共查询到20条相似文献,搜索用时 0 毫秒
1.
Babcock E Nelson I Kadlecek S Driehuys B Anderson LW Hersman FW Walker TG 《Physical review letters》2003,91(12):123003
We demonstrate spin-exchange optical pumping of 3He using a "hybrid" K-Rb vapor mixture. The Rb atoms absorb light from a standard laser at 795 nm, then collisionally polarize the potassium atoms. Spin-exchange collisions of K and 3He atoms then transfer the angular momentum to the 3He with much greater efficiency than Rb-3He. For a K-rich vapor, the efficiency of the hybrid spin-exchange collisions approaches 1/4, an order of magnitude greater than achieved by pure Rb pumping. We present the first measurements of actual photon efficiencies (polarized nuclei produced per absorbed photon), and show that a new parasitic absorption process limits the total efficiencies for both hybrid and pure Rb pumping. 相似文献
2.
Wai Tung Lee Xin Tong Dennis Rich Yun Liu Michael Fleenor Akbar Ismaili Joshua Pierce Mark Hagen Jonny Dadras J. Lee Robertson 《Physica B: Condensed Matter》2009,404(17):2670-2672
In recent years, polarized 3He gas has increasingly been used as neutron polarizers and polarization analyzers. Two of the leading methods to polarize the 3He gas are the spin-exchange optical pumping (SEOP) method and the meta-stable exchange optical pumping (MEOP) method. At present, the SEOP setup is comparatively compact due to the fact that it does not require the sophisticated compressor system used in the MEOP method. The temperature and the laser power available determine the speed, at which the SEOP method polarizes the 3He gas. For the quantity of gas typically used in neutron scattering work, this speed is independent of the quantity of the gas required, whereas the polarizing time using the MEOP method is proportional to the quantity of gas required. Currently, using the SEOP method to polarize several bar-liters of 3He to 70% polarization would require 20−40 h. This is an order of magnitude longer than the MEOP method for the same quantity of gas and polarization. It would therefore be advantageous to speed up the SEOP process. In this article, we analyze the requirements for temperature, laser power, and the type of alkali used in order to shorten the time required to polarize 3He gas using the SEOP method. 相似文献
3.
Control of magnetization plays an important role in the scientific and technological field of manipulating spin systems. In this work, we study the problem of manipulating nuclear magnetization in the spin-exchange optical pumping system, including accelerating the recovery of nuclear polarization and fixing it on a specific desired state. A real-time feedback control strategy is exploited here. We have also done some numerical simulations, with the results clearly demonstrating the effectiveness of our method, that the nuclear magnetization is able to be driven towards the equilibrium state at a much faster speed and also can be stabilized to a target state. We expect that our feedback control method can find applications in gyro experiments. 相似文献
4.
We present in situ measurements of temperatures inside multi-atmosphere spin-exchange optical pumping cells using Raman scattering from the N2 quenching gas. Under conditions usually prevailing in spin-exchange optical pumping experiments, we find that gas temperatures can be elevated hundreds of degrees above ambient, and that convection plays a very important role in the heat transport of the system. 相似文献
5.
E. Stoltz M. Meyerhoff N. Bigelow M. Leduc P. -J. Nacher G. Tastevin 《Applied physics. B, Lasers and optics》1996,63(6):629-633
New diode lasers delivering 50 mW output power at 1083 nm are shown to be efficient sources for optical pumping of helium. They can polarize nuclei in a3He gas up toM = 50% over the pressure range 0.4–1.6 torr. Larger nuclear polarizationsM of3He nuclei, of order 80%, can be obtained in3He-4He mixtures when the laser frequency is tuned to a4He line. A standard optical measurement of nuclear polarizationM has been extended to the case of3He-4He mixtures. The effect of various parameters on the steady-state polarizationM and on the pumping timeT
p is discussed.Laboratoire associé au Centre National de la Recherche Scientifique et à l'Université P. M. Curie 相似文献
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The 3He longitudinal spin-relaxation rate T1-1 is crucial for production of highly polarized 3He by spin-exchange optical pumping. We show that T1-1 is increased by a factor of 2-20 solely by exposure of spin-exchange cells to a few-kG magnetic field. The original T1-1 can be restored by degaussing the cell. The effect is attributed to magnetic surface sites and has been observed in both Pyrex and aluminosilicate-glass cells. Our results both advance the understanding of wall relaxation and demonstrate the use of 3He as an extremely sensitive probe of surface magnetism. 相似文献
8.
