K. Ta Phuoc

Université Paris-Saclay, Lutetia Parisorum, Île-de-France, France

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Publications (77)298.41 Total impact

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    ABSTRACT: Laser wakefield acceleration permits the generation of ultra-short, high-brightness relativistic electron beams on a millimeter scale. While those features are of interest for many applications, the source remains constraint by the poor stability of the electron injection process. Here we present results on injection and acceleration of electrons in pure nitrogen and argon. We observe stable, continuous ionization-induced injection of electrons into the wakefield for laser powers exceeding a threshold of 7 TW. The beam charge scales approximately linear with the laser energy and is limited by beam loading. For 40 TW laser pulses we measure a maximum charge of almost 1 nC per shot, originating mostly from electrons of less than 10 MeV energy. The relatively low energy, the high charge and its stability make this source well-suited for applications such as non-destructive testing. Hence, we demonstrate the production of energetic radiation via bremsstrahlung conversion at 1 Hz repetition rate. In accordance with Geant4 Monte-Carlo simulations, we measure a gamma-ray source size of less than 100 microns for a 0.5 mm tantalum converter placed at 2 mm from the accelerator exit. Furthermore we present radiographs of image quality indicators.
    No preview · Article · Jan 2016
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    ABSTRACT: The development of compact laser-based synchrotron sources is a field of active research. Here we present recent results on an all-optical Compton backscattering source using laser-accelerated electrons and a plasma mirror, as introduced in [K. Ta Phuoc et al., Nature Photonics 6 (5) (2012) 308-311].Scattering of quasi-monoenergetic electrons of up to 200 MeV energy with their proper drive-beam leads to emission of femtosecond X-ray pulses, whose energies exceed 100 keV. We demonstrate that the photon yield from the source is sufficient to illuminate a centimeter-size sample placed 90 centimeters behind the source.
    Preview · Article · Dec 2015 · Physics Procedia
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    A. Döpp · E. Guillaume · C. Thaury · A. Lifschitz · K. Ta Phuoc · V. Malka
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    ABSTRACT: The energy gain in laser wakefield accelerators is limited by dephasing between the driving laser pulse and the highly relativistic electrons in its wake. Since this phase depends on both the driver and the cavity length, the effects of dephasing can be mitigated with appropriate tailoring of the plasma density along propagation. Preceding studies have discussed the prospects of continuous phase-locking in the linear wakefield regime. However, most experiments are performed in the highly non-linear regime and rely on self-guiding of the laser pulse. Due to the complexity of the driver evolution in this regime it is much more difficult to achieve phase locking. As an alternative we study the scenario of rapid rephasing in sharp density transitions, as was recently demonstrated experimentally. Starting from a phenomenological model we deduce expressions for the electron energy gain in such density profiles. The results are in accordance with particle-in-cell simulations and we present gain estimations for single and multiple stages of rephasing.
    Full-text · Article · Dec 2015
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    ABSTRACT: The advent of X-ray free-electron lasers has granted researchers an unprecedented access to the ultrafast dynamics of matter on the nanometre scale. Aside from being compact, seeded plasma-based soft X-ray lasers (SXRLs) turn out to be enticing as photon-rich sources (up to 1015 per pulse) that display high-quality optical properties. Hitherto, the duration of these sources was limited to the picosecond range, which consequently restricts the field of applications. This bottleneck was overcome by gating the gain through ultrafast collisional ionization in a high-density plasma generated by an ultraintense infrared pulse (a few 1018 W cm-2) guided in an optically pre-formed plasma waveguide. For electron densities that ranged from 3 × 1018 cm-3 to 1.2 × 1020 cm-3, the gain duration was measured to drop from 7 ps to an unprecedented value of about 450 fs, which paves the way to compact and ultrafast SXRL beams with performances previously only accessible in large-scale facilities.
    Full-text · Article · Nov 2015 · Nature Photonics
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    ABSTRACT: Ionization injection is a simple and efficient method to trap an electron beam in a laser plasma accelerator. Yet, because of a long injection length, this injection technique leads generally to the production of large energy spread electron beams. Here, we propose to use a shock front transition to localize the injection. Experimental results show that the energy spread can be reduced down to 10 MeV and that the beam energy can be tuned by varying the position of the shock. This simple technique leads to very stable and reliable injection even for modest laser energy. It should therefore become a unique tool for the development of laser-plasma accelerators.
