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1.
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.
Based on measurements of the temperature dependence of 3He relaxation in a wide range of spin-exchange optical pumping cells, we report evidence for a previously unrecognized surface relaxation process. The relaxation rate was found to be linearly proportional to the alkali-metal density with a slope that exceeds the spin-exchange rate, which limits the polarization for current applications, including neutron spin filters, polarized targets, and polarized gas magnetic resonance imaging. We find that the magnitude of this excess relaxation can vary widely between cells, and that the variation is larger for cells of higher surface to volume ratio. We have observed 3He polarization as high as 81%, but further improvements require understanding the origin of this relaxation.  相似文献   

3.
High-sensitivity atomic magnetometer unaffected by spin-exchange relaxation   总被引:1,自引:0,他引:1  
Alkali-metal magnetometers compete with SQUID detectors as the most sensitive magnetic field sensors. Their sensitivity is limited by relaxation due to spin-exchange collisions. We demonstrate a K magnetometer in which spin-exchange relaxation is completely eliminated by operating at high K density and low magnetic field. Direct measurements of the signal-to-noise ratio give a magnetometer sensitivity of 10 fT Hz(-1/2), limited by magnetic noise produced by Johnson currents in the magnetic shields. We extend a previous theoretical analysis of spin exchange in low magnetic fields to arbitrary spin polarizations and estimate the shot-noise limit of the magnetometer to be 2x10(-18) T Hz(-1/2).  相似文献   

4.
Krasnoperov  E.  Meilikhov  E. E.  Baines  C.  Herlach  D.  Solt  G.  Zimmermann  U.  Eshchenko  D. 《Hyperfine Interactions》1996,97(1):347-355
Muon spin relaxation in solid3He depends non-monotonously on the temperature. It is shown that this is entirely due to the magnetic dipole-dipole interactions. The observed line narrowing cannot be explained by the mechanism of positive charge hopping described by an Arrhenius-like law. The relaxation rate at low temperatures was found to increase under the influence of an external electric field.  相似文献   

5.
伏吉庆  杜鹏程  周庆  王如泉 《中国物理 B》2016,25(1):10302-010302
The laser-pumped potassium spin-exchange relaxation free(SERF) magnetometer is the most sensitive detector of magnetic field and has many important applications. We present the experimental results of our potassium SERF magnetometer. A pump–probe approach is used to identify the unique spin dynamics of the atomic ensemble in the SERF regime.A single channel sensitivity of 8 f·THz-1/2is achieved with our SERF magnetometer.  相似文献   

6.
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   

7.
Spin-lattice relaxation times T 1 were measured for solid 3He at temperatures of 0.22 to 0.73 K in a 44-Oe magnetic field. An increase in T 1 at temperatures higher than approximately 0.4 K was related to switching on the vacancy mechanism of atomic mobility in the crystal. At a melting curve minimum, in the region of predominance of exchange motions of atoms in the crystal, measurements of T 1 were performed in magnetic fields of 2 to 71 Oe. The data obtained in fields higher than 5 Oe were in agreement with the Cowan-Fardis theory.  相似文献   

8.
A transverse relaxation determination of spin-exchange relaxation free(SERF) magnetometer based on polarization modulation technique is proposed. Compared with the radio-frequency(RF) excitation and light intensity excitation methods used in SERF magnetometer, the light polarization modulation method has a high stability in low-frequency range,which indicates a more accurate transverse relaxation measurement.  相似文献   

9.
10.
Transient nuclear magnetic resonance measurements of spin-lattice and spin-spin relaxation times have been carried out as a function of temperature and pressure on 3He adsorbed on two types of commercial zeolite. In addition, the number of atoms adsorbed on unit weights of zeolite was determined by spin counting. Mechanisms for spin-spin relaxation were provided by dipole interactions among helium spins and spin-lattice relaxation was probably due to atomic motion.  相似文献   

11.
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   

12.
13.
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   

14.
In this second in a series of three papers on wall relaxation of 3He-spins we discuss relaxation in metal-coated glass cells in terms of hyperfine coupling to paramagnetic conduction electrons at the Fermi surface. This scales with the square of the work function of the coating and thereby also with its He-adsorption energy. In this sense we investigate coatings with particularly low work function and adsorption energy, namely Cs and Cs-suboxides. Although we observe a suppression of relaxation rates by two orders of magnitude as compared to bare Pyrex and fused silica walls, their temperature dependence still shows the same Arrhenius dependence as observed for bare substrates, instead of a T 3/2 dependence expected for a metallic surface. From this finding we conclude that, on one hand, the surface coverage is not complete and, on the other hand, the relaxation at the alkali surface itself is extremely slow. This finding is supported, too, by a semi-empirical estimate based on measured relaxation rates at ordinary metal surfaces, rescaled then with the respective dependence on adsorption energy.  相似文献   

