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Nacher, Pierre-Jean; Piegay, N.; Marion, François; Tastevin, Geneviève

doi:10.1023/a:1013787405665

Cited by 13 publications

(17 citation statements)

References 12 publications

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“…Mono-exponential decays of the echo amplitudes are observed. At high magnetisations (traces b and d), the echo shapes are strongly altered and the much faster decay is no longer exponential, as previously reported [5,10]. Since 180…”

Section: Echo Trains and Diffusion-induced Attenuationsupporting

confidence: 75%

NMR Time Reversal Experiments in Highly Polarised Liquid 3He-4He Mixtures

et al. 2007

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Long-range magnetic interactions in highly magnetised liquids (laser-polarised 3 He-4 He 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.

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Section: Echo Trains and Diffusion-induced Attenuationsupporting

confidence: 75%

NMR Time Reversal Experiments in Highly Polarised Liquid 3He-4He Mixtures

et al. 2007

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“…Similar experiments performed over a range of initial conditions indicate that the characteristic time scale for the abrupt decrease in signal amplitude (i.e. T 1/2 ) is inversely proportional to B dip [21].…”

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confidence: 59%

“…This behavior is expected for an infinite spin system dominated by distant dipolar interactions [6], and has been interpreted as the onset of spin turbulence [3]. We have performed exact numerical simulations of these experiments for small numbers of dipolar-coupled spins diffusing on a cubic lattice (up to 32 × 32 × 32 sites) with periodic boundary conditions [21], and observe excellent agreement between measured and calculated growth rates. In both cases Γ/F dip ∼ 2.3, which is somewhat smaller than the value 2 √ 2π/3 ∼ 3.0 predicted for an infinite spin system [6].…”

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confidence: 62%

NMR Time Reversal as a Probe of Incipient Turbulent Spin Dynamics

et al. 2007

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We demonstrate time reversal of nuclear spin dynamics in highly magnetized dilute liquid 3 He-4 He 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. Elementary treatments of nuclear magnetic resonance (NMR) ignore collective effects. Individual spin dynamics are assumed to be independent of the sample magnetization M, and are thus governed by linear differential equations. This approximation is justified for many -but certainly not all -practical applications. One of the most well known and pervasive counter examples is the phenomenon of radiation damping [1], in which the emf induced in the pickup coil by M drives a current; the magnetic field associated with this current in turn acts on M, driving it into alignment with the static field B 0 in a nonlinear manner. A less common but more insidious problem arises when the magnetic field produced by the magnetized sample becomes large enough to directly influence spin dynamics [2,3,4,5,6]. This leads to a rich variety of nonlinear effects that range from spectral clustering to precession instabilities and spin turbulence. The former arises when small-angle NMR tipping pulses are applied to the sample (generating small angular displacements of M from B 0 ), and is manifest by the spontaneous appearance of long-lived geometrydependent modes of coherent nuclear precession. The latter occurs when large-angle tipping pulses are employed, and involves an exponential growth in the complexity of spatially inhomogeneous magnetization patterns. Far from being mere curiosities, phenomena arising from nonlocal interactions (including the joint action of 'distant dipolar fields' and radiation damping [7,8]) threaten to limit (or profoundly alter) the operation of state-of-the-art highfield high-resolution NMR spectrometers. They are equally important for understanding the dynamics of polarized quantum fluids including Bose-Einstein condensates [9], superfluid 3 He [10, 11], degenerate 3 He-4 He mixtures [12], and two-dimensional H gases [13]. From yet another perspective, the collective effects induced by distant dipolar fields can be used to amplify weak spin precession signals [14] and to enhance the sensitivity of precision searches for CP-violating permanent electric dipole moments [5].Here we describe NMR time reversal experiments that -for the first time -shed light on the extent to which the deleterious effects of spin turbulence can be controlled or suppressed. Moreover, they lay the foundatio...

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“…For laser manufacturers, the main technical challenge now lies in the cost-effective production of robust, reliable and very powerful fiber sources for production of large quantities of polarized gas to support the wide dissemination of established applications of hyperpolarized 3 He gas and the emergence of new ones [45,46,47,48,49,50,51,52,53,54,55].…”

Section: Resultsmentioning

confidence: 99%

A broadband ytterbium-doped tunable fiber laser for 3He optical pumping at 1083�nm

Tastevin

Grot

Courtade

et al. 2004

Applied Physics B: Lasers and Optics

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Large amounts of hyperpolarized 3 He 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 2 3 S-2 3 P 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, allfiber devices are built to provide robust, high power turn-key sources at 1083 nm for improved production of laser polarized 3 He. 42.55.Wd; 32.80.Bx PACS

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Cited by 13 publications

References 12 publications

NMR Time Reversal Experiments in Highly Polarised Liquid 3He-4He Mixtures

NMR Time Reversal Experiments in Highly Polarised Liquid 3He-4He Mixtures

NMR Time Reversal as a Probe of Incipient Turbulent Spin Dynamics

A broadband ytterbium-doped tunable fiber laser for 3He optical pumping at 1083�nm

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