    Full-text · Article · Nov 2015 · Scientific Reports
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    ABSTRACT: All-optical Compton sources are innovative, compact devices to produce high energy femtosecond X-rays. Here we present results on a single-pulse scheme that uses a plasma mirror to reflect the drive beam of a laser plasma accelerator and to make it collide with the highly-relativistic electrons in its wake. The accelerator is operated in the self-injection regime, producing quasi-monoenergetic electron beams of around 150 MeV peak energy. Scattering with the intense femtosecond laser pulse leads to the emission of a collimated high energy photon beam. Using continuum-attenuation filters we measure significant signal content beyond 100 keV and with simulations we estimate a peak photon energy of around 500 keV. The source divergence is about 13 mrad and the pointing stability is 7 mrad. We demonstrate that the photon yield from the source is sufficiently high to illuminate a centimeter-size sample placed 90 centimeters behind the source, thus obtaining radiographs in a single shot.
    Full-text · Article · Nov 2015 · Plasma Physics and Controlled Fusion
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    ABSTRACT: An important limit for energy gain in laser-plasma wakefield accelerators is the dephasing length, after which the electron beam reaches the decelerating region of the wakefield and starts to decelerate. Here, we propose to manipulate the phase of the electron beam in the wakefield, in order to bring the beam back into the accelerating region, hence increasing the final beam energy. This rephasing is operated by placing an upward density step in the beam path. In a first experiment, we demonstrate the principle of this technique using a large energy spread electron beam. Then, we show that it can be used to increase the energy of monoenergetic electron beams by more than 50%.
    Full-text · Article · Oct 2015 · Physical Review Letters
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    ABSTRACT: Betatron x-ray source from laser plasma interaction combines high brightness, few femtosecond duration and broad band energy spectrum. However, despite these unique features the Betatron source has a crippling drawback preventing its use for applications. Its properties significantly vary shot-to-shot and none of the developments performed so far resolved this problem. In this letter we present a simple method that allows to produce stable and bright Betatron x-ray beams. In addition, we demonstrate that this scheme provides polarized and easily tunable radiation. Experimental results show that the pointing stability is better than 10% of the beam divergence, with flux fluctuation of the order of 20% and a polarization degree reaching up to 80%
    Full-text · Article · Sep 2015
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    ABSTRACT: While large efforts have been devoted to improving the quality of electron beams from laser plasma accelerators, often to the detriment of the charge, many applications do not require very high quality but high-charge beams. Despite this need, the acceleration of largely charged beams has been barely studied. Here we explore both experimentally and numerically the physics of highly loaded wakefield acceleration. We find that the shape of the electron spectra is strikingly independent of the laser energy, due to the emergence of a saturation effect induced by beamloading. A transition from quasi-Maxwellian spectra at high plasma densities to flatter spectra at lower densities is also found, which is shown to be produced by the wakefield driven by the electron bunch itself after the laser depletion.
    Full-text · Article · Jun 2015 · Physical Review Special Topics - Accelerators and Beams
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    ABSTRACT: Laser-plasma technology promises a drastic reduction of the size of high energy electron accelerators. It could make free electron lasers available to a broad scientific community, and push further the limits of electron accelerators for high energy physics. Furthermore the unique femtosecond nature of the source makes it a promising tool for the study of ultra-fast phenomena. However, applications are hindered by the lack of suitable lens to transport this kind of high-current electron beams, mainly due to their divergence. Here we show that this issue can be solved by using a laser-plasma lens, in which the field gradients are five order of magnitude larger than in conventional optics. We demonstrate a reduction of the divergence by nearly a factor of three, which should allow for an efficient coupling of the beam with a conventional beam transport line.
    Full-text · Article · Nov 2014 · Nature Communications
