) of the time-resolved fluorescence spectrum of its output emission at 852 nm.

Frequency-selective laser optical pumping and spin exchange of cesium with Xe-129 and Xe-131 in a high magnetic field

We report the experimental results of frequency-selective laser optical pumping and spin exchange of Cs with129Xe and131Xe in a high magnetic field of 11.74 T. Our results show that hyperpolarized129Xe and131Xe nuclear magnetic resonance (NMR) signals exhibit alternating phases when the laser frequency for pumping the cesium atoms is changed, which is explained on the basis of the high-field optical pumping of Cs. We obtain about 3% polarization of the129Xe. The electron-spin polarization of the Cs atoms has been measured to be about 22% with a simple NMR method.

Anomalous relaxation of populations in hyperfine Zeeman sublevels of Cs atoms induced by collisional modification of the Cs hyperfine interaction

Cs vapour in , Ar, Kr, Ne, He and Xe buffer gases was optically pumped with a diode laser in a magnetic field of 1.516 T. The relaxation of the population imbalance in the hyperfine Zeeman sublevels of the ground state was detected with another diode laser. A phenomenological theory is presented which explains the optical transients and the time variation of the populations in the hyperfine Zeeman sublevels. Both experimental and theoretical results showed that there were relaxation transients of populations in some hyperfine Zeeman sublevels of optically pumped Cs with `anomalous shapes. The experimental results showed that the `anomalous relaxation depended strongly on the buffer-gas species and the buffer-gas pressure. Theoretically, it was found that the combined electron-spin - nuclear-spin transition, which is mainly induced by collisional modification , caused the `anomalous shapes of the transients. The collisional transfer cross section for the binary collisional interactions was estimated to be . `Anomalous relaxations of populations in the hyperfine Zeeman sublevels are discussed. The results of the calculation are in good agreement with the experimental results.

Relaxation of populations in hyperfine Zeeman sublevels of the ground state of optically pumped Cs in a high magnetic field

Abstract Cs vapor was optically pumped with a diode laser in a magnetic field of 1.516 T. The relaxation of the population imbalance in the hyperfine Zeeman sublevels of the ground state was detected with an another diode laser. There were different population evolutions in different hyperfine Zeeman sublevels of optically pumped Cs and the relaxation transients had ‘anomalous’ shapes. It was found that the combined electron spin-nuclear spin transition caused the ‘anomalous’ shapes of the transients. We deduced the transition rates between the sublevels of the ground state from the transients. The transients required a ‘non-uniform’ model of collision relaxation on the cell wall in the rate-equation calculation.

Steady populations in hyperfine Zeeman sublevels of laser optically pumped Cs in high magnetic fields

Laser optical pumping of caesium atoms in a high magnetic field of 1.514 T is reported. Steady absorption spectra from hyperfine Zeeman sublevels are obtained with two semiconductor lasers. The populations in different hyperfine Zeeman sublevels show unusual changes when the power of the pumping laser is changed. The optical pumping and the spin flip by hyperfine interaction bring about the marching of atoms from the lowest to the highest M(I) sublevels of the ground state.