LKB - Polarised Helium, Quantum Fluids and Solids

Research

News and Events

Regular article

Stimulated Brillouin gain spectroscopy in a confined spatio-temporal domain (30 μm, 170 ns) L. Djadaojee, A. Douillet, J. Grücker

Eur. Phys. J. Appl. Phys. 89, 30701 (2020)
[5 pages] Open access

Graphical abstract EPJAP 850px

© Mathieu Djadaojee

Abstract

The Brillouin gain spectrum of a test sample (liquid acetone at room temperature) on scales simultaneously confined in space (~30 μm) and time (~170 ns) is reported. This is done using a pulsed stimulated Brillouin scattering gain spectrometer in a θ ≈ 90° crossing beam configuration. After having identified and corrected for different sources of background signals, we obtained a Brillouin gain spectrum allowing an accurate measurement (MHz range) of the Brillouin frequency (few GHz). This is of interest for probing acoustic properties of transparent media subjected to repetitive fast transient phenomena on small length scales.

Regular article

A fast MOSFET RF switch for low-field NMR and MRI P.-J. Nacher, S. Kumaragamage, G. Tastevin, C.P. Bidinosti. ⟨hal-02266979⟩ [8 pages]

J. Magn. Reson. 310, 106638 (2020)

Abstract

TRansmit Array Spatial Encoding (TRASE) MRI uses trains of rf pulses alternatively produced by distinct transmit coils. Commonly used coil switching involving PIN diodes is too slow for low-field 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-μs 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 three-fold acceleration of TRASE phase-encoding is demonstrated when MOSFET switches are used instead of fast reed relays.

Regular article

Signal feedback applications in low-field NMR and MRI V. Kuzmin, P.-J. Nacher ⟨hal-02069159⟩ [17 pages]

J. Magn. Reson. 310, 106622 (2020)

Abstract

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 3He without or with radiation damping. The moderate intrinsic Q-factor (≈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≈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.

Regular article

Nuclear hyperpolarization of ³He by magnetized plasmas
Maul A., Blümler P., Nacher P.-J., Otten E., Tastevin G., and Heil W.

Phys. Rev. A (2018) 98, 063405 [12 pages]

Abstract

We describe a method to hyperpolarize ³He nuclear spins at high magnetic fields (4.7 T) solely by a magnetized plasma. The conditions for such a magnetized plasma are fulfilled when the mean free path of the free electrons is much larger than their gyration radius in the rf gas discharge. Investigations are carried out in the 1-15 mbar pressure range with rf excitation at ~100 MHz. Quantitative NMR measurements show that, for different cell sizes and ³He gas densities, nuclear polarizations in the range 1% to 9% are observed. We explain this phenomenon by an alignment-to-orientation conversion mechanism in the excited 2³P state of ³He which is most efficient when the Zeeman and the spin-orbit energies are comparable. The 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.

Review article

Optically polarized ³He

T. R. Gentile, P. J. Nacher, B. Saam, and T. G. Walker

Rev. Mod. Phys. 89, 045004 (2017)

Archives

Science outreach

Lionel Djadaojee

Français

Ce que nous inspirent la beauté et l’harmonie des lois

Dernière édition: 23 Janvier 2020, 19h – Sorbonne université, Campus Pierre et Marie Curie (Amphithéâtre 15),4 place Jussieu, 75005 Paris

« A chaque fois que nous examinons un problème en profondeur, le même frisson, le même émerveillement et le même mystère ne cessent de revenir » Feynman

Un scientifique qui tente de pénétrer les mystères du monde peut parfois éprouver l’impression vive d’être en contact avec une énigme, une beauté singulière. Cette soirée propose d’évoquer ce pressentiment d’une profonde harmonie du monde et d’une réalité qui lui échappe…

Soirées à l’initiative de

  • Lionel DJADAOJEE (Ancien normalien; agrégé de Physique, enseignant à l’ENS et doctorant ENS-PSL)
  • Philippe PINEAU (Ingénieur)
  • Christophe RICHARD (Professeur agrégé de Mathématiques).

English

The wonder in science

Last event: January 23, 2020, 7 pm – Sorbonne université, Campus Pierre et Marie Curie (Amphithéâtre 15),4 place Jussieu, 75005 Paris

“The same thrill, the same awe and mystery, come again and again when we look at any problem deeply enough. With more knowledge comes deeper, more wonderful mystery, luring one on to penetrate deeper still.” Richard Feynman

A scientist who tries to unravel the mysteries of the world can sometimes have the lively impression of being in contact with an enigma, a singular beauty. The evening events are intended to put forward the intuitive sense of a deep harmony of the world and a reality that is slipping away…

Events initiated by:

  • Lionel DJADAOJEE (Teaching assistant at ENS – Physics. PhD student at ENS-PSL)
  • Philippe PINEAU (Engineer)
  • Christophe RICHARD (Professor – Mathematics).

