Publications HAL de Pierre-Jean, Nacher; P.J., Nacher; P.-J., Nacher, PJ, Nacher; P-J, Nacher; du labo/EPI Laboratoire Kastler Brossel; LKB; Laboratoire de Spectroscopie Hertzienne de l'ENS; UMR 8552; UMR8552;

2023

Conference papers

titre
3He gas diffusion in anisotropic porous media (ordered Al2O3 aerogels)
auteur
Hadi Loutfi, Geneviève Tastevin, Pierre-Jean Nacher, Andrey Stanislavovas, Vyacheslav Kuzmin, Kajum Safiullin, Murat Tagirov
article
Congrès du GERM 2023 "Résonance Magnétique aux Extrêmes", Jun 2023, Murol, France
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https://hal.science/hal-04336800/file/GERM-2023-HL.pdf BibTex

Poster communications

titre
Progress in polarization of 3He atoms in a magnetized plasma (PAMP)
auteur
Alexander Makarchenko, Vyacheslav Kuzmin, Kajum Safiullin, Murat Tagirov, Zeyuan Zhang, Geneviève Tastevin, Pierre-Jean Nacher
article
19th European Magnetic Resonance Meeting (EUROMAR 2023), Jul 2023, Glasgow, United Kingdom. , https://euromar2023.org/wp-content/uploads/2023/07/PA-Book-v3.pdf
resume
Introduction Hyperpolarization techniques allow a strong increase in NMR sensitivity, most often by many orders of magnitude. The recently discovered PAMP technique yields significant 3He polarization at high magnetic field strength, simply obtained by firing a strong rf discharge in the gas [1]. It is a promising alternative to laser-based hyperpolarization in pure helium gas by metastability exchange optical pumping [2]. The physical mechanism of PAMP remains to be firmly established. Aim The reported new investigations aim at further exploration of PAMP dynamics and conditions for improved efficiency, as well as at a deeper insight on the polarization build-up process. Methods 3He gas contained in sealed glass cells [3] of different shapes was polarized in a magnetized plasma from room to 200°C temperature at 3.66 T [4]. Filling pressures lied in the few millibars range and rf powers of up to 60 W were applied to a wired coil to sustain the discharge. Nuclear polarization was monitored by NMR. Simultaneously, the optical fluorescence spectrum of the plasma and the cell temperature were recorded. Results: A set of 3He polarization build-up curves were obtained for a wide range of applied rf power. Correlations between the 3He steady-state polarization values and the atomic oxygen impurity number density and cell temperature measurements were observed. A 3He polarization as high as 8% was reached. Discussion The collected data indicate that higher polarization values should be achievable with higher rf discharge power and gas temperature. Further investigations of PAMP and in-depth studies with complementary diagnostic tools are planned [5]. They will assess the potential of this technique for a variety of NMR-based applications. They will also help for the development of suitable models of PAMP.
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https://hal.science/hal-04334228/file/Euromar2023_PAMP.pdf BibTex
titre
Design of optimal low-frequency NMR detection coils
auteur
Hadi Loutfi, Geneviève Tastevin, Pierre-Jean Nacher
article
European Magnetic Resonance Meeting EUROMAR 2023, Jul 2023, Glasgow (Ecosse), United Kingdom. https://euromar2023.org/abstract-book/
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https://hal.science/hal-04334251/file/Euromar2023_PUCOIL.pdf BibTex
titre
Challenges and solutions for accurate magnetization reversal and tipping outside the RWA
auteur
Geneviève Tastevin, Pierre-Jean Nacher, Christopher P. Bidinosti
article
European Magnetic Resonance Meeting EUROMAR 2023, Jul 2023, Glasgow (Ecosse), United Kingdom. https://euromar2023.org/abstract-book/
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https://hal.science/hal-04334246/file/Euromar2023_Bloch-Siegert.pdf BibTex
titre
Gas diffusion and relaxation within ordered Al2O3 aerogels
auteur
Hadi Loutfi, Geneviève Tastevin, Pierre-Jean Nacher, Andrey Stanislavovas, Vyacheslav Kuzmin, Kajum Safiullin, Murat Tagirov
article
European Magnetic Resonance Meeting EUROMAR 2023, Jul 2023, Glasgow (Ecosse), United Kingdom. https://euromar2023.org/abstract-book/
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https://hal.science/hal-04334265/file/Euromar2023_MARGIN.pdf BibTex

2022

Journal articles

titre
Generating accurate tip angles for NMR outside the rotating-wave approximation
auteur
Christopher P Bidinosti, Geneviève Tastevin, Pierre-Jean Nacher
article
Journal of Magnetic Resonance, 2022, 345, pp.107306. ⟨10.1016/j.jmr.2022.107306⟩
resume
The generation of accurate tip angles is critical for many applications of nuclear magnetic resonance. In low static field, with a linear rather than circular polarized rf field, the rotating-wave approximation may no longer hold and significant deviations from expected trajectories on the Bloch sphere can occur. For rectangular rf pulses, the effects depend strongly on the phase of the rf field and can be further compounded by transients at the start and end of the pulse. The desired terminus can be still be achieved, however, through the application of a phase-dependent Bloch-Siegert shift and appropriate consideration of pulse timings. For suitably shaped rf pulses, the Bloch-Siegert shift is largely phase independent, but its magnitude can vary significantly depending on details of the pulse shape as well as the characteristics of the rf coil circuit. We present numerical simulations and low-field NMR experiments with 1 H and 3 He that demonstrate several main consequences and accompanying strategies that one should consider when wanting to generate accurate tip angles outside the validity of the rotating-wave approximation and in low static field.
DOI
DOI : 10.1016/j.jmr.2022.107306
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https://hal.science/hal-03765938/file/BS_shift-PPwithSM.pdf BibTex

2021

Journal articles

titre
Doppler-free spectroscopy of the lowest triplet states of helium using double optical resonance
auteur
Ali Dia, Marie Abboud, Pierre-Jean Nacher, Geneviève Tastevin
article
The European Physical Journal D : Atomic, molecular, optical and plasma physics, 2021, 75, pp.223. ⟨10.1140/epjd/s10053-021-00233-1⟩
resume
Optical pumping on the 23S-23P transition (1083 nm) of metastable 3He or 4He atoms is used for science and applications. We report on its combination with an optical probe on the 23P{33S transition (706.5 nm) in a ladder-type double optical resonance scheme, with cw single-frequency pump and probe diode lasers. Theoretical expectations for level structure and absorption spectra were computed for both isotopes. Narrow Doppler-free spectral lines were experimentally obtained in low-pressure gas samples. The line weights and their Zeeman structure in weak magnetic field agreed with expectations. The precision of the line positions and line splittings was limited by generic errors of our commercial Fizeau wavemeter, which were independently characterised. The potential of this double resonance scheme for spectroscopic measurements on the three lowest triplet states of He was evaluated. The relevance of velocity- and sublevel-selective pumping combined with polarisation spectroscopy of probe absorption for a study of pressure-dependent population transfers in the 23P state was established.
DOI
DOI : 10.1140/epjd/s10053-021-00233-1
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https://hal.science/hal-03295023/file/706partI-PP.pdf BibTex

Preprints, Working Papers, ...

titre
Magnetic-field coils for metastability-exchange optical pumping, optical spectroscopy, and magnetic resonance of helium
auteur
Pierre-Jean Nacher
article
2021
resume
Optical pumping on the 2$^3$S-2$^3$P transition (1083 nm) of metastable $^3$He or $^4$He atoms is used for science and applications. Gas is usually enclosed in elongated cells with lengths ranging from several centimeters to several meters for efficient absorption, and good magnetic-field homogeneity is needed for reduced diffusion-induced relaxation. We describe a coil system providing a fairly uniform field of arbitrary direction over cell volumes, briefly discuss optimisation parameters and provide example of computed field maps.
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2020

Journal articles

titre
Signal feedback applications in low-field NMR and MRI
auteur
Vyacheslav V Kuzmin, Pierre-Jean Nacher
article
Journal of Magnetic Resonance, 2020, 310, pp.106622. ⟨10.1016/j.jmr.2019.106622⟩
resume
Tuned pick-up coils with high quality factors $Q$ are used in NMR and MRI for high-sensitivity and low-noise detection. However, large $Q$-factors introduce bandwidth issues at low frequency and the associated enhanced currents may cause significant radiation damping effects, especially with hyperpolarised samples. Signal feedback can be used to actively control these currents and adjust the detection bandwidth without resistive losses. Capacitive and inductive coupling methods are compared using detailed models and the operating conditions for efficient feedback with negligible noise penalty are discussed. Several high-impedance commercial preamplifiers have been found to affect the resonance characteristics of tuned coils in a gain-dependent way, or could not be used in low-frequency NMR because of oscillations at large positive gain. This is attributed to an undocumented internal feedback, and could be neutralised using external feedback. The implementation of an inductive coupling scheme to feed a suitably amplified phase-adjusted signal back into the PU coils of low-field NMR systems is described, and three experimental applications are reported. One system is used for NMR studies of distant dipolar field effects in highly polarized liquid $^3$He without or with radiation damping. The moderate intrinsic $Q$-factor ($\approx$7) could be reduced (down to 1) or increased (up to 100) to control transient maser oscillations. Another system was used for MRI of water samples around 2~mT with $Q\approx$190 Litz-wire detection coils. The detection bandwidth was increased by actively reducing the $Q$-factor to obtain uniform sensitivities in images and avoid artifacts introduced by intensity corrections. Finally, parallel acquisition in MRI was performed using two separately tuned detection coils placed above and below the sample. They were actively decoupled using two feedback systems. For an imaging field of view smaller than the sample, artifact-free unfolded images demonstrate the efficiency of this active coil decoupling scheme.
DOI
DOI : 10.1016/j.jmr.2019.106622
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https://hal.science/hal-02069159/file/FB-PP.pdf BibTex