Y. Arimoto T. InoH.M. Shimizu T. KamiyamaH. Kira T. OkuY. Sakaguchi K. KakuraiK. Sakai J. SuzukiS. Koizumi M. AraiY. Endo M. NakamuraT. Shinohara M. TakedaS. Wakimoto D. YamazakiK. Ohoymama H. HirakaK. Yamada K. TsutsumiL.-J. Chang 《Physica B: Condensed Matter》2011,406(12):2439-2442
Polarized neutron spin filters are being developed based on spin-exchange optical pumping. In the present study a high-power diode laser (85 W) was used to excite Rb atoms and the laser linewidth was narrowed using an external cavity. The optics in the external cavity were designed by ray tracing. The ray-trace calculations demonstrated that a doublet lens in front of the laser eliminates aberrations. The maximum spectral peak height in the doublet optics was found to be 25% higher than for a singlet lens. 相似文献
9.
Junpei Zhang Chuyi Huang Zecong Qin Fan Ye Syed Mohd Amir Ahmed Salman Yuchen Dong Long Tian Zachary Norris Buck Wolfgang Kreuzpaintner Matthew Musgrave Xin Qi Tianhao Wang Xin Tong 《中国科学:物理学 力学 天文学(英文版)》2022,(4)
In this paper,we present the performance of a recently developed in-situ spin-exchange optically pumped3He-neutron spin filter system at the China Spallation Neutron Source(CSNS).The system achieved a3He polarization of over 74%at the beamline BL-20.Analysis of neutron transmission experiment results reveals a neutron polarization of>90%and an average transmission of 27%for 2.2?neutrons,which were maintained for a duration of 120 h of beam time.To the best of our knowledge,this is the first in-situ hyperpolarized3He system incorporated on a neutron beamline in China.This technology is expected to provide stable,wide-angle,and highly polarized neutrons at the CSNS for materials research and fundamental neutron physics. 相似文献
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K. Suchanek M. Suchanek A. Nikiel T. Pałasz M. Abboud A. Sinatra P.-J. Nacher G. Tastevin Z. Olejniczak T. Dohnalik 《The European physical journal. Special topics》2007,144(1):67-74
An accurate optical method to measure the nuclear
polarization of 3He atoms in the 11S ground state is
described. The absorption of a weak, probe laser beam is used to
measure the relative populations of two hyperfine sublevels of the
23S metastable state that are not addressed by the pumping
laser beam. Since a common spin temperature between the ground and
metastable states is established by metastable exchange
collisions, the nuclear polarization can be derived from these
absorption measurements. The method is highly sensitive, robust,
and can be used to monitor the dynamics of optical pumping and
relaxation processes without interfering with them. It was
successfully implemented and tested in the 0.45–2.0 T magnetic
field range at the 3He gas pressure up to 67 mbar. 相似文献
12.
Y. Arimoto N. Shimakura K. Yonehara T. Yamagata M. Tanaka 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,8(3):305-308
The spin-exchange cross-section, , was measured for a 6.33 keV/amu He ion incident on a polarized Rb atom. The result is cm2, which is unexpectedly an order of magnitude smaller than the theoretical value cm2 evaluated by the semiclassical impact parameter method assuming formation of a single molecular state.
Received 11 September 1999 and Received in final form 28 December 1999 相似文献
13.
T. Dohnalik B. Głowacz Z. Olejniczak T. Pałasz M. Suchanek A. Wojna 《The European physical journal. Special topics》2013,222(9):2103-2118
The Magnetic Resonance Imaging (MRI) of human lungs for diagnostic purposes became possible by using nuclear spin hyperpolarized noble gases, such as 3He. One of the methods to polarize 3He is the Metastability Exchange Optical Pumping (MEOP), which up to now has been performed at low pressure of about 1 mbar and in low magnetic field below 0.1 T (standard conditions). The equilibrium nuclear polarization can reach up to 80%, but it is dramatically reduced during the subsequent gas compression to the atmospheric pressure that is necessary for the lungs examination. Further polarization losses occur during the transportation of the gas to the hospital scanner. It was shown recently that up to 50% polarization can be obtained at elevated pressure exceeding 20 mbar, by using magnetic field higher than 0.1 T (nonstandard conditions). Therefore, following the construction of the low-field MEOP polarizer located in the lab, a dedicated portable unit was developed, which uses the magnetic field of the 1.5 T MR medical scanner and works in the continuous-flow regime. The first in Poland MRI images of human lungs in vivo were obtained on the upgraded to 3He resonance frequency Siemens Sonata medical scanner. An evident improvement in the image quality was achieved when using the new technique. The paper shows how spectroscopic measurements of 3He carried out in various experimental conditions led both to useful practical results and to significant progress in understanding fundamental processes taking place during MEOP. 相似文献
14.
