Metastability Exchange Optical Pumping of Helium3 at High Pressures and 1.5 T: Comparison of two Optical Pumping Transitions (original) (raw)
Related papers
Optical Pumping of Helium3 at High Pressure and Magnetic Field
Acta Physica Polonica B - ACTA PHYS POL B, 2002
At low magnetic field, the efficiency of metastability-exchange optical pumping of helium-3 is known to be optimal for pressures around 1mbar. We demonstrate on several examples (up to 32mbar) that operating in a higher magnetic field (here 0.12 T) can significantly increase the nuclear polarisations achieved at higher pressures. Since polarisation measurements cannot be made with the standard technique, we use a general optical method based on absorption measurements at 1083 nm to measure the polarisation of the atoms in the ground state.
Europhysics Letters (epl), 2004
We perform metastability exchange optical pumping of helium-3 in a strong magnetic field of 1.5 T. The achieved nuclear polarization, from 80% at 1.33 mbar to 25% at 67 mbar, shows a substantial improvement at high pressures with respect to standard low-field optical pumping. The specific mechanisms of metastability exchange optical pumping at high field are investigated, advantages and intrinsic limitations are discussed. From a practical point of view, our results open the way to alternative technological solutions for polarized helium-3 applications and in particular for magnetic resonance imaging of human lungs.
The European Physical Journal Special Topics, 2007
An accurate optical method to measure the nuclear polarization of 3 He atoms in the 1 1 S 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 2 3 S 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 3 He gas pressure up to 67 mbar.
The European Physical Journal D, 2013
Systematic studies of the metastability exchange optical pumping (MEOP) process in 3 He gas at high magnetic fields (0.45, 0.9, 1.5, and 2 T) and pressures (32 and 64 mbar) are performed. The impact of experimental parameters such as laser power, beam profile, and shape of the pumping cell is evaluated. By varying the discharge intensity in the cell, the density of metastable state atoms and the plasma-induced nuclear relaxation rate are also controlled, and their effect on the MEOP efficiency can be investigated. Very accurate experimental results are obtained, opening the way to quantitative tests of a recently proposed model of the MEOP process at high magnetic field. We report selected MEOP results with nuclear polarizations exceeding 50 % at 64 mbar and 2 T, which represents a dramatic improvement in performances over MEOP at low magnetic field. The present findings suggest that still higher polarizations can be achieved in higher magnetic fields, and motivate investigations at higher gas pressures. New ways of producing hyperpolarized 3 He for magnetic resonance imaging and medical applications can be envisaged, as most clinical whole-body scanners operate at 1.5 T.
Nuclear polarization through optical pumping of gaseous 3He below 1 K
Journal de Physique Lettres, 1983
2014 La méthode du pompage optique qui permet d'orienter nucléairement 3He gazeux a pu être étendue au domaine des températures en dessous de 1 K. L'utilisation d'un enduit superfluide de 4He couvrant la paroi interne de la cellule a permis de réduire très fortement la relaxation nucléaire intense qui serait produite par du pyrex nu. On obtient ainsi des temps de relaxation nucléaires relativement longs (Tr ~ 103 s), même aux températures les plus basses accessibles dans l'expérience (T ~ 500 mK). Abstract. 2014 We have extended to temperatures below 1 K the optical pumping technique for polarizing the nuclei pf ground state 3He atoms in the gas phase. A superfluid 4He film covering the surface of the pyrex cell protected the 3He atoms from the rapid depolarization processes that would be experienced in the presence of bare pyrex walls. Relatively long relaxation times of order 103 s were observed at temperatures down to 500 mK, the lowest temperature accessible with the present apparatus.
Enhancement of [sup 129]Xe polarization by off-resonant spin exchange optical pumping
Journal of Applied Physics, 2010
A high power narrow line width (38W, 0.09nm FWHM) external cavity diode laser is investigated for rubidium spin exchange optical pumping of 129 Xe. This tunable photon source has a constant line width, independent of operating power or wavelength within a 1 nm tuning range. When using this laser, an increase in the 129 Xe nuclear polarisation is observed when optically pumping at a lower wavelength than the measured Rb electron D 1 absorption. The exact detuning from D 1 for the highest polarisation is dependent upon the gas density. Furthermore, at high power and/or high Rb density, a reduction of the polarisation occurs at the optimum wavelength as previously reported in SEOP studies of 3 He which is consistent with high absorption close to the cell front face. These results are encouraging for moderate high throughput polarisation of 129 Xe in the mid pressure range of (0.5-2.0 amg). * Electronic address: S.R.Parnell@Sheffield.ac.uk † Electronic address: J.M.Wild@Sheffield.ac.uk
Enhancement of 129Xe polarization by off-resonant spin exchange optical pumping
Journal of Applied Physics, 2010
A high power narrow line width (38 W, 0.09 nm full width at half maximum) external cavity diode laser is investigated for rubidium spin exchange optical pumping of X129e. This tunable photon source has a constant line width, independent of operating power or wavelength within a 1 nm tuning range. When using this laser, an increase in the X129e nuclear polarization is observed when optically pumping at a lower wavelength than the measured Rb electron D1 absorption. The exact detuning from D1 for the highest polarization is dependent upon the gas density. Furthermore, at high power and/or high Rb density, a reduction in the polarization occurs at the optimum wavelength as previously reported in spin exchange optical pumping studies of H3e which is consistent with high absorption close to the cell front face. These results are encouraging for moderate high throughput polarization of X129e in the midpressure range of (0.5-2.0 amagat).
Polarized [sup 3]He gas compression system using metastability-exchange optical pumping
Review of Scientific Instruments, 2005
Dense samples (10-100 bar•cm) of nuclear spin polarized 3 He are utilized in high energy physics, neutron scattering, atomic physics, and magnetic resonance imaging. Metastability exchange optical pumping can rapidly produce high 3 He polarizations (≈80%) at low pressures (few mbar). We describe a polarized 3 He gas compressor system which accepts 0.26 bar•l•h −1 of 3 He gas polarized to 70 % by 4 W of Nd:LMA laser power and compresses it into a 5 bar•cm target with final polarization of 55 %. The spin relaxation rates of the system's components have been measured using NMR and a model of the 3 He polarization loss based on the measured relaxation rates and the gas flow is in agreement with a 3 He polarization measurement using neutron transmission.
Hybrid Spin-Exchange Optical Pumping of 3He
Physical Review Letters, 2003
We demonstrate spin-exchange optical pumping of 3 He 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 3 He atoms then transfer the angular momentum to the 3 He with much greater efficiency than Rb-3 He. 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.
Increasing the pump-up rate to polarize 3He gas using spin-exchange optical pumping method
Physica B-condensed Matter, 2009
In recent years, polarized 3 He gas has increasingly been used as neutron polarizers and polarization analyzers. Two of the leading methods to polarize the 3 He 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 3 He 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 3 He to 70% polarization would require 20À40 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 3 He gas using the SEOP method.