2019

Journal articles

titre
A fast MOSFET rf switch for low-field NMR and MRI
auteur
Pierre-Jean Nacher, Sashika Kumaragamage, Geneviève Tastevin, Christopher P. Bidinosti
article
Journal of Magnetic Resonance, 2019, 310, pp.106638. ⟨10.1016/j.jmr.2019.106638⟩
resume
TRansmit Array Spatial Encoding (TRASE) MRI uses trains of rf pulses alternately produced by distinct transmit coils. Commonly used coil switching involving PIN diodes is too slow for low- and ultra-lowfield MRI and would introduce wait times between pulses typically as long as each individual pulse in a few mT. A MOSFET-based rf switch is described and characterised. Up to hundreds of kHz, it allows for sub-ls switching of rf currents from a single amplifier to several coils with sufficient isolation ratio and negligible delay between pulses. Additionally, current switching at null current and maximum voltage can be used to abruptly stop or start pulses in series-tuned rf coils, therefore avoiding the rise and fall times associated with the Q-factors. RF energy can be efficiently stored in tuning capacitors for times as long as several seconds. Besides TRASE MRI, this energy storage approach may find applications in fast repeated spin-echo experiments. Here, a threefold acceleration of TRASE phase-encoding is demonstrated when MOSFET switches are used instead of fast reed relays.
DOI
DOI : 10.1016/j.jmr.2019.106638
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https://hal.science/hal-02266979/file/switch-PP-v3cor.pdf BibTex

2018

Journal articles

titre
Nuclear hyperpolarization of He3 by magnetized plasmas
auteur
A. Maul, P. Blümler, P.J. Nacher, E. Otten, G. Tastevin, W. Heil
article
Physical Review A : Atomic, molecular, and optical physics [1990-2015], 2018, 98 (6), ⟨10.1103/PhysRevA.98.063405⟩
resume
We describe a method, referred to as PAMP (polarization of atoms in a magnetized plasma), that allows hyperpolarization of 3He nuclear spins at high magnetic field solely by excitation of a rf gas discharge. A magnetized plasma is obtained when the mean free path of the free electrons is much larger than their gyration radius in the rf gas discharge. Investigations of PAMP are carried out in the 1–15-mbar pressure range with rf excitation around 100 MHz. Quantitative NMR measurements at 4.7 T and room temperature show that, for different cell sizes and gas densities, 3He nuclear polarizations in the 1 to 9% range are achieved (i.e., larger than the Boltzmann equilibrium spin polarization of the free electrons). A description involving alignment-to-orientation conversion in the excited 23P state is proposed. The PAMP method appears as a very attractive alternative to established laser polarization techniques (spin exchange or metastability exchange optical pumping). Application to 3He nuclear magnetometry with a relative precision of 10^(−12) is demonstrated.
DOI
DOI : 10.1103/PhysRevA.98.063405
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https://arxiv.org/pdf/1806.07624 BibTex

Conference papers

titre
A Fast MOSFET Switch for RF Pulse Management and Shaping in Low-Field NMR and MRI
auteur
Pierre-Jean Nacher, Sashika Kumaragamage, Geneviève Tastevin, Christopher Bidinosti
article
European Magnetic Resonance Meeting EUROMAR 2018, Jul 2018, Nantes, France
resume
TRansmit Array Spatial Encoding (TRASE) is a MRI method that achieves spatial encoding through repeated pulses of radiofrequency (RF) B1 fields from different phase-gradient transmit coils. It does not require the application of B0 gradients and is a distinct alternative to the standard MRI approach.1 An evaluation of the benefits and limitations of TRASE MRI at low field (a few mT) is under way using hyperpolarised gas samples.2,3 Fast switching between two or more transmit coils with negligible wait time between pulses is required to reduce the total RF encoding time. PIN diodes are often used for coil switching in MRI but bias control with RF isolation involves response times (several RF periods) which are too slow for the targeted low-frequency application. We have designed bidirectional MOSFET switches with floating and optically isolated gate control.4 A similar device was recently reported to be suitable as Q-switch in low-field NMR.5 Our tests have been performed with different RF power amplifiers and different loads at various frequencies (in the DC – 200 kHz range). An Apollo Tecmag console was used to manage RF pulses and TTL signals controlling the switches. RF currents were recorded using a digital oscilloscope by monitoring the voltage drop across a 1-Ω resistor inserted on the ground line at the output of the RF amplifier. Our MOSFET switch (with components rated for 500V and 32 A or for 1.7kV and 9A) has switching times below 1 μs. It has a low ON impedance (R~1 Ω) and a frequency-dependent OFF impedance (~500 pF capacitance), yielding efficient RF current switching in resistive loads and in transmit coils (various situations will be reported). Additionally, current switching at null current and maximum voltage can be used to abruptly stop or start pulses in series-tuned RF coils, therefore avoiding the rise and fall times associated with the Q-factors (Fig. 1). RF energy can be efficiently stored in tuning capacitors for times as long as hundreds of milliseconds. Besides TRASE MRI, this energy storage approach may find applications in fast repeated spin-echo experiments.
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titre
New Insights on Precession Instabilities in Highly Polarized Liquids
auteur
Geneviève Tastevin, Pierre-Jean Nacher, Vjacheslav Kuzmin
article
2018 European Magnetic Resonance Meeting (Euromar 2018), Jul 2018, Nantes, France
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titre
Exploration of TRASE MRI at Low Magnetic Field: Potential Performance and Limitations
auteur
Pierre-Jean Nacher, Geneviève Tastevin, Christopher P. Bidinosti
article
European Magnetic Resonance Meeting EUROMAR 2018, Jul 2018, Nantes, France. pp.574
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titre
Unconventional trajectories on the Bloch Sphere: A closer look at the effects and consequences of the breakdown of the rotating wave approximation
auteur
Christopher B. Bidinosti, Pierre-Jean Nacher, Geneviève Tastevin
article
Joint annual meeting ISMRM-ESMRMB 2018, Proc. of the Intl. Soc. Mag. Reson. Med., Jun 2018, Paris, France. pp.2701
resume
TRASE MRI uses rapid π-pulses of phase gradient fields, and in general requires as many as two distinct phase-gradient coils per encoding direction. This tends to restrict one to large amplitude, linear B1 fields, which in low B0 field leads to a breakdown of the rotating wave approximation. We have studied this regime both numerically and experimentally. Our results show a rich behavior involving a complex interplay of the Bloch-Siegert shift, the B1 start and stop phase, and B1 amplitude transients.
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https://hal.science/hal-02366402/file/Edited%20PDF_Bidinosti%20et%20al_ISMRM2018_BS%20abstract.pdf BibTex
titre
Concomitant B1 Field in Low-Field MRI: Potential Contributions to TRASE Image Artefacts
auteur
Christopher B. Bidinosti, Pierre-Jean Nacher, Geneviève Tastevin
article
Joint annual meeting ISMRM-ESMRMB 2018, Proc. of the Intl. Soc. Mag. Reson. Med., Jun 2018, Paris, France. pp.2670
resume
TRansmit Array Spatial Encoding (TRASE) MRI uses trains of rf pulses produced by transmit coils which generate transverse fields of uniform magnitude and spatially varying directions. These coils also unavoidably generate concomitant rf fields, which in turn affect magnetisation dynamics during rf flips in low-field NMR. Bloch's equation are numerically solved to show that π-pulses imperfectly reverse transverse magnetisation and that the resulting error in azimuthal angle linearly increases with B1/B0, with the number of pulses in the TRASE pulse train, and with distance from the coil axis in the sample. This may induce significant image distortions or artefacts. Supporting experiments performed at 2 mT will be reported.
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https://hal.science/hal-02366411/file/Edited%20PDF_Bidinosti%20et%20al_ISMRM%202018_ConcomitantB1.pdf BibTex

2016

Book sections

titre
History and physical principles of MRI
auteur
Michael E. Hayden, Pierre-Jean Nacher
article
Luca SABA. Magnetic Resonance Imaging Handbook, 1, CRC press, 2016, 978-1482216288
resume
The first chapter of the three-volume Magnetic Resonance Imaging Handbook describes the historical and physical background of modern nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) methods and techniques.
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https://hal.science/hal-01191404/file/Ch1_2col_Final_May24_2015_PPHAL.pdf BibTex

2015

Journal articles

titre
An improved shielded RF transmit coil for low-frequency NMR and MRI
auteur
Viacheslav V. Kuzmin, Christopher P. Bidinosti, Michael E. Hayden, Pierre-Jean Nacher
article
Journal of Magnetic Resonance, 2015, 256, pp.70--76. ⟨10.1016/j.jmr.2015.05.001⟩
resume
We describe an actively shielded cylindrical RF transmit coil producing a highly uniform internal field (±0.5%) over an extended volume and a strongly suppressed (÷20) external field. Direct field mapping and experimental checks using in-situ NMR and MRI of polarised 3 He at low temperature demonstrate performance consistent with numerical field computations.
DOI
DOI : 10.1016/j.jmr.2015.05.001
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https://hal.science/hal-01141760/file/PP_B1coils_2col.pdf BibTex

