K. Ta Phuoc

École Polytechnique, Paliseau, Île-de-France, France

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Publications (65)275.39 Total impact

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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.
    Nature Communications 11/2014; 6. DOI:10.1038/ncomms7860 · 10.74 Impact Factor
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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.
    CLEO: Science and Innovations; 06/2014
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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.
    Physical Review Letters 09/2013; 111(13):135002. DOI:10.1103/PhysRevLett.111.135002 · 7.73 Impact Factor
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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.
    Physics of Plasmas 09/2013; 20(6). DOI:10.1063/1.4810791 · 2.25 Impact Factor
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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.
    Nature Communications 05/2013; 4:1501. DOI:10.1038/ncomms2528 · 10.74 Impact Factor
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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.
    11th International Conference on Synchrotron Radiation Instrumentation (SRI 2012); 05/2013
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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.
    Review of Modern Physics 01/2013; 85(1). DOI:10.1103/RevModPhys.85.1 · 42.86 Impact Factor
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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.
    Plasma Physics and Controlled Fusion 11/2012; 54(12). DOI:10.1088/0741-3335/54/12/124023 · 2.39 Impact Factor
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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.
    Frontiers in Optics; 10/2012
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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.
    Applied Physics Letters 10/2012; 101(11). DOI:10.1063/1.4752114 · 3.52 Impact Factor
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    ABSTRACT: One of the major goals of research for laser-plasma accelerators is the realization of compact sources of femtosecond X-rays. In particular, using the modest electron energies obtained with existing laser systems, Compton scattering a photon beam off a relativistic electron bunch has been proposed as a source of high-energy and high-brightness photons. However, laser-plasma based approaches to Compton scattering have not, to date, produced X-rays above 1 keV. Here, we present a simple and compact scheme for a Compton source based on the combination of a laser-plasma accelerator and a plasma mirror. This approach is used to produce a broadband spectrum of X-rays extending up to hundreds of keV and with a 10,000-fold increase in brightness over Compton X-ray sources based on conventional accelerators. We anticipate that this technique will lead to compact, high-repetition-rate sources of ultrafast (femtosecond), tunable (X- through gamma-ray) and low-divergence (~1°) photons from source sizes on the order of a micrometre.
    Nature Photonics 04/2012; 6(5):308-311. DOI:10.1038/nphoton.2012.82 · 29.96 Impact Factor
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    ABSTRACT: We study pump requirements to produce femtosecond X-ray laser pulses at saturation from inner-shell transitions in the amplified spontaneous emission regime. Since laser-based betatron radiation is considered as the pumping source, we first study the impact of the driving laser power on its intensity. Then we investigate the amplification behavior of the K- α transition of nitrogen at 3.2 nm (395 eV) from radiative transfer calculations coupled with kinetics modeling of the ion population densities. We show that the saturation regime may be experimentally achieved by using PW-class laser-accelerated electron bunches. Finally, we show that this X-ray laser scheme can be extended to heavier atoms and we calculate pump requirements to reach saturation at 1.5 nm (849 eV) from the K- α transition of neon.
    Applied Physics B 03/2012; 106(4):809-816. DOI:10.1007/s00340-012-4912-1 · 1.63 Impact Factor
  • Physical Review Letters 02/2012; 108(6). DOI:10.1103/PhysRevLett.108.069901 · 7.73 Impact Factor
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    ABSTRACT: A density perturbation produced in an underdense plasma was used to improve the quality of electron bunches produced in the laser-plasma wakefield acceleration scheme. Quasi-monoenergetic electrons were generated by controlled injection in the longitudinal density gradients of the density perturbation. By tuning the position of the density perturbation along the laser propagation axis, a fine control of the electron energy from a mean value of 60 MeV to 120 MeV has been demonstrated with a relative energy-spread of 15 +/- 3.6%, divergence of 4 +/- 0.8 mrad and charge of 6 +/- 1.8 pC.
    Physics of Plasmas 01/2012; 19(6). DOI:10.1063/1.4725421 · 2.25 Impact Factor