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    ABSTRACT: X-ray radiation emitted by electrons during their acceleration in a laser-plasma accelerator was used to evidence two distincts self-injection mechanisms (longitudinal and transverse) and to identify one source of angular-momentum growth in laser-plasma accelerators.
    No preview · Conference Paper · Jun 2014
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    ABSTRACT: The transverse properties of an electron beam are characterized by two quantities, the emittance which indicates the electron beam extent in the phase space and the angular momentum which allows for nonplanar electron trajectories. Whereas the emittance of electron beams produced in a laser-plasma accelerator has been measured in several experiments, their angular momentum has been scarcely studied. It was demonstrated that electrons in a laser-plasma accelerator carry some angular momentum, but its origin was not established. Here we identify one source of angular-momentum growth and we present experimental results showing that the angular-momentum content evolves during the acceleration.
    Full-text · Article · Sep 2013 · Physical Review Letters
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    ABSTRACT: While laser-plasma accelerators have demonstrated a strong potential in the acceleration of electrons up to giga-electronvolt energies, few experimental tools for studying the acceleration physics have been developed. In this paper, we demonstrate a method for probing the acceleration process. A second laser beam, propagating perpendicular to the main beam is focused in the gas jet few nanosecond before the main beam creates the accelerating plasma wave. This second beam is intense enough to ionize the gas and form a density depletion which will locally inhibit the acceleration. The position of the density depletion is scanned along the interaction length to probe the electron injection and acceleration, and the betatron X-ray emission. To illustrate the potential of the method, the variation of the injection position with the plasma density is studied.
    Full-text · Article · Sep 2013 · Physics of Plasmas
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    ABSTRACT: Laser-plasma accelerators can produce high-quality electron beams, up to giga electronvolts in energy, from a centimetre scale device. The properties of the electron beams and the accelerator stability are largely determined by the injection stage of electrons into the accelerator. The simplest mechanism of injection is self-injection, in which the wakefield is strong enough to trap cold plasma electrons into the laser wake. The main drawback of this method is its lack of shot-to-shot stability. Here we present experimental and numerical results that demonstrate the existence of two different self-injection mechanisms. Transverse self-injection is shown to lead to low stability and poor-quality electron beams, because of a strong dependence on the intensity profile of the laser pulse. In contrast, longitudinal injection, which is unambiguously observed for the first time, is shown to lead to much more stable acceleration and higher-quality electron beams.
    Full-text · Article · May 2013 · Nature Communications
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    ABSTRACT: The LUNEX5 (free electron Laser Using a New accelerator for the Exploitation of X-ray radiation of 5th generation) in France aims at investigating the generation of short, intense, and coherent pulses in the soft x-ray region (with two particular targeted wavelengths of 20 and 13 nm). It consists in a single Free Electron Laser (FEL) line with cryo-ready in-vacuum undulators using a Conventional Linear Accelerator (CLA) using the superconducting technology of 400 MeV or a Laser Wake Field Accelerator (LWFA) ranging from 0.4 to 1 GeV with multi-TW or PW lasers. The FEL line can be operated in the seeded (High order Harmonic in Gas seeding) and Echo Enable Harmonic Generation configurations, which performances will be compared. Two pilot user experiments for time-resolved studies of isolated species and magnetization dynamics will take benefit of LUNEX5 FEL radiation.
    Full-text · Conference Paper · Mar 2013
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    ABSTRACT: Relativistic interaction of short-pulse lasers with underdense plasmas has recently led to the emergence of a novel generation of femtosecond x-ray sources. Based on radiation from electrons accelerated in plasma, these sources have the common properties to be compact and to deliver collimated, incoherent and femtosecond radiation. In this article we review, within a unified formalism, the betatron radiation of trapped and accelerated electrons in the so-called bubble regime, the synchrotron radiation of laser-accelerated electrons in usual meter-scale undulators, the nonlinear Thomson scattering from relativistic electrons oscillating in an intense laser field, and the Thomson backscattered radiation of a laser beam by laser-accelerated electrons. The underlying physics is presented using ideal models, the relevant parameters are defined, and analytical expressions providing the features of the sources are given. Numerical simulations and a summary of recent experimental results on the different mechanisms are also presented. Each section ends with the foreseen development of each scheme. Finally, one of the most promising applications of laser-plasma accelerators is discussed: the realization of a compact free-electron laser in the x-ray range of the spectrum. In the conclusion, the relevant parameters characterizing each sources are summarized. Considering typical laser-plasma interaction parameters obtained with currently available lasers, examples of the source features are given. The sources are then compared to each other in order to define their field of applications.