2013

Journal articles

titre
Metastability exchange optical pumping of 3He gas up to hundreds of millibars at 4.7 Tesla
auteur
A. Nikiel-Osuchowska, Guilhem Collier, Bartosz Glowacz, Tadeusz Palasz, Z. Olejniczak, W. Weglarz, Geneviève Tastevin, Pierre-Jean Nacher, Tomasz Dohnalik
article
The European Physical Journal D : Atomic, molecular, optical and plasma physics, 2013, 67 (9), pp.200. ⟨10.1140/epjd/e2013-40153-y⟩
resume
Metastability exchange optical pumping (MEOP) is experimentally investigated in 3He at 4.7 T, at room temperature and for gas pressures ranging from 1 to 267 mbar. The 23S - 23P transition at 1083 nm is used for optical pumping and for detection of the laser-induced orientation of 3He atoms in the rf discharge plasmas. The collisional broadening rate is measured (12.0 ± 0.4 MHz.mbar-1 FHWM) and taken into account for accurate absorption-based measurements of both nuclear polarization in the ground state and atom number density in the metastable state. The results lay the ground for a comprehensive assessment of the efficiency of this method, by comparison with achievements at lower magnetic field strengths (1 mT - 2 T) over an extended range of operating conditions. Stronger hyperfine decoupling in the optically pumped metastable state is observed to systematically lead to slower build-up of nuclear orientation in the ground state, as expected. The nuclear polarizations obtained at 4.7 T still decrease at high gas pressures but in a less dramatic way than observed at 2 T in the same sealed glass cells. To date, thanks to the linear increase in gas densities, they correspond to the highest nuclear magnetizations achieved by MEOP in pure 3He gas. The improved efficiency puts less demanding requirements for compression stages in polarized gas production systems and makes high-field operation particularly attractive for magnetic resonance imaging of the lungs, for instance.
DOI
DOI : 10.1140/epjd/e2013-40153-y
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https://hal.science/hal-00790331/file/PP-HAL_MEOP_4p7T_final.pdf BibTex
titre
Comment on "Enhanced polarization and mechanisms in optically pumped hyperpolarized 3He in the presence of 4He
auteur
T. R. Gentile, Michael E. Hayden, Pierre-Jean Nacher, A.K. Petukhov, B. Saam, T. G. Walker
article
Physical Review A : Atomic, molecular, and optical physics [1990-2015], 2013, 88, pp.017401. ⟨10.1103/PhysRevA.88.017401⟩
resume
Chen et al. [Phys. Rev. A 81, 033422 (2010)] claim that adding 4He to spin-exchange optical pumping (SEOP) cells confines 3He atoms to a diffusion-limited region, which effectively reduces the wall relaxation factor X. Here X is a phenomenological parameter used to characterize typical SEOP cells; it quantifies the observation that the measured linear slope of the relaxation rate with alkali-metal-atom density exceeds the spin-exchange rate. In addition they claim to demonstrate that magnetic-field gradients cause a diffusive motion of 3He. We argue that these claims and other central conclusions drawn by Chen et al. [ Phys. Rev. A 81, 033422 (2010)] are inconsistent with the physics of diffusion or should not be made from the data as presented. We also draw attention to several additional issues associated with the results, analysis, and presentation of data in Chen et al. [ Phys. Rev. A 81, 033422 (2010)] that confound clear interpretation.
DOI
DOI : 10.1103/PhysRevA.88.017401
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titre
Multiple echoes due to distant dipolar fields in NMR of hyperpolarized noble gas solutions
auteur
Steven W. Morgan, Emmanuel Baudin, Gaspard Huber, Patrick Berthault, Geneviève Tastevin, Maurice Goldman, Pierre-Jean Nacher, Hervé Desvaux
article
The European Physical Journal D : Atomic, molecular, optical and plasma physics, 2013, pp.67:29. ⟨10.1140/epjd/e2012-30470-0⟩
resume
We report on multiple echo measurements in hyperpolarized liquids using optically pumped spin-1/2 noble gas atoms: either129Xe dissolved in cyclohexane or 3He dissolved in superfluid 4He. An NMR pulse sequence 90° -tau -90° (with slice-selective flipping pulses for 129Xe experiments) was used and long echo trains have been observed in the presence of applied gradients due to average dipolar fields typically one order of magnitude larger than those of bulk water in high magnetic fields. We show that a mean field description is valid for explaining the multiple echoes observed in these liquids, even for spin temperatures as low as 10mK for 129Xe or 10µK for 3He, and the echoes originate from the distant dipolar fields within the samples. Numerical lattice simulations have been used to assess the effects of slice selection and of finite sample size in addition to those of atomic diffusion. They account for the observed echo widths and amplitudes much better than previously published models which disregard finite size effects that appear to be of key importance. This opens the way to using multiple echoes resulting from distant dipolar fields for the determination of the absolute magnetization in hyperpolarized liquids without signal calibration.
DOI
DOI : 10.1140/epjd/e2012-30470-0
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https://hal.science/hal-00762884/file/echoes_EPJD_PPv2.pdf BibTex
titre
Achieving high spatial resolution and high SNR in low-field MRI of hyperpolarised gases with Slow Low Angle SHot
auteur
Kayum Safiullin, Cavin Talbot, Pierre-Jean Nacher
article
Journal of Magnetic Resonance, 2013, 227, pp.72-86. ⟨10.1016/j.jmr.2012.11.025⟩
resume
MRI of hyperpolarised gases is usually performed with fast data acquisition to achieve high spatial resolutions despite rapid diffusion-induced signal attenuation. We describe a double-cross k-space sampling scheme suitable for slow low angle shot (SLASH) acquisition and yielding an increased SNR. It consists of a series of anisotropic partial acquisitions with a reduced resolution in the read direction, which alleviates signal attenuation and still provides a high isotropic resolution. The advantages of SLASH imaging over conventional FLASH imaging are evaluated analytically, using numerical lattice calculations, and experimentally in phantom cells filled with hyperpolarised 3He-N2 gas mixtures. Low-field MRI is performed (here 2.7 mT), a necessary condition to obtain long T2* values in lungs for slow acquisition. Two additional benefits of the SLASH scheme over FLASH imaging have been demonstrated: it is less sensitive to the artefacts due to concomitant gradients and it allows measuring apparent diffusion coefficients for an extended range of times.
DOI
DOI : 10.1016/j.jmr.2012.11.025
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https://hal.science/hal-00761896/file/SLASH-PP-JMR-12-74.pdf BibTex

2010

Conference papers

titre
Fundamentals of metastability exchange optical pumping in helium
auteur
Marion Batz, Pierre-Jean Nacher, Geneviève Tastevin
article
JCNS Workshop on Modern Trends in Production and Applications of Polarized 3He, Jul 2010, Ismaning, Germany. pp.012002, ⟨10.1088/1742-6596/294/1/012002⟩
resume
Advances in metastability exchange optical pumping (MEOP) at high laser powers, but also at high gas pressures and high magnetic field strengths, has provided strong motivation for revisiting the understanding of the limitations of this powerful technique. A comprehensive model has been developped for improved description of the combined effects of OP, ME, and relaxation, and of detailed MEOP features observed over the broad range of operating conditions. A brief description is provided, with illustrative comparisons of computed and experimental results. This improved tool is used to explain the excellent photon efficiency of OP obtained at all field strengths. It is combined with an angular momentum budget approach to quantitatively investigate the newly discovered strong OP-enhanced polarisation losses that currently limits MEOP performance.
DOI
DOI : 10.1088/1742-6596/294/1/012002
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https://hal.science/hal-00562617/file/PP_Nacher_Ismaning2010_revised_apr2011.pdf BibTex
titre
An accurate optical technique for measuring the nuclear polarisation of 3He gas
auteur
Cavin Talbot, Marion Batz, Pierre-Jean Nacher, Geneviève Tastevin
article
JCNS Workshop on Modern Trends in Production and Applications of Polarized 3He, Jul 2010, Ismaning, Germany. pp.012008, ⟨10.1088/1742-6596/294/1/012008⟩
resume
In the metastability exchange optical pumping cells of our on-site production unit and of our other experimental set-ups, we use a light absorption technique to measure the 3He nuclear polarisation. It involves weak probe beams at 1083 nm, that are either perpendicular or parallel to the magnetic field and cell axis, with suitable light polarisations. When metastability exchange collisions control the populations of the sublevels in the 23S state, absolute values of the 3He ground state nuclear polarisation are directly inferred from the ratio of the absorption rates measured for these probe beams. Our report focuses on the transverse detection scheme for which this ratio, measured at low magnetic field for sigma and pi light polarisations, hardly depends on gas pressure or the presence of an intense pump beam. This technique has been systematically tested both in pure 3He and isotopic mixtures and it is routinely used for accurate control of the optical pumping efficiency as well as for calibration of the NMR system.
DOI
DOI : 10.1088/1742-6596/294/1/012008
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https://hal.science/hal-00562616/file/PP_Talbot_Ismaning2010_revised.pdf BibTex
titre
An active feedback scheme for low field NMR experiments
auteur
Emmanuel Baudin, Kayum Safiullin, Steven W. Morgan, Pierre-Jean Nacher
article
JCNS Workshop on Modern Trends in Production and Applications of Polarized 3He, Jul 2010, Ismaning, Germany. pp.012009, ⟨10.1088/1742-6596/294/1/012009⟩
resume
In low field nuclear magnetic resonance (NMR) it is desirable to combine proper characteristics of the detection scheme with a good signal to noise ratio. For example, a reduced coupling between the sample and the detection coil is needed for NMR with highly magnetized samples and a large bandwidth is required in magnetic resonance imaging (MRI). We discuss a solution based on a simple active feedback circuit that preserves the signal to noise ratio as opposed to traditional solutions which do not. We give illustrations of its use in experiments on low temperature hyperpolarized liquid 3He-4He mixtures and in hyperpolarized 3He gas MRI.
DOI
DOI : 10.1088/1742-6596/294/1/012009
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https://hal.science/hal-00562609/file/PP_Baudin_Ismaning2010_revised.pdf BibTex

2009

Journal articles

titre
Using a cw 465nm laser to probe metastable He2 molecules
auteur
Geneviève Tastevin, Bartosz Glowacz, Pierre-Jean Nacher
article
Journal of Low Temperature Physics, 2009, pp.Online first. ⟨10.1007/s10909-009-0050-5⟩
resume
A cw 465~nm laser has been built for sensitive detection of helium metastable molecules by resonant absorption on the a3Σu+(v=0)-e3Πg(v=0) transition band. The frequency-mixing radiation is obtained from commercial laser diodes in a periodically-poled KTP non-linear crystal. The 1.3-nm tuning range includes the main rotational lines of 3He2, 4He2, and 3He-4He dimers. Measurements of absolute molecular densities down to a few 109 cm-3 are reported in low pressure (1-400 mbar) room temperature He gas excited by a weak rf discharge. Unsophisticated detection techniques provide signals with good signal-to-noise ratios thanks to the narrow absorption linewidths (a few GHz, due to Doppler and moderate collisional broadenings) in the fully resolved spectrum. Prospects for use or upgrade of this blue laser to probe the broadened and shifted molecular lines in condensed He are discussed.
DOI
DOI : 10.1007/s10909-009-0050-5
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Book sections

titre
Magnetic Resonance Imaging: From Spin Physics to Medical Diagnosis
auteur
Pierre-Jean Nacher
article
B. Duplantier; J.-M. Raimond; V. Rivasseau. The Spin, Birkhäuser Basel, pp.159 - 193, 2009, Progress in Mathematical Physics, vol. 55, 978-3-7643-8799-0. ⟨10.1007/978-3-7643-8799-0_6⟩
resume
Two rather similar historical evolutions are evoked, each one originating in fundamental spin studies by physicists, and ending as magnetic resonance imaging (MRI), a set of invaluable tools for clinical diagnosis in the hands of medical doctors. The first one starts with the early work on nuclear magnetic resonance, the founding stone of the usual proton-based MRI, of which the basic principles are described. The second one starts with the optical pumping developments made to study the effects of spin polarization in various fundamental problems. Its unexpected outcome is a unique imaging modality, also based on MRI, for the study of lung physiology and pathologies.
DOI
DOI : 10.1007/978-3-7643-8799-0_6
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2008