 

Review article

Metastable phases of liquid and solid 4He  Jules Grücker

J. Low Temp. Phys. 197, 149–166 (2019)

Abstract

Experiments and theories describing the metastable phases of liquid and solid 4He are presented and discussed. For the case of metastable liquid 4He with respect to its gaseous phase, it is shown that different measurements of its destabilization threshold (cavitation threshold) and their comparison to available theories reveal that the nucleation mechanism is not totally under- stood. Then experiments measuring typical lifetime of cavitation bubbles in He I and He II are shortly considered showing the important role of heat trans- port mechanism during their collapse. Finally for liquid 4He, its metastability with respect to its solid phase and the possibility of the liquid destabilization due to the vanishing of the roton gap is presented. The last part of the review is devoted to metastable solid 4He with respect to its liquid phase. The first experimental production of such a state is described and its destabilization limit possibly invoking the creation and proliferation of crystalline defects is discussed.

The MARGIN project

MARGIN (2020-2022, ANR-RSF support) mainly deals with MAgnetic Resonance studies of Gas diffusion In Nanoporous materials. Investigations focus on  of the influence of gas-wall interactions on NMR diffusion measurements.

See the post on the Russian Science Foundation portal (October 17, 2019) and follow the link to the project description.

Summary   RésuméProject overview

PhD student

Lionel DJADAOJEE (Teaching assistant at ENS Paris – PSL, Agrégé de Physique) has joined the group for PhD work on the metastable phases of solid and liquid 4He (J. Grücker, superviser; Sept. 2019 – …).

Winners

March 2019, PSL-iTeams closing session.

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MULSA (an ecologically responsible alternative to conventional foam board) has been selected as best project at the end of the 2018/2019 PSL-iTeams training program (entrepreneurship education for PSL Master and PhD students, promoting interdiscplinarity and innovation). The project has been designed and defended on March 26 by Fiona Guillemant (ENSAD 2018), Baptiste Lefebvre ( PhD student, ENS), and Ali Dia.

In memoriam

Philippe Jacquier, leader of the “Quantum solid and liquid helium” team since 2003, passed away on Jan.24, 2019.

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Philippe has battled against disease for many years with impressive courage and steadfast determination. He was an excellent teacher and a passionate researcher. The group will long miss his deep sense of humour and friendship, as well as the enthousiasm, the inventiveness, the curiosity, and the broad knowledge that made working with him so pleasant every day.

Short text (in French) by Antoine Heidmann, Director of the LKB.Ph. Jacquier’s scientific homepage

People

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Polarised He & quantum fluids
Quantum solid & liquid He
  • Franck Laloë
  • Pierre-Jean Nacher
  • Geneviève Tastevin
  • Polar. 3He - Other People
  • Ali Dia
  • Jules Grucker
  • Solid 4He - Other people
  • Lionel Djadaojee

Recent Papers

A. Maul, P. Blümler, P.-J. Nacher, E. Otten, G. Tastevin, and W. Heil

Phys. Rev. A 98, 063405 (2018)

Jules Grucker

J. Low. Temp. Phys (2019), First Online: 15 July 2019 [18 pages]

An Qu, Azer Trimeche, Philippe Jacquier and Jules Grucker

Phys. Rev. B (2016), 93, 174521

Tastevin G. and Laloë F.

Eur. Phys. J. D 72: 183 (2018)

T. R. Gentile, P. J. Nacher, B. Saam, and T. G. Walker

Rev. Mod. Phys. 89, 045004 (2017)

M.E. Hayden, and P.-J. Nacher

Magn. Reson. Imaging Handbook, 1, CRC press, 2016 (Ed. Luca SABA)

JOB OFFERS

2019-2020 - Master / PhD

High-field polarisation of helium - 3 (with or without laser light)

We offer two types  of internship work (instrumental, experimental)for Master students (M1 our M2)  in connection with on-going studies of laser-induced and discharge-induced orientation of the nuclear spin in helium plasmas. Topic opened for PhD: High-field hyperpolarisation in helium plasmas

2019-2020 - Master 2 / PhD

 

Polarised helium - Low field MRI

Skilled and motivated students are welcome to join our investigations on low field MRI with laser-polarised ³He gas or thermally-polarised water samples. Work may focus on the impact of concomitant field gradients on image quality, or investigate the short-pulse limit and revisit the Bloch-Siegert effect in NMR. This topic is open for PhD.

2019-2020 - Master 2

 

Polarised helium - Liquid NMR

Skilled and motivated students are welcome to join the team for follow-up of our investigations on liquid NMR in laser polarised ³He-⁴He dilute solutions. Work will deal with the latest observations of non linear NMR dynamics and will focus on the comparison between experimental and numerical data. This topic is not open for PhD this year.

We are always looking for brillant motivated scientists to join our group.

Check the open positions (see above) or send us your CV for application.

CONTACT

Département de Physique Ecole Normale Supérieure, 24 rue Lhomond, F-75231 Paris Cedex 05  

  •  Jules Grucker  : jules.grucker at lkb.ens.fr
  • Franck Laloë : laloe at lkb.ens.fr
  • Pierre-Jean Nacher : nacher at lkb.ens.fr
  • Geneviève Tastevin : genevieve.tastevin at lkb.ens.fr

Nos Tutelles et Partenaires

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