Stable femtosecond X-rays
Technology based on high peak power lasers has the potential to provide compact and intense radiation sources for a wide range of innovative applications. In particular, electrons accelerated in the wakefield of an intense laser pulse will oscillate around the propagation axis and emit X-rays. This betatron source, which essentially reproduces the principle of synchrotron on a millimeter scale, provides bright radiation with femtosecond duration and high spatial coherence. But despite its unique features, the usability of the source has been constrained by its poor control and stability. In this letter, we demonstrate reliable production of X-ray beams with tunable polarization. Using ionization-induced injection in a gas mixture, the orbits of the relativistic electrons emitting the radiation are reproducible and controlled. We observe that both signal and beam profile fluctuations are significantly reduced, and the beam pointing varies less than a tenth of the beam divergence. The polarization ratio reaches up to 80 percent and the polarization axis can be easily rotated. We anticipate a broad impact of the source as its unprecedented performance opens the way to new applications.
These results have been published in LIGHT, november 2017
Caption: Betatron radiation beam profiles in the classical (transverse injection) and recently studied (ionization injection) regimes.
High rep rate laser-plasma accelerators
- April 10th, 2017 - laser-plasma accelerators demonstrated with high repetition rate and compact laser systems (Nature Photonics)
Laser–plasma acceleration is an emerging technique for accelerating electrons to high energies over very short distances. The accelerated electron bunches have femtosecond duration, making them particularly relevant for applications such as ultrafast imaging or femtosecond X-ray generation. Current laser–plasma accelerators deliver 100 MeV to GeV electrons using Joule-class laser systems that are relatively large in scale and have low repetition rates, with a few shots per second at best. Nevertheless, extending laser–plasma acceleration to higher repetition rates would be extremely useful for applications requiring lower electron energy. Here, we use single-cycle laser pulses to drive high-quality MeV relativistic electron beams, thereby enabling kHz operation and dramatic downsizing of the laser system. Numerical simulations indicate that the electron bunches are only ∼1 fs long. We anticipate that the advent of these kHz femtosecond relativistic electron sources will pave the way to applications with wide impact, such as ultrafast electron diffraction in materials with an unprecedented sub-10 fs resolution.
"Relativistic electron beams driven by kHz single-cycle light pulses"
D. Guénot, D. Gustas, A. Vernier, B. Beaurepaire, F. Böhle, M. Bocoum, M. Lozano, A. Jullien, R. Lopez-Martens, A. Lifschitz and J. Faure*
Nature Photonics (2017)
doi:10.1038/nphoton.2017.46, Published online 10 April 2017
FET-OPEN awarded to LOA
- November 4th, 2016 - An European FET-OPEN program of 3,9 M€, Laser Lightning Rod (LLR), has been awarded to a consortium leaded by Aurelien HOUARD at LOA.
Controlling lightning is a long time dream of mankind. The goal of the present project is to investigate and develop a new type of lightning protection based on the use of upward lightning discharges initiated through a high repetition rate multi terawatt laser. The feasibility of the novel technique and the project’s prospect of success are based on recent research providing new insights into the mechanism responsible for the guiding of electrical discharges by laser filaments, on cutting-edge high power laser technology and on the availability of the uniquely suitable Säntis lightning measurement station in Northeastern Switzerland (2500 m).
The LLR consortium is ideally positioned to succeed and to raise the competitiveness of Europe in lightning control as it relies on the integration of trans-disciplinary fields in laser development, nonlinear optics, plasma physics, remote sensing, and lightning: The project team is made up of leaders in the domains of high power nonlinear propagation of laser pulses in the atmosphere, laser control of electric discharges, lightning physics, high power laser development, and high-repetition-rate lasers. In addition, the largest European company in aeronautics brings its expertise in lightning direct effects and protection means on aircraft and infrastructures.
This is the second FET-OPEN contract awarded to LOA.
4% over the 522 eligible projects have been awarded.
The consortium: LOA (coordinator), EPFL, Université de Genève, Trumpf, Airbus GI, HESSO
More information: http://llr-fet.eu
ERC starting awarded at LOA
- September 1st, 2016 - An ERC starting grant has been awarded to a researcher at LOA, Sebastien Corde, on the development of a novel plasma particle acceleration technology .