Journal articles

titre
Nonlinear NMR dynamics in hyperpolarized liquid 3He
auteur
Emmanuel Baudin, Michael E. Hayden, Geneviève Tastevin, Pierre-Jean Nacher
article
Comptes Rendus. Chimie, 2008, 11 (4-5), pp.560 - 567. ⟨10.1016/j.crci.2007.07.005⟩
resume
In a highly polarized liquid (laser-polarized 3He-4He mixtures in our experiment), dipolar magnetic interactions within the liquid introduce a significant nonlinear and nonlocal contribution to the Bloch equation that leads to instabilities during NMR evolution. We have launched a study of these instabilities using spin echo techniques. At high magnetizations, a simple 180° rf pulse fails to refocus magnetization, so we use a standard solid-state NMR pulse sequence: the magic sandwich. We report an experimental and numerical investigation of the effect of this sequence on unstable NMR evolution. Using a series of repeated magic sandwich sequences, the transverse magnetization lifetime can be increased by up to three orders of magnitude.
DOI
DOI : 10.1016/j.crci.2007.07.005
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titre
NMR Time Reversal Experiments in Highly Polarised Liquid 3He-4He Mixtures
auteur
Emmanuel Baudin, Michael E. Hayden, Geneviève Tastevin, Pierre-Jean Nacher
article
Journal of Low Temperature Physics, 2008, 150 (3-4), pp.168 - 173. ⟨10.1007/s10909-007-9532-5⟩
resume
Long-range magnetic interactions in highly magnetised liquids (laser-polarised 3He-4He dilute mixtures at 1 K in our experiment) introduce a significant non-linear and non-local contribution to the evolution of nuclear magnetisation that leads to instabilities during free precession. We recently demonstrated that a multi-echo NMR sequence, based on the magic sandwich pulse scheme developed for solid-state NMR, can be used to stabilise the magnetisation against the effect of distant dipolar fields. Here, we report investigations of echo attenuation in an applied field gradient that show the potential of this NMR sequence for spin diffusion measurements at high magnetisation densities.
DOI
DOI : 10.1007/s10909-007-9532-5
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2007

Journal articles

titre
NMR Time Reversal as a Probe of Incipient Turbulent Spin Dynamics
auteur
Michael E. Hayden, Emmanuel Baudin, Geneviève Tastevin, Pierre-Jean Nacher
article
Physical Review Letters, 2007, 99, pp.137602. ⟨10.1103/PhysRevLett.99.137602⟩
resume
We demonstrate time reversal of nuclear spin dynamics in highly magnetized dilute liquid 3He-4He mixtures through effective inversion of long-range dipolar interactions. These experiments, which involve using magic sandwich NMR pulse sequences to generate spin echoes, probe the spatiotemporal development of turbulent spin dynamics and promise to serve as a versatile tool for the study and control of dynamic magnetization instabilities. We also show that a repeated magic sandwich pulse sequence can be used to dynamically stabilize modes of nuclear precession that are otherwise intrinsically unstable. To date, we have extended the effective precession lifetimes of our magnetized samples by more than three orders of magnitude.
DOI
DOI : 10.1103/PhysRevLett.99.137602
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https://hal.science/hal-00177851/file/hayden.pdf BibTex
titre
Optical measurement of He-3 nuclear polarization for metastable exchange optical pumping studies at high magnetic field
auteur
K. Suchanek, M. Suchanek, A. Nikiel, T. Palasz, Marie Abboud, A. Sinatra, Pierre-Jean Nacher, G. Tastevin, Z. Olejniczak, T. Dohnalik
article
The European Physical Journal. Special Topics, 2007, 144, pp.67-74. ⟨10.1140/epjst/e2007-00109-8⟩
resume
An accurate optical method to measure the nuclear polarization of He-3 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 hyper. ne 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 He-3 gas pressure up to 67 mbar.
DOI
DOI : 10.1140/epjst/e2007-00109-8
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titre
Metastability exchange optical pumping of He-3 at high pressure and high magnetic field for medical applications
auteur
A. Nikiel, T. Palasz, M. Suchanek, Marie Abboud, A. Sinatra, Z. Olejniczak, T. Dohnalik, G. Tastevin, Pierre-Jean Nacher
article
The European Physical Journal. Special Topics, 2007, 144, pp.255-263. ⟨10.1140/epjst/e2007-00138-3⟩
resume
Systematic studies of the metastability exchange optical pumping (MEOP) process in He-3 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 pro. le, 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 3He for magnetic resonance imaging and medical applications can be envisaged, as most clinical whole-body scanners operate at 1.5 T.
DOI
DOI : 10.1140/epjst/e2007-00138-3
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2005

Journal articles

titre
Metastability Exchange Optical Pumping of Helium-3 at High Pressures and 1.5 T: Comparison of two Optical Pumping Transitions
auteur
Marie Abboud, Alice Sinatra, Geneviève Tastevin, Pierre-Jean Nacher, Xavier Maître
article
Laser Physics, 2005, 15, 4, pp.475-479
resume
At low magnetic field, metastability exchange optical pumping of helium-3 is known to provide high nuclear polarizations for pressures around 1 mbar. In a recent paper, we demonstrated that operating at 1.5 T can significantly improve the results of metastability exchange optical pumping at high pressures. Here, we compare the performances of two different optical pumping lines at 1.5 T, and show that either the achieved nuclear polarization or the production rate can be optimized.
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titre
NMR measurements of hyperpolarized 3He gas diffusion in high porosity silica aerogels
auteur
Geneviève Tastevin, Pierre-Jean Nacher
article
Journal of Chemical Physics, 2005, 123, pp.064506. ⟨10.1063/1.1997130⟩
resume
Hyperpolarized 3He is used to nondestructively probe by NMR the structure of custom-made and commercial silica aerogels (97% and 98.5% porous). Large spin-echo signals are obtained at room temperature and very low magnetic field (2mT) even with small mounts of gas. Attenuation induced by applied field gradients results from the combined effects of gas diffusion and confinement by the porous medium on atomic motion. Nitrogen is used as a buffer gas to reach equivalent 3He pressures ranging from 5 mbars to 3.5 bars. The observed pressure dependence suggests a non-uniform structure of the aerogels on length scales up to tens of micrometers. A description by broad phenomenological distributions of mean free paths is proposed, and quantitatively discussed by comparison to numerical calculations. The investigated aerogel samples exhibit different effective diffusion characteristics despite comparable nominal porosities.
DOI
DOI : 10.1063/1.1997130
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Preprints, Working Papers, ...

titre
Polarized Helium to Image the Lung
auteur
Michèle Leduc, Pierre-Jean Nacher
article
2005
resume
The main findings of the european PHIL project (Polarised Helium to Image the Lung) are reported. State of the art optical pumping techniques for polarising 3He gas are described. MRI methodological improvements allow dynamical ventilation images with a good resolution, ultimately limited by gas diffusion. Diffusion imaging appears as a robust method of lung diagnosis. A discussion of the potential advantage of low field MRI is presented. Selected PHIL results for emphysema are given, with the perspectives that this joint work opens up for the future of respiratory medicine.
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2004

Journal articles

titre
High nuclear polarization of helium-3 at low and high pressure by metastability exchange optical pumping at 1.5 Tesla
auteur
Marie Abboud, Alice Sinatra, Xavier Maître, Geneviève Tastevin, Pierre-Jean Nacher
article
EPL - Europhysics Letters, 2004, 68, pp.480. ⟨10.1209/epl/i2004-10237-y⟩
resume
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.
DOI
DOI : 10.1209/epl/i2004-10237-y
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titre
A broadband Ytterbium-doped tunable fiber laser for 3He optical pumping at 1083 nm
auteur
Geneviève Tastevin, Sébastien Grot, Emmanuel Courtade, Sylvain Bordais, Pierre-Jean Nacher
article
Applied Physics B - Laser and Optics, 2004, 78 (2), pp.145-156
resume
Large amounts of hyperpolarized 3He gas with high nuclear polarization rates are required for use in neutron spin filters or nuclear magnetic resonance imaging of human lung. Very high efficiency can be obtained by metastability exchange optical pumping using multimode lasers to excite the 23S-23P transition at 1083 nm. Broadband Ytterbium-doped tunable fiber lasers have been designed for that particular application. Different options for the architecture of the fiber oscillator are presented and compared. Emphasis is given to a linear cavity configuration that includes a high reflectivity fiber mirror and a low reflectivity tunable fiber Bragg grating. Optical measurements are performed to finely characterize the spectral behavior of the lasers. Atomic response is also quantitatively probed to assess the optimal design of the oscillator for optical pumping. Multimode operation matching the 2 GHz Doppler-broadened helium resonance line and tunability over more than 200 GHz are demonstrated. Boosting the output of this fiber laser with a Yb-doped fiber power amplifier, all-fiber devices are built to provide robust, high power turn-key sources at 1083 nm for improved production of laser polarized 3He.
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titre
MRI of the lung using hyperpolarized He-3 at very low magnetic field (3 mT)
auteur
Christopher P. Bidinosti, Jamal Choukeife, Geneviève Tastevin, Alexandre Vignaud, Pierre-Jean Nacher
article
Magnetic Resonance Materials in Physics, Biology and Medicine, 2004, 16, pp.255-258
resume
Optical pumping of He-3 produces large (hyper) nuclear-spin polarizations independent of the magnetic resonance imaging (MRI) field strength. This allows lung MRI to be performed at reduced fields with many associated benefits, such as lower tissue susceptibility gradients and decreased power absorption rates. Here we present results of 2D imaging as well as accurate 1D gas diffusion mapping of the human lung using He-3 at very low field (3 mT). Furthermore, measurements of transverse relaxation in zero applied gradient are shown to accurately track pulmonary oxygen partial pressure, opening the way for novel imaging sequences.
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2003