    Full-text · Article · Jan 2013 · Review of Modern Physics
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    ABSTRACT: Betatron x-ray emission in laser-plasma accelerators is a promising compact source that may be an alternative to conventional x-ray sources, based on large scale machines. In addition to its potential as a source, precise measurements of betatron emission can reveal crucial information about relativistic laser-plasma interaction. We show that the emission length and the position of the x-ray emission can be obtained by placing an aperture mask close to the source, and by measuring the beam profile of the betatron x-ray radiation far from the aperture mask. The position of the x-ray emission gives information on plasma wave breaking and hence on the laser non-linear propagation. Moreover, the measurement of the longitudinal extension helps one to determine whether the acceleration is limited by pump depletion or dephasing effects. In the case of multiple injections, it is used to retrieve unambiguously the position in the plasma of each injection. This technique is also used to study how, in a capillary discharge, the variations of the delay between the discharge and the laser pulse affect the interaction. The study reveals that, for a delay appropriate for laser guiding, the x-ray emission only occurs in the second half of the capillary: no electrons are injected and accelerated in the first half.
    Full-text · Article · Nov 2012 · Plasma Physics and Controlled Fusion
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    ABSTRACT: Bright and high-energy femtosecond x-ray beams were produced from Betatron oscillations and Compton scattering in laser-plasma accelerators. Their use as a diagnostic for laser-plasma accelerators and for applications was demonstrated.
    No preview · Conference Paper · Oct 2012
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    ABSTRACT: Using a laser plasma accelerator, experiments with a 80 TW and 30 fs laser pulse demonstrated quasi-monoenergetic electron spectra with maximum energy over 0.4 GeV. This is achieved using a supersonic He gas jet and a sharp density ramp generated by a high intensity laser crossing pre-pulse focused 3 ns before the main laser pulse. By adjusting this crossing pre-pulse position inside the gas jet, among the laser shots with electron injection more than 40% can produce quasi-monoenergetic spectra. This could become a relatively straight forward technique to control laser wakefield electron beams parameters.
    Full-text · Article · Oct 2012 · Applied Physics Letters
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    Conference Paper: The LUNEX5 project
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    ABSTRACT: LUNEX5 (free electron Laser Using a New accelerator for the Exploitation of X-ray radiation of 5th generation) aims at investigating the production of short, intense, and coherent pulses in the soft X-ray region. The project consists of a Free Electron Laser (FEL) line enabling the most advanced seeding configurations: High order Harmonic in Gas (HHG) seeding and Echo Enable Harmonic Generation (EEHG) with in-vacuum (potentially cryogenic) undulators of 15 and 30 mm period. Two accelerator types feed this FEL line : a 400 MeV Conventional Linear Accelerator (CLA) using superconducting cavities compatible with a future upgrade towards high repetition rate, for the investigations of the advanced FEL schemes; and a 0.4 - 1 GeV Laser Wake Field Accelerator (LWFA), to be qualified in view of FEL application, in the single spike or seeded regime. Two pilot user experiments for time- resolved studies of isolated species and solid state matter dynamics will take benefit of LUNEX5 FEL radiation and provide feedback of the performance of the different schemes under real user conditions.
    Full-text · Conference Paper · Aug 2012

Publication Stats

1k Citations
298.41 Total Impact Points

Institutions

  • 2015
    • Université Paris-Saclay
      Lutetia Parisorum, Île-de-France, France
  • 2006-2014
    • École Polytechnique
      • • Laboratoire d'Optique Appliquée (LOA)
      • • LULI Laboratoire Pour l'Utilisation des Lasers Intenses
      Paliseau, Île-de-France, France
  • 2006-2013
    • Laboratoire de Rhumatologie Appliquée
      Lyons, Rhône-Alpes, France
  • 2009-2011
    • Imperial College London
      • Department of Physics
      Londinium, England, United Kingdom
  • 2003-2011
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France
    • ENSTA Bretagne
      Brest, Brittany, France