15.
In this first in a series of three papers on wall relaxation of spin polarized, gaseous 3He we investigate both by theory and by experiment surface-induced spin relaxation due to paramagnetic sites in the containing glass. We present experimental and theoretical evidence that — contrary to the traditional opinion — distant dipolar coupling to paramagnetic impurities in the glass, in particular iron ions, cannot be the dominant relaxation mechanism of 3He-spins, although iron dominates the bulk static permeability. Instead dangling-bond type defects in the glass matrix are found to interact much stronger via the isotropic Fermi contact interaction. A model of paramagnetic site controlled 3He relaxation including the Fermi contact interaction is presented. With reasonable semi-empirical assumptions our model allows to describe satisfactorily the measured relaxivities, both in the dissolution-dominated regime of fused silica or borosilicate glasses of the Pyrex type as well as in the surface dominated situation of aluminosilicate glasses which have only a low permeability for He atoms. In a large sample of 1.1 litre cells, built from various aluminosilicate glasses, an average relaxation time of 150 h is reached in case contaminant ferromagnetic particles have been demagnetized beforehand. From the maximum observed value of 250 h we derive after subtraction of dipolar relaxation in the gas phase a paramagnetic surface relaxivity of ρ<0.005 cm/h at room temperature.  相似文献   

16.
We compare the cross sections for the transitions changing the projection of the total angular momentum of N2 +(2Σ) in collisions with 3He and 4He at very low collision energy. The fundamental states of the two nuclear spin isomers of N2 + are considered as well as the two fine structure levels of the first excited para level N=2. It is shown that the two fundamental states of the two nuclear spin isomers behave differently. For the fundamental para level N=0 of N2 +, the projection changing cross section is always negligible compared to the elastic one for both He isotopes. For the fundamental ortho level N=1 of N2 +, the spin-rotation interaction couples the different spin levels directly so the spin relaxation becomes a first order process. The associated resonances increase the projection changing cross section which remains smaller but becomes comparable with the elastic one. This is in contrast with the excited rotational levels of N2 +, which for the rotational deactivation and elastic channels are found to be equal around the resonances for the collisions involving 3He. These two channels are always larger than the projection changing one. We also find that, for transitions involving the fundamental rotational state, the domain of validity of the threshold laws discussed by Krems and Dalgarno [Phys. Rev. A 67, 050704 (2003)] for a potential decreasing faster than 1/r2 is shortened, due to the long range charge induced dipole potential. This effect is illustrated for the collisions of 3He with the fundamental para state of N2 +.  相似文献   

17.
18.
A reversal of the recovery of the magnetization following an rf pulse has been observed in superfluid 3HeA in 306 Oe. The time difference between the end of the rf pulse and the start of the magnetization reversal is found to be proportional to both (1 ? T/Tc)?12 and the magnitude of the initial rotation angle θ.  相似文献   

19.
宫明艳  许小涛  凤尔银 《中国物理 B》2011,20(11):113401-113401
Collisions of cold and ultracold BH in the v=0 level with the He atom are investigated using the quantum mechanical scattering formulation. The elastic and the inelastic cross sections are calculated using the two-dimensional ab initio potential energy surface. It is shown that the elastic cross section is larger than the inelastic one. When the collision energy is very low, the elastic cross section follows the Wigner threshold law and is one order of magnitude larger than that of He-O2, while it is much smaller than that of He-H2. The efficiency of the rotationally quenching state is given. The Δj=-1 transition is most efficient. The resonances are also found to occur at about the same translational energy (0.1-1 cm-1), which gives rise to steps in the rate coefficient at temperatures around 0.1-1 K.  相似文献   

20.
《Physics letters. A》1987,123(8):417-420
The surface relaxation time Tls has been investigated in solid, liquid and adsorbed 3He in porous glasses for a wide frequency range by using pulsed SQUID-NMR. ALL Tls agreed with each other and were proportional to the frequency at least at low frequencies. A model is proposed to explain the above results of Tls.  相似文献   

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