Journal articles

titre
Restricted diffusion of polarised He-3 gas in aerogels
auteur
G. Tastevin, Pierre-Jean Nacher, J. Choukeife
article
Physica B: Condensed Matter, 2003, 329-333, pp.303-304
resume
Polarised He-3 is used to non-destructively probe by NMR the structure of silica aerogels. Using laser optical pumping large spin-echo signals are obtained with small amounts of gas, even at low magnetic field. Attenuation induced by applied field gradients is measured for equivalent He-3 pressures ranging from 5 mbar to 3 bar. Systematic diffusion studies are performed by NMR on custom-made (98% porous) and commercial (97% porous) aerogels used by research groups to study quantum fluids in confined geometries. The observed pressure dependence suggests a non-uniform structure of both aerogel samples on length scales up to tens of microns. (C) 2003 Elsevier Science B.V. All rights reserved.
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titre
Anomalous spin echoes in highly polarised liquid helium mixtures
auteur
G. Tastevin, N. Piegay, F. Marion, Pierre-Jean Nacher
article
Physica B: Condensed Matter, 2003, 329-333, pp.187-188
resume
NMR experiments are performed on laser polarised liquid helium mixtures in low field (2 mT) above 1 K. Concentrations range from 0.5% to 10% and nuclear polarisations up to 0.1. For large magnetisations, following a 90degrees-tau-180degrees RF pulse pair the spin echo signal detected at time 2tau is significantly smaller than expected from attenuation due to diffusion in the applied static field gradient. Unexpected echoes are also observed at times 3tau, 4tau, 5tau, etc. The first feature may be related to other effects of large dipolar fields in bulk samples (dynamic instabilities, altered transverse decay). Numerical simulations on lattices have been performed to quantitatively interpret all spin echo results. (C) 2003 Elsevier Science B.V. All rights reserved.
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titre
In-vivo NMR of hyperpolarized 3He in the human lung at very low magnetic fields
auteur
Christopher B. Bidinosti, J. Choukeife, Pierre-Jean Nacher, Geneviève Tastevin
article
Journal of Magnetic Resonance, 2003, 162, p.122-132
resume
We present NMR measurements of the diffusion of hyperpolarized 3He in the human lung performed at fields much lower than those of conventional MRI scanners. The measurements were made on standing subjects using homebuilt apparatus operating at 3mT. O2-limited transverse relaxation (T2 up to 15-35 s) could be measured in-vivo. Accurate global diffusion measurements have been performed in-vivo and in a plastic bag; the average apparent diffusion coefficient (ADC) in-vivo was 14.2±0.6 mm2/s, whereas the diffusion coefficient in the bag (3He diluted in N2) was 79.5±1 mm2/s. 1D ADC mapping with high SNR (~200- 300) demonstrates the real possibility of performing quality lung imaging at extremely low fields.
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2002

Journal articles

titre
Magnetic field effects on the 1083 nm atomic line of helium
auteur
Emmanuel Courtade, François Marion, Pierre-Jean Nacher, Geneviève Tastevin, K. Kiersnowski, Tomasz Dohnalik
article
The European Physical Journal D : Atomic, molecular, optical and plasma physics, 2002, 21, pp.25-55. ⟨10.1140/epjd/e2002-00176-1⟩
resume
The structure of the excited $2^{3}$S and $2^{3}$P triplet states of $^{3}$He and $^{4}$He in an applied magnetic field B is studied using different approximations of the atomic Hamiltonian. All optical transitions (line positions and intensities) of the 1083 nm $2^{3}$S-$2^{3}$P transition are computed as a function of B. The effect of metastability exchange collisions between atoms in the ground state and in the $2^{3}$S metastable state is studied, and rate equations are derived, for the populations these states in the general case of an isotopic mixture in an arbitrary field B. It is shown that the usual spin-temperature description remains valid. A simple optical pumping model based on these rate equations is used to study the B-dependence of the population couplings which result from the exchange collisions. Simple spectroscopy measurements are performed using a single-frequency laser diode on the 1083 nm transition. The accuracy of frequency scans and of measurements of transition intensities is studied. Systematic experimental verifications are made for B=0 to 1.5 T. Optical pumping effects resulting from hyperfine decoupling in high field are observed to be in good agreement with the predictions of the simple model. Based on adequately chosen absorption measurements at 1083 nm, a general optical method to measure the nuclear polarisation of the atoms in the ground state in an arbitrary field is described. It is demonstrated at $B\sim$0.1 T, a field for which the usual optical methods could not operate.
DOI
DOI : 10.1140/epjd/e2002-00176-1
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titre
CPMG measurements and ultrafast imaging in human lungs with hyperpolarized helium-3 at low field (0.1 T).
auteur
E. Durand, G. Guillot, L. Darrasse, Geneviève Tastevin, A. Vignaud, D. Vattolo, J. Bittoun, Pierre-Jean Nacher
article
Magnetic Resonance in Medicine, 2002, 47 (1), pp.75-81
resume
This work reports the use of single-shot spin echo sequences to achieve in vivo diffusion gas measurements and ultrafast imaging of human lungs, in vivo, with hyperpolarized He-3 at 0.1 T. The observed transverse relaxation time of He-3 lasted up to 10 s, which made it possible to use long Carr-Purcelf-Meiboom-Gill echo trains. Preliminary NMR studies showed that the resolution of lung images acquired with hyperpolarized He-3 and single-shot sequences is limited to about 6 mm because of the diffusion of the gas in applied field gradients. Ultrafast images of human lungs in normal subjects, achieved in less than 0.4 s with the equivalent of only 130 mu mol of fully polarized He-3, are presented. Comparison with other studies shows that there is no SNR penalty by using low fields in the hyperpolarized case. Advantage was taken of the self diffusion-weighting of the rapid acquisition with relaxation enhancement (RARE) sequence to acquire apparent diffusion coefficient (ADC) images of the lungs. Time scales of seconds could be explored for the first time because there is no hindrance from T-2(star) as with the usual approaches. At 0.1 T, 180 degrees RF pulses can be repeated every 10 ms without exceeding specific absorption rate limits, which would not be the case for higher fields. Moreover, at low field, susceptibility-induced phenomena are expected to be milder. This supports the idea that low-field imagers can be used for hyperpolarized noble gas MRI of lungs and may be preferred for ADC measurements. Magn Reson Med 47:75-81, 2002. (C) 2002 Wiley-Liss, Inc.
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Conference papers

titre
Optical pumping of helium-3 at high pressure and magnetic field
auteur
Pierre-Jean Nacher, Emmanuel Courtade, Marie Abboud, Alice Sinatra, Geneviève Tastevin, Tomasz Dohnalik
article
2002, pp.2225-2236
resume
At low magnetic field, the efficiency of metastability-exchange optical pumping of helium-3 is known to be optimal for pressures around 1 mbar. We demonstrate on several examples (up to 32 mbar) that operating in a higher magnetic field (up to 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.
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https://hal.science/hal-00002223/file/Nacher_PAAT02.pdf BibTex

2001

Journal articles

titre
NMR instabilities and spectral clustering in laser-polarized liquid xenon
auteur
Karen L. Sauer, François Marion, Pierre-Jean Nacher, Geneviève Tastevin
article
Physical Review B: Condensed Matter and Materials Physics (1998-2015), 2001, 63, pp.184427
resume
To study how highly magnetized liquids behave in NMR experiments, we have performed low field NMR on laser-polarized liquid 129Xe, with nuclear polarization of up to 6%. Contrary to conventional NMR results, we find that instabilities develop after a large pulse, leading to an unexpectedly abrupt decay of the signal. In contrast, the NMR spectrum after a small pulse collapses to a series of unusually sharp lines (spectral clustering), whose widths correspond to precession lifetimes longer than a half minute. We discuss the key role of long-range dipolar coupling in such spin dynamics.
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https://hal.science/hal-00002995/file/nmrinst.pdf BibTex