Hayley Newton Laura L. Walkup Nicholas Whiting Linda West James Carriere Frank Havermeyer Lawrence Ho Peter Morris Boyd M. Goodson Michael J. Barlow 《Applied physics. B, Lasers and optics》2014,115(2):167-172
Spin-exchange optical pumping (SEOP) has been widely used to produce enhancements in nuclear spin polarisation for hyperpolarised noble gases. However, some key fundamental physical processes underlying SEOP remain poorly understood, particularly in regards to how pump laser energy absorbed during SEOP is thermalised, distributed and dissipated. This study uses in situ ultra-low frequency Raman spectroscopy to probe rotational temperatures of nitrogen buffer gas during optical pumping under conditions of high resonant laser flux and binary Xe/N2 gas mixtures. We compare two methods of collecting the Raman scattering signal from the SEOP cell: a conventional orthogonal arrangement combining intrinsic spatial filtering with the utilisation of the internal baffles of the Raman spectrometer, eliminating probe laser light and Rayleigh scattering, versus a new in-line modular design that uses ultra-narrowband notch filters to remove such unwanted contributions. We report a ~23-fold improvement in detection sensitivity using the in-line module, which leads to faster data acquisition and more accurate real-time monitoring of energy transport processes during optical pumping. The utility of this approach is demonstrated via measurements of the local internal gas temperature (which can greatly exceed the externally measured temperature) as a function of incident laser power and position within the cell. 相似文献
15.
We present new quantum Monte Carlo calculations of the ground-state energy of liquid 3He using backflow and 3-body wavefunctions and twist-averaged boundary conditions. We estimate the effects of the 3-body potential and compare to experimental measurements of the unpolarized equation of state and the magnetic susceptibility. There is still a large discrepancy with respect to the magnetic susceptibility, requiring either improved nodal surfaces or going beyond the fixed-node method. 相似文献
16.
We report on optical pumping experiments in helium-3 using a new broad-band, all fiber laser at 1083 nm. The kinetics of polarization
build-up are compared to the numerical results of an appropriate model. Effects of laser power and bandwidth are discussed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
17.
We measured laser-induced-fluorescence (LIF) and beam-depletion (BD) spectra of rubidium atoms (5S-5P transition) on the surface of superfluid helium nanodroplets (M-He_{N} with M=Rb). It is known that when M is a lighter alkali atom electronic excitation always leads to detachment of the excited atom (M;{*}). The dissociation energy, few tens cm;{-1}, comes either as photon excess energy or from the barrierless formation of a M;{*}-He exciplex. We observe that this picture does not hold when M=Rb and the photon excess energy is small: we are able to excite atoms without detaching them from the droplet, thanks to a barrier preventing formation of the exciplex. This system is ideally suited for optical spin pumping in a He nanodroplet, whose achievement we explicitly demonstrate in a pump-probe magnetic circular dichroism experiment. 相似文献
18.
Whiting N Nikolaou P Eschmann NA Goodson BM Barlow MJ 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2011,208(2):298-304
The (129)Xe nuclear spin polarization (P(Xe)) that can be achieved via spin-exchange optical pumping (SEOP) is typically limited at high in-cell xenon densities ([Xe](cell)), due primarily to corresponding reductions in the alkali metal electron spin polarization (e.g. P(Rb)) caused by increased non-spin-conserving Rb-Xe collisions. While demonstrating the utility of volume holographic grating (VHG)-narrowed lasers for Rb/(129)Xe SEOP, we recently reported [P. Nikolaou et al., JMR 197 (2009) 249] an anomalous dependence of the observed P(Xe) on the in-cell xenon partial pressure (p(Xe)), wherein P(Xe) values were abnormally low at decreased p(Xe), peaked at moderate p(Xe) (~300 torr), and remained surprisingly elevated at relatively high p(Xe) values (>1000 torr). Using in situ low-field (129)Xe NMR, it is shown that the above effects result from an unexpected, inverse relationship between the xenon partial pressure and the optimal cell temperature (T(OPT)) for Rb/(129)Xe SEOP. This interdependence appears to result directly from changes in the efficiency of one or more components of the Rb/(129)Xe SEOP process, and can be exploited to achieve improved P(Xe) with relatively high xenon densities measured at high field (including averaged P(Xe) values of ~52%, ~31%, ~22%, and ~11% at 50, 300, 500, and 2000 torr, respectively). 相似文献
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