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    ABSTRACT: High intensity femtosecond laser pulses can be used to generate X-ray radiation. In the laser wakefield process, when a high intensity laser pulse (<1018 W/cm2) is focused onto a gas jet target, it interacts with the instantaneously created under-dense plasma and excites a wakefield wave. In the wakefield electrons are trapped and accelerated to high energies in short distances. The electrons trapped in the wakefield can perform Betatron oscillations across the propagation axis and emit X-ray photons. The Betatron X-ray beam is broadband as the radiation emission has a synchrotron distribution. The X-ray beam is collimated and its pulse duration is femtosecond. For high resolution and phase contrast X-ray imaging applications, the important feature of the X-ray Betatron beam is the μm source size. Using ALLS 100 TW class laser system we demonstrate that the Betatron X-ray beam is both energetic and bright enough to produce single laser shot phase contrast imaging of complex objects located in air.
    Proceedings of SPIE - The International Society for Optical Engineering 01/2012; DOI:10.1117/12.2001554 · 0.20 Impact Factor
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    ABSTRACT: Bright femtosecond X-ray beams, with energies up to a few hundreds of keV, have been produced from Betatron oscillations and Compton scattering in a laser-plasma accelerator. The potential of Betatron radiation for phase contrast imaging has been demonstrated.
    Lasers and Electro-Optics (CLEO), 2012 Conference on; 01/2012
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    ABSTRACT: We show that the control and the mapping of the x-ray emission reveals unique features of the laser-plasma accelerator physics, including strong correlations between electron and x-ray beams, and density-dependence of electron injection position.
    Lasers and Electro-Optics (CLEO), 2012 Conference on; 01/2012
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    ABSTRACT: The features of Betatron x-ray emission produced in a laser-plasma accelerator are closely linked to the properties of the relativistic electrons which are at the origin of the radiation. While in interaction regimes explored previously the source was by nature unstable, following the fluctuations of the electron beam, we demonstrate in this Letter the possibility to generate x-ray Betatron radiation with controlled and reproducible features, allowing fine studies of its properties. To do so, Betatron radiation is produced using monoenergetic electrons with tunable energies from a laser-plasma accelerator with colliding pulse injection [J. Faure et al., Nature (London) 444, 737 (2006)]. The presented study provides evidence of the correlations between electrons and x-rays, and the obtained results open significant perspectives toward the production of a stable and controlled femtosecond Betatron x-ray source in the keV range.
    Physical Review Letters 12/2011; 107(25):255003. DOI:10.1103/PhysRevLett.107.255003 · 7.73 Impact Factor
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    ABSTRACT: The x-ray emission in laser-plasma accelerators can be a powerful tool to understand the physics of relativistic laser-plasma interaction. It is shown here that the mapping of betatron x-ray radiation can be obtained from the x-ray beam profile when an aperture mask is positioned just beyond the end of the emission region. The influence of the plasma density on the position and the longitudinal profile of the x-ray emission is investigated and compared to particle-in-cell simulations. The measurement of the x-ray emission position and length provides insight on the dynamics of the interaction, including the electron self-injection region, possible multiple injection, and the role of the electron beam driven wakefield.
    Physical Review Letters 11/2011; 107(21):215004. DOI:10.1103/PhysRevLett.107.215004 · 7.73 Impact Factor
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    ABSTRACT: Development of x-ray phase contrast imaging applications with a laboratory scale source have been limited by the long exposure time needed to obtain one image. We demonstrate, using the Betatron x-ray radiation produced when electrons are accelerated and wiggled in the laser-wakefield cavity, that a high-quality phase contrast image of a complex object (here, a bee), located in air, can be obtained with a single laser shot. The Betatron x-ray source used in this proof of principle experiment has a source diameter of 1.7 μm and produces a synchrotron spectrum with critical energy E(c)=12.3±2.5 keV and 10⁹ photons per shot in the whole spectrum.
    Optics Letters 07/2011; 36(13):2426-8. DOI:10.1364/OL.36.002426 · 3.18 Impact Factor

Publication Stats

1k Citations
275.39 Total Impact Points

Institutions

  • 2006–2014
    • École Polytechnique
      • LULI Laboratoire Pour l'Utilisation des Lasers Intenses
      Paliseau, Île-de-France, France
  • 2006–2013
    • Laboratoire de Rhumatologie Appliquée
      Lyons, Rhône-Alpes, France
  • 2003–2011
    • ENSTA Bretagne
      Brest, Brittany, France
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France
  • 2009
    • Imperial College London
      • Department of Physics
      London, ENG, United Kingdom