2000

Journal articles

titre
Kinetics of helium-3 laser optical pumping
auteur
M. Leduc, Pierre-Jean Nacher, Geneviève Tastevin, Emmanuel Courtade
article
Hyperfine Interactions, 2000, 127 (1-4), pp.443--449
resume
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.
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titre
Spin polarised He-3 gas for NMR imaging
auteur
Pierre-Jean Nacher, Geneviève Tastevin
article
PHYSICA B, 2000, 284-288, pp.2053-2054
resume
Polarised He-3 gas has been used since 1996 to make in vivo lung NMR images of increasing quality. For the methodological studies performed by various groups so far, hyperpolarised (HP) gas is obtained by laser optical pumping. We present examples of HP gas MRI investigations with potential diagnostic applications. We report on our MRI work at low field (0.1 T), which could result in reduced requirements in equipment and He-3 gas. The growing interest in He-3 gas MRI should lead to the development of cost-efficient schemes to produce large amounts of HP gas and to efficiently recycle He-3. Cryogenic techniques have been proposed to polarise or compress 3He gas. Their potential interest is discussed considering recent technical developments. (C) 2000 Elsevier Science B.V. All rights reserved.
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titre
Spectroscopy of the helium 2 3S - 2 3P transition above 0.01 Tesla - Application to optical pumping studies
auteur
K. Kiersnowski, Emmanuel Courtade, F. Marion, Pierre-Jean Nacher, Geneviève Tastevin
article
Hyperfine Interactions, 2000, 127 (1-4), pp.451--454
resume
Optical pumping of helium makes use of the 2 S-3-2 P-3 transition at 1083 nm. We report on a study of this transition in magnetic fields up to 1.5 T. Based on these results, an optical method to measure nuclear polarisation in arbitrary field has been developed. Preliminary results on optical pumping at 0.1 T are presented.
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titre
Spin diffusion measurements in spin-polarised liquid He-3-He-4 mixtures
auteur
N. Piegay, Geneviève Tastevin, Pierre-Jean Nacher
article
Journal of Low Temperature Physics, 2000, 121 (5-6), pp.785-790
resume
We report on investigations of spin diffusion in isotopic helium liquid mixtures using a multi-echo technique in applied magnetic field gradients. Samples (up to 1 cm(3) in volume) are obtained by liquefaction of optically polarised gas. NMR measurements are performed at saturated vapour pressure in a low magnetic field (2.2 mT). Signal-to-noise ratios stay high down to He-3 concentrations of order a few parts per thousand at 1K for instance. We demonstrate that the experimental accuracy of spin diffusion measurements is substantially improved using optically polarised mixtures. We have observed that the dynamics of the precession of the transverse magnetisation can be altered due to large dipolar fields at high magnetisation densities. Effects on spin-echo signals and implications for the extension of spin diffusion measurements with our technique are discussed.
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titre
NMR instabilities in spin-polarised liquids: He-3, He-3-He-4 mixtures and Xe-129
auteur
Pierre-Jean Nacher, Geneviève Tastevin, B. Villard, N. Piegay, K. Sauer
article
Journal of Low Temperature Physics, 2000, 121 (5-6), pp.743-748
resume
We report on pulsed NMR experiments performed in low magnetic field (1-2 mT) on various spin-polarised liquid samples obtained from optically pumped gas. Thin films of pure He-3 and bulk samples of dilute He-3-He-4 mixtures are prepared with polarisations up to 40%. Xenon is liquefied (at 166 K) within a narrow U-shaped tube with polarisations of older 6%. In all these highly magnetised anisotropic samples, dipolar magnetic couplings have a strong influence on spin dynamics. Spect? al clustering is obtained for small tipping angles and usually results in precession lifetimes of several seconds. Much shorter precession lifetimes (down to 10 ms) are obtained for larger tipping angles in highly polarised samples. In all systems, 90 degrees tipping pulses are followed by precession signals which abruptly decay after a variable delay: as long as 1 s for moderate polarisations in xenon. Use of different liquids permits us to vary the effects of dipolar couplings, quantum exchange and spin diffusion, and to probe their influence on the observed phenomena.
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1998

Journal articles

titre
Magnetic resonance imaging using polarized noble gases
auteur
M. Leduc, Pierre-Jean Nacher, G. Tastevin
article
Laser Physics, 1998, 8 (3), pp.799--802
resume
A new technique of medical imaging based on NMR has been developed, making use of spin polarized gases, He-3 or Xe-129, introduced inside the human body, where the polarization lives long enough to allow images to be taken. 3D images have been recorded for the lungs of living animals and humans with a resolution of a few mm(3). The polarization methods are based on optical pumping, for which we discuss the possible improvements in the technology of the required cw infrared lasers. We also display the advantages opened up by MRT in low magnetic field. Finally we comment on the perspectives of this MRI method in the field of medicine and biophysics, especially in functional ventilation and perfusion imaging.
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1997

Journal articles

titre
1083 nm ytterbium doped fibre amplifier for optical pumping of helium
auteur
S. V. Chernikov, J. R. Taylor, N. S. Platonov, V. P. Gapontsev, Pierre-Jean Nacher, G. Tastevin, M. Leduc, M. J. Barlow
article
Electronics Letters, 1997, 33 (9), pp.787--789
resume
A combination of a narrow linewidth, tunable DBR diode laser and high power ytterbium fibre amplifier in a master oscillator power fibre amplifier (MOPFA) configuration is demonstrated for efficient optical pumping of helium. A compact and efficient diode pumped prototype system is shown to compare favourably with alternative laser sources for production of hyperpolarised He-3 using direct pumping for medical application in MRI.
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titre
MRI of hyperpolarized gases in competition with nuclear medicine?
auteur
Pierre-Jean Nacher, Geneviève Tastevin, A. Constantinesco, P. Choquet, M. Wioland, M. Leduc
article
Medecine Nucleaire: Imagerie Fonctionnelle Et Metabolique, 1997, 21 (5), pp.285--292
resume
Optical pumping techniques with laserlight were recently used to polarize the nuclear spins of gaseous xenon and helium in order to achieve magnetic resonance imaging of ventilatory lung spaces. Due to their properties, hyperpolarized noble gases open new windows in functional ventilation and perfusion imaging. This article presents the state of the art of these techniques and discusses their perspectives with respect to standard nuclear medicine methods.
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titre
Low-field He-3 nuclear magnetic resonance in human lungs
auteur
L. Darrasse, G. Guillot, Pierre-Jean Nacher, G. Tastevin
article
Comptes rendus de l’Académie des sciences. Série 2, 1997, 324 (11), pp.691--700
resume
We report the first in vivo NMR experiments performed with hyperpolarised He-3 gas at 0.1 T. Hyperpolarisation is achieved by laser optical pumping of He-3 atoms in the metastable triplet state. Longitudinal relaxation times of nuclear magnetisation of the order of 35 s are measured in human lungs. Very long transverse relaxation times of a few seconds are also observed. This work establishes the possibility of magnetic resonance imaging of human lung airways at low field.
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1996

Journal articles

titre
Study of moderately concentrated spin-polarized He-3-He-4 mixtures above TF
auteur
G. Tastevin, B. Villard, Pierre-Jean Nacher
article
Czechoslovak Journal of Physics, 1996, 46, pp.237-238
resume
Laser optical pumping in low magnetic field provides high nuclear polarizations in gaseous helium mixtures, which are liquefied without substantial loss of spin orientation. Polarized liquid mixtures with He-3 concentrations from 0.05 to 0.30 have been studied between 0.5 and 2.4 K. Coating the inner surface of the glass sample container with cesium strongly reduces wall relaxation, so that bulk longitudinal relaxation times could be measured. Evaporation of polarized liquid samples allowed to retrieve large amounts of high pressure spin polarized room temperature gas into a detachable storage cell.
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titre
High nuclear polarization in He-3 and He-3-He-4 gas mixtures by optical pumping with a laser diode
auteur
E. Stolz, M. Meyerhoff, N. Bigelow, M. Leduc, Pierre-Jean Nacher, G. Tastevin
article
Applied Physics B - Laser and Optics, 1996, 63 (6), pp.629--633
resume
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 a He-3 gas up to M = 50% over the pressure range 0.4-1.6 torr. Larger nuclear polarizations M of He-3 nuclei, of order 80%, can be obtained in He-3-He-4 mixtures when the laser frequency is tuned to a He-4 line. A standard optical measurement of nuclear polarization M has been extended to the case of He-3-He-4 mixtures. The effect of various parameters on the steady-state polarization M and on the pumping time T-p is discussed.
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titre
Recent results on hyperpolarized He-3-He-4 liquid mixtures
auteur
Pierre-Jean Nacher, E. Stoltz, G. Tastevin
article
Czechoslovak Journal of Physics, 1996, 46 (Supplement 6), pp.3025-3032
resume
Laser optical pumping in law magnetic field provides very high nuclear polarizations in gaseous helium mixtures, and is used to prepare polarized liquid. Wall relaxation in glass cells is efficiently reduced using cesium coatings, and bulk longitudinal relaxation times are measured. In highly magnetized samples, dipolar fields control the spin dynamics in anisotropic volumes and weak external magnetic field inhomogeneities. Long lived magnetostatic modes are observed by pulsed NMR. Detailed analysis of their frequency and damping gives information on magnetization density and spin diffusion coefficient in polarized mixtures. Experiments are performed above 0.2 K on mixtures with He-3 concentrations of order a few percents or larger. When phase separation occurs, the He-3-rich phase retains a high polarization.
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1991

Journal articles

titre
Experimental evidence for nonwetting with superfluid helium
auteur
P.J. Nacher, J. Dupont-Roc
article
Physical Review Letters, 1991, 67 (21), pp.2966-2969
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titre
Kinetic theory for quantum gases
auteur
Geneviève Tastevin, Pierre-Jean Nacher, Franck Laloë
article
Annalen der Physik, 1991, 48, pp.149
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titre
A Kinetic Equation for Quantum Gases
auteur
Pierre-Jean Nacher, G. Tastevin, F. Laloë
article
Annalen der Physik, 1991, 48 (1-3), pp.149--168
resume
We apply the formalism of the free Wigner transform to the derivation of a kinetic equation valid for dilute quantum gases; this formalism is compatible with a precise treatment of two-body correlations and allows the inclusion of second virial corrections. We generalize the results obtained in previous articles where the calculation of the collision integral was limited to zero ("local") and first order gradient terms; here we use a more general ("non-local") form for the interaction term which is an integral of higher dimension (18). The conservation laws are studied in this formalism, which implies non-linear expressions for the local hydrodynamic quantities in terms of the function appearing in the kinetic equation. The pressure at thermal equilibrium is then evaluated and found to be equal to the value predicted by the Beth-Uhlenbeck formula, without adjusting any free parameter of the theory.
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1990

Journal articles

titre
Heat Conduction in Spin-Polarized Gaseous He-3 at Low Temperature
auteur
C. Larat, M. Leduc, Pierre-Jean Nacher, G. Tastevin, G. Vermeulen
article
Journal of Low Temperature Physics, 1990, 80 (5-6), pp.299--314
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1989

Journal articles

titre
Une équation cinétique pour les gaz quantiques
auteur
Geneviève Tastevin, Pierre-Jean Nacher, Franck Laloë
article
Journal de Physique, 1989, 50, pp.1879
resume
This article is the second of a series where we propose a theory of the dynamics of quantum gases with a precise treatment of the short range two body correlations. For this purpose, we use a variant of the Wigner transform, the "free transform" , which has a useful property in this context: if, before collision, two particles are uncorrelated, the incoming part of the free Wigner transform remains always exactly factorized. Therefore, instead of asssuming a factorization of the two particle distribution, it is less restrictive to make a similar assumption on the free transform. Time symmetry is broken when the correlations of the outgoing part of the free transform are ignored; this approximation, which is well in the spirit of Boltzmann, amounts to considering successive collisions as independent processes (the correlations present in the outgoing part could play a role if the same particles rapidly collided again, an unlikely event in dilute gases). Therefore, the succession of collisions is not treated exactly, but each collision is, even during interaction. One then obtains a closed set of equations which leads directly to a kinetic equation for the free distribution $ f $. The equation includes retardation and quantum refraction effects, and provides a generalization of the Boltzmann equation. The reconstruction of the two particle distribution function $ f_{II} $ from $ f $ reintroduces the effects of short range correlations and, more generally, gives the values of all one particle and two particle physical observables. The price to pay for not using the usual one particle distribution is that the relation between the local physical quantities (density of particles, energy density, etc.) becomes more complicated than in the usual theory, and includes terms which are non linear in $ f $. We nevertheless show how this formalism automatically satisfies the local conservation of all hydrodynamic quantities: particle, momentum and energy densities. The pressure tensor includes quadratic terms which correspond to second virial corrections. The temperature of the gas is defined from the kinetic energy of the particles when they are far apart from each other. We finally briefly discuss the connections of this formalism with the classical Enskog theory, or mean field type theories such as the Landau theory (in particular, we note the presence of recoil effects in the "molecular field")
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https://hal.science/hal-00001438/file/WIGNER-2.pdf BibTex
titre
Dynamique des gaz quantiques (particules discernables sans spin)
auteur
Pierre-Jean Nacher, Geneviève Tastevin, Franck Laloë
article
Journal de Physique, 1989, 50, pp.1907
resume
Nous appliquons les résultats de deux articles précédents, en particulier uneéquation cinétique généralisant l'équation de Boltzmann, à l'étude des gaz dilués quantiques hors d'équilibre. Par une simple extension de la méthode de Chapman Enskog appliquée à cette équation cinétique, nous calculons les propriétés hydrodynamiques du gaz. A l'ordre le plus bas (hydrodynamique d'Euler), nous obtenons des résultats pour la pression, la vitesse du son et la capacité calorifique qui, contrairement à ceux de la théorie de Boltzmann, contiennent les secondes corrections du viriel. A l'ordre suivant (hydrodynamique visqueuse, ou de Navier Stokes), nous obtenons les corrections du premier ordre en densité aux coefficients de transport, et montrons qu'il peut exister un terme de seconde viscosité, quadratique en densité. Ce formalisme donne accès aux parties des corrections du viriel des coefficients de transport qui dépendent des collisions à deux corps, mais pas à celles qui sont dues aux collisions ternaires. Il est quantique et permet de réobtenir l'expression de Beth et Uhlenbeck de la seconde correction du viriel en fonction des déphasages.
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https://hal.science/hal-00001436/file/WIGNER-3.pdf BibTex
titre
Dynamique des gaz quantiques (particules discernables sans spin)
auteur
P.J. Nacher, G. Tastevin, F. Laloë
article
Journal de Physique, 1989, 50 (14), pp.1907-1941. ⟨10.1051/jphys:0198900500140190700⟩
resume
Nous appliquons les résultats de deux articles précédents, en particulier une équation cinétique généralisant l'équation de Boltzmann, à l'étude des gaz dilués quantiques hors d'équilibre. Par une simple extension de la méthode de Chapman Enskog appliquée à cette équation cinétique, nous calculons les propriétés hydrodynamiques du gaz. A l'ordre le plus bas (hydrodynamique d'Euler), nous obtenons des résultats pour la pression, la vitesse du son et la capacité calorifique qui, contrairement à ceux de la théorie de Boltzmann, contiennent les secondes corrections du viriel. A l'ordre suivant (hydrodynamique visqueuse, ou de Navier Stokes), nous obtenons les corrections du premier ordre en densité aux coefficients de transport, et montrons qu'il peut exister un terme de seconde viscosité, quadratique en densité. Ce formalisme donne accès aux parties des corrections du viriel des coefficients de transport qui dépendent des collisions à deux corps, mais pas à celles qui sont dues aux collisions ternaires. Il est quantique et permet de réobtenir l'expression de Beth et Uhlenbeck de la seconde correction du viriel en fonction des déphasages.
DOI
DOI : 10.1051/jphys:0198900500140190700
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https://hal.science/jpa-00211037/file/ajp-jphys_1989_50_14_1907_0.pdf BibTex
titre
Dynamics of Quantum Gases (Distinguishable Particles without Spin)
auteur
Pierre-Jean Nacher, G. Tastevin, F. Laloe
article
Journal de Physique, 1989, 50 (14), pp.1907--1941
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Conference papers

titre
Kinetic theory of quantum gases: beyond the Boltzmann equation
auteur
Geneviève Tastevin, Pierre-Jean Nacher, Franck Laloë
article
SPOQS III, 1989, Torino, Italy. pp.310
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1988

Journal articles

titre
Obtaining polarized liquid helium 3 from optically oriented gas
auteur
G. Tastevin, P.J. Nacher, L. Wiesenfeld, M. Leduc, F. Laloë
article
Journal de Physique, 1988, 49 (1), pp.1-6. ⟨10.1051/jphys:019880049010100⟩
resume
Spin polarized liquid helium three can be obtained by liquefaction of a gas polarized by laser optical pumping. We show that this method can lead to nuclear polarizations exceeding 40 % in a liquid at about 400 mK and almost zero pressure. The relaxation time of the orientation is a few minutes, comparable to the relaxation time of weakly polarized bulk liquid. The NMR signals given by the liquid are strongly shifted in frequency ; this provides a precise and convenient way to measure the polarization and to follow the motion of the liquid inside the experimental cell.
DOI
DOI : 10.1051/jphys:019880049010100
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https://hal.science/jpa-00210670/file/ajp-jphys_1988_49_1_1_0.pdf BibTex
titre
Non-Magnetic Metal and Glass He-3 Cryostat Immersed in a 4.2 K Bath
auteur
Pierre-Jean Nacher, G. Tastevin, L. Wiesenfeld
article
Review of Scientific Instruments, 1988, 59 (2), pp.304--306
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titre
Obtaining polarized liquid 3He from optically oriented gas
auteur
Geneviève Tastevin, Pierre-Jean Nacher, Laurent Wiesenfeld, Michèle Leduc, Franck Laloë
article
Journal de Physique, 1988, 49, pp.1
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1987

Journal articles

titre
Spin-polarized 3He : liquid gas equilibrium
auteur
S. Stringari, M. Barranco, A. Polls, P.J. Nacher, F. Laloë
article
Journal de Physique, 1987, 48 (8), pp.1337-1350. ⟨10.1051/jphys:019870048080133700⟩
resume
We study the effects of nuclear polarization M on the liquid-gas equilibrium phase diagram of 3He, in situations where the saturating vapour pressure increases or decreases as a function of M, and where a metamagnetic instability may occur in the liquid phase. Numerical predictions are given within the frame of a phenomenological model with parameters fitted to reproduce accurately the saturating vapour pressure of the unpolarized liquid as well as its magnetic susceptibility. At temperatures of the order of 0.5 K situations are found where interesting phenomena such as liquid overpolarization and metamagnetic plateaus occur.
DOI
DOI : 10.1051/jphys:019870048080133700
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https://hal.science/jpa-00210560/file/ajp-jphys_1987_48_8_1337_0.pdf BibTex
titre
Heat Conduction Changes in Spin-Polarized Gaseous He-3
auteur
M. Leduc, Pierre-Jean Nacher, D. S. Betts, J.M. Daniels, F. Laloe
article
Japanese Journal of Applied Physics, 1987, 26, pp.213--214
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titre
Nuclear Polarization and Heat Conduction Changes in Gaseous He-3
auteur
M. Leduc, Pierre-Jean Nacher, D. S. Betts, J.M. Daniels, F. Laloe
article
EPL - Europhysics Letters, 1987, 4 (1), pp.59--64
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titre
Spin polarized 3He: liquid gas equilibrium
auteur
Sandro Stringari, Manuel Barranco, A. Polls, Pierre-Jean Nacher, Franck Laloë
article
Journal de Physique Colloque, 1987, C2, pp.101
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titre
Liquefaction of Highly Polarized He-3
auteur
Pierre-Jean Nacher, M. Leduc, G. Tastevin, L. Wiesenfeld
article
Japanese Journal of Applied Physics, 1987, 26, pp.205--206
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titre
Spin polarized 3He: liquid gas equilibrium
auteur
Sandro Stringari, Manuel Barranco, A. Polls, Pierre-Jean Nacher, Franck Laloë
article
Journal de Physique, 1987, 48, pp.1337
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titre
Nuclear polarization and heat conduction changes in gaseous 3He
auteur
Michèle Leduc, Pierre-Jean Nacher, David Betts, James M. Daniels, Geneviève Tastevin, Franck Laloë
article
EPL - Europhysics Letters, 1987, 4, pp.59
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1986

Journal articles

titre
Quantum Properties of Spin-Polarized He-3 Optically Oriented by a LNA Laser
auteur
M. Leduc, F. Laloe, Pierre-Jean Nacher, G. Tastevin, J. M. Daniels, D. Betts
article
Journal of the Optical Society of America B, 1986, 3 (8), pp.P138--P140
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Conference papers

titre
Infrared tunable lasers for helium three optical pumping
auteur
Franck Laloë, Michèle Leduc, James M. Daniels, Pierre-Jean Nacher
article
Montana workshop on Polarized targets and beam sources, 1986, United States
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1985

Journal articles

titre
Direct detection of spin waves in gaseous 3He↑
auteur
G. Tastevin, P.J. Nacher, M. Leduc, F. Laloë
article
Journal de Physique Lettres, 1985, 46 (6), pp.249-254. ⟨10.1051/jphyslet:01985004606024900⟩
resume
In gaseous spin-polarized 3He at low temperature, spin-diffusion becomes oscillatory and gives rise to spin waves; these waves have a quality factor μM, where M is the (relative) nuclear magnetization and μ a dimensionless coefficient characteristic of the importance of exchange effects in binary collisions. We describe here an NMR technique where these oscillatory modes are directly excited and detected, with the use of two sets of radiofrequency coils (for induction and detection), each connected in opposition in order to create or detect pure magnetization gradients over the sample. The measurements of μ are in good agreement with theory as well as with previous experiments, but only at temperatures above 2 K; below, the measurements are affected by processes which are not fully understood, probably related to the formation of a 3He monolayer on the surface of the coating of solid hydrogen which covers the inner surface of the cell.
DOI
DOI : 10.1051/jphyslet:01985004606024900
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https://hal.science/jpa-00232507/file/ajp-jphyslet_1985_46_6_249_0.pdf BibTex
titre
Relaxation nucléaire de 3He gazeux sur H2 solide
auteur
V. Lefèvre-Seguin, P.J. Nacher, J. Brossel, W.N. Hardy, F. Laloë
article
Journal de Physique, 1985, 46 (7), pp.1145-1172. ⟨10.1051/jphys:019850046070114500⟩
resume
Cet article présente une étude expérimentale détaillée de la relaxation-paroi sur des surfaces de H2 solide d'un gaz dilué de 3He, orienté par pompage optique. La grandeur mesurée dans ces expériences est le temps de relaxation global T1 de l'orientation nucléaire de l'échantillon de 3He, lié directement au temps de relaxation Ta de la phase adsorbée (composée d'atomes de 3He adsorbés à la surface de H2 solide). L'étude des variations de T1 en fonction de la température permet de déterminer expérimentalement l'énergie d'adsorption d'un atome de 3He sur H2 solide : ΔW (3He/H2) = 12 ± 3 K. Des expériences complémentaires sur D2 et Ne solides sont également présentées qui conduisent à une mesure de ΔW (3He/D2) = 20 ± 3 K et ΔW (3He/Ne) = 38 ± 5 K, l'ensemble de ces valeurs expérimentales concordant bien avec les prédictions théoriques existantes.
DOI
DOI : 10.1051/jphys:019850046070114500
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https://hal.science/jpa-00210057/file/ajp-jphys_1985_46_7_1145_0.pdf BibTex
titre
Optical pumping of 3He nuclei
auteur
Franck Laloë, Michèle Leduc, Pierre-Jean Nacher, Leonid Novikov
article
Uspehi Fiziceskih Nauk, 1985, 147, pp.433
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Theses

titre
Observations d'ondes de spin dans un gaz d'hélium-3 polarisé par pompage optique laser
auteur
Pierre-Jean Nacher
article
Physique Atomique [physics.atom-ph]. Université Pierre et Marie Curie - Paris VI, 1985. Français. ⟨NNT : ⟩
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https://theses.hal.science/tel-00011855/file/1985NACHER.pdf BibTex

1984

Journal articles

titre
Nuclear Polarization in Gaseous 3He by Optical Pumping
auteur
Michèle Leduc, Stuart B Crampton, Pierre-Jean Nacher, Franck Laloë
article
Nuclear Science Applications A, 1984, 2, pp.1--20
resume
Optical pumping can provide significant nuclear polarizations in gaseous 3He. This method, developed by Colegrove, Schearer and Walters 20 years ago, can be applied to the realization of polarized targets for nuclear physics or neutron spin state filters. Moreover, highly polarized discharges in gaseous helium can be used as sources of polarized beams of atomic or molecular ions or electrons. Some progress has been made recently to obtain higher nuclear polarizations in gaseous 3He at a higher density. Laser optical pumping can produce polarizations over 60% or more in a gas at room temperature. This can be combined with a polarization transfer technique, in which a laser is used to pump 3He in a cell at room temperature, while another cell at a few degrees Kelvin is polarized by diffusion of the atoms through a long connecting tube. Cryogenic coatings, made of solid hydrogen frozen on the coldest parts of the inside wall of the container, reduce very effectively the fast nuclear relaxation which would occur on bare pyrex walls at low temperatures. Nuclear polarizations of the order of 50% have been obtained in a relatively dense gas (n ~ 10^18 cm-3) at T <= 4 K. Higher densities should be attainable by optical pumping at higher gas pressures and, possibly, by subsequent compression of the gas at low temperature.
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https://hal.science/hal-01383488/file/Crampton_NuclSciAppl84_compact.pdf BibTex
titre
Spin rotation effects and spin waves in gaseous 3He↑
auteur
P.J. Nacher, G. Tastevin, M. Leduc, S.B. Crampton, F. Laloë
article
Journal de Physique Lettres, 1984, 45 (9), pp.441-448. ⟨10.1051/jphyslet:01984004509044100⟩
resume
Spin polarized gases such as H↑ or 3He↑ can propagate damped spin waves at low temperatures; their origin is the so-called « identical spin rotation effect » in collisions between identical particles. We report here the observation of such effects in 3He↑ in the temperature range 2 < T < 6 K, and preliminary measurements of the coefficient μ which characterizes the quality factor of the spin oscillations. The measurements are in agreement with the numerical calculations of C. Lhuillier.
DOI
DOI : 10.1051/jphyslet:01984004509044100
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https://hal.science/jpa-00232367/file/ajp-jphyslet_1984_45_9_441_0.pdf BibTex

Conference papers

titre
Laser optical pumping of 3He
auteur
Franck Laloë, Pierre-Jean Nacher, Michèle Leduc, Laird D. Schearer
article
Workshop on polarized 3He beams and targets for nuclear physics, 1984, Princeton, United States
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titre
Nuclear polarization of 3He gas at and below 4.2K by room temperature laser optical pumping
auteur
Michèle Leduc, Stuart B. Crampton, Pierre-Jean Nacher, Franck Laloë
article
SANIBEL Conference and TRIUMF meeting, 1984, Vancouver, Canada
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titre
Observation of spin waves in gaseous 3He
auteur
Pierre-Jean Nacher, Geneviève Tastevin, Michèle Leduc, Stuart B. Crampton, Franck Laloë
article
LT 17, 1984, Karlsruhe, Germany
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1983

Journal articles

titre
Nuclear polarization through optical pumping of gaseous 3He below 1 K
auteur
M. E. Himbert, V. Lefevre-Seguin, P.J. Nacher, J. Dupont-Roc, M. Leduc, F. Laloë
article
Journal de Physique Lettres, 1983, 44 (13), pp.523-529. ⟨10.1051/jphyslet:019830044013052300⟩
resume
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.
DOI
DOI : 10.1051/jphyslet:019830044013052300
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https://hal.science/jpa-00232226/file/ajp-jphyslet_1983_44_13_523_0.pdf BibTex

1982

Journal articles

titre
Relaxation nucléaire de 3He ↑ dans un champ magnétique inhomogène
auteur
V. Lefevre-Seguin, P.J. Nacher, F. Laloë
article
Journal de Physique, 1982, 43 (5), pp.737-753. ⟨10.1051/jphys:01982004305073700⟩
resume
On présente dans cet article une étude théorique de la relaxation de spin d'un gaz atomique dilué, produite par un gradient de champ magnétique de faible intensité. La théorie est valide à la fois en champ faible ou modéré (cas où le temps de corrélation du gaz qui joue un rôle est le temps de diffusion dans son récipient) et en champ fort (c'est alors le temps entre collisions qui joue le rôle essentiel). Elle tient compte des effets quantiques d'indiscernabilité des atomes. Si les effets de divergence du libre parcours moyen dans un gaz polarisé à température nulle ne jouent ici aucun rôle, contrairement à ce qui se produit pour la viscosité par exemple, les effets de « rotation des spins identiques » peuvent être importants.
DOI
DOI : 10.1051/jphys:01982004305073700
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https://hal.science/jpa-00209446/file/ajp-jphys_1982_43_5_737_0.pdf BibTex
titre
Le second coefficient du viriel de H atomique ; effet des variables internes
auteur
V. Lefèvre-Seguin, P.J. Nacher, C. Lhuillier, F. Laloë
article
Journal de Physique, 1982, 43 (8), pp.1199-1211. ⟨10.1051/jphys:019820043080119900⟩
resume
On considère un gaz d'atomes d'hydrogène supposé stable (pas de recombinaison moléculaire), dont les variables internes de spins électronique et nucléaire sont décrites par un opérateur densité fixé ρSI. Les atomes étant chacun constitué d'une paire de fermions (un proton et un électron), non indissociable du fait de l'existence des collisions d'échange de spin, leur comportement de bosons n'est pas évident. Le but de cet article est de discuter dans quelle mesure la pression du gaz est effectivement celle d'un gaz de bosons indissociables, dans le cadre d'un calcul limité à celui du second coefficient du viriel (correction du second ordre en densité pour un gaz dilué). On trouve que ce coefficient comprend en fait plusieurs termes, soit de statistique pure (effets d'indiscernabilité en l'absence d'interaction entre atomes), soit d'interaction et de statistique combinées (effets des potentiels Vg et Vu). Tous ces termes dépendent explicitement des valeurs moyennes d'un certain nombre d'opérateurs de spin, calculables à partir de ρSI. Le terme de statistique pure, dominant à très basse température, correspond à l'échange d'atomes complets (échange simultané de leurs protons et de leurs électrons), ce qui explique son caractère bosonique. En revanche, dans les termes liés aux interactions apparaissent, non seulement des contributions provenant de l'échange d'atomes complets, mais également des contributions liées à l'échange d'un type de particule seulement (protons ou électrons) qu'on peut relier aux effets des collisions d'échange de spin.
DOI
DOI : 10.1051/jphys:019820043080119900
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https://hal.science/jpa-00209497/file/ajp-jphys_1982_43_8_1199_0.pdf BibTex
titre
Polarisation nucléaire de 3He gazeux par pompage optique laser
auteur
P.J. Nacher, M. Leduc, Gérard Trénec, F. Laloë
article
Journal de Physique Lettres, 1982, 43 (15), pp.525-529. ⟨10.1051/jphyslet:019820043015052500⟩
resume
Une polarisation nucléaire élevée, de l'ordre de 70 %, a été obtenue par pompage optique dans 3He gazeux grâce à l'utilisation d'un laser à centres colorés (F+2* dans NaF) fournissant plusieurs centaines de milliwatts à la longueur d'onde λ = 1,08 μm.
DOI
DOI : 10.1051/jphyslet:019820043015052500
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https://hal.science/jpa-00232087/file/ajp-jphyslet_1982_43_15_525_0.pdf BibTex