As we push the frontier of particle physics to higher particle energies, conventional accelerator techniques are attaining their limits and new concepts are emerging. The use of an ionized gas —or plasma— circumvents the most significant barrier of conventional techniques by increasing the energy gained per unit length by several orders of magnitude. One class of plasma accelerators, relevant for high energy physics applications, consists in using a particle beam, « the driver », to excite a plasma wave, that is then used to accelerate the main particle beam. Research in this field requires large facilities, due to stringent conditions on the driver. In the M-PAC project (Miniature beam-driven Plasma ACcelerators), I propose to power plasma accelerators with laser-accelerated electron beams based on 100-TW-class laser systems, so as to miniaturize the so-called “beam-driven plasma accelerators”. The project crosses the boundary of the fields of research of laser acceleration and of beam- driven plasma acceleration. With these innovative miniature versions, the goal of the M-PAC project is then to tackle, through experiments and simulations, the next Grand Challenges facing the field of beam-driven plasma acceleration, bringing plasma accelerator technology to viability for high energy physics collider applications. They include the generation and preservation of the excellent beam quality required for high- energy colliders and next-generation light sources, the demonstration of high drive-to-main-beam energy efficiency and the acceleration of the antimatter counterpart of the electron, the positron. Finally, the miniature beam-driven plasma accelerators open new opportunities to push university-scale plasma-based light sources to the next level, both in terms of brightness and spectral range.
This is the ERC number 6 awarded to LOA researchers since the launch of the program in 2009.
plasma accelerators driven by particle beams
- June 23rd, 2016 - An international team involving a scientist from LOA has published two studies in the journal Nature Communications, improving the capabilities and the understanding of plasma accelerators driven by particle beams.
In the first study [Nat. Commun. 7, 11785 (2016)], the researchers were able to create a new type of plasma accelerator, taking the form of a hollow plasma channel – a tube of plasma with neutral gas on the inside. With this particular geometry, particles flying in the tube won’t experience transverse forces that can be detrimental to the quality of the beam. This is critical for the positron, the antimatter sibling of the electron, whose acceleration in plasma is extremely challenging. By sending a beam of positrons into the tube, the authors were able to excite a wakefield that can be used for the acceleration of positrons, and that is free of unwanted transverse forces.
In the second study [Nat. Commun. 7, 11898 (2016)] lead by Sebastien Corde from LOA, the scientists have investigated the dynamics and interaction of an electron beam with self-produced plasma. In this case, the plasma is directly generated by the ionization of a gas by the electron beam itself. When the beam travels through a high-ionization-potential gas (such as argon), as in the reported experiment, the conditions are expected to be strongly unfavorable for plasma acceleration and very small gain of energy (sub-GeV) was anticipated. Instead, surprisingly large energy gains, up to 27 GeV, were experimentally observed, in disagreement with expectations.
The results have revealed two key phenomenons that are taking place and make this very high-field acceleration possible. First, the beam undergoes self-focusing: its beam size is rapidly reduced and then maintained at its minimum value so that the beam becomes very dense and can drive high-field plasma wakes (see figure). Second, such a beam does not undergo continuous head erosion, because the particles at the head of the bunch have very low divergence and they provide an onset of ionization sufficient to provide guidance for the rest of the beam.
These unexpected and surprising results provide a more complete understanding of the interaction between beams and plasmas, which will certainly guide future optimizations of beam-driven plasma accelerators.
S. Gessner et al., Nat. Commun. 7, 11785 (2016) - http://dx.doi.org/10.1038/ncomms11785
S. Corde et al., Nat. Commun. 7, 11898 (2016) - http://dx.doi.org/10.1038/ncomms11898
2016 E. Fabre prize awaeded to J. Faure
The prize “Edouard Fabre 2016” for contributions to the physics of laser-driven inertial confinement fusion and laser-produced plasmas has been assigned to Jerome Faure, LOA. The Prize is especially addressed to researchers in full activity, within about 15 years after obtaining their Ph.D.
In 2003, J. Faure obtained a CNRS position at Laboratoire d’Optique Appliquée where he performed remarkable experimental work in developing laser-plasma accelerators, demonstrating the possibility of using laser-plasma interaction to accelerate electrons in extremely short distances and producing high quality electron beam. In 2012, he got an ERC Starting grant to produce with a kHz laser system, femtosecond electron bunches and to apply them for the study of ultra fast phenomena using electron diffraction with femtosecond time resolution. In parallel Jerome Faure teaches quantum physics and statistical physics as Associated Professor at Ecole Polytechnique. He is now a CNRS research director and the head of the APPLI research group at LOA (Application of ultrafast sources to solid state physics).
more information here
First ENSTA-ParisTech MOOC
- February 9th, 2016 - The first MOOC of ENSTA-ParisTech was posted on February 4, 2016 in FUN, the French e-learning platform. Davide Boschetto, researcher at LOA laboratory, offers a first course on the Introduction to Quantum Physics. 5 days following its launch, more than 600 e-students have already registered. The course will start April 25th, 2016. FUN includes more than 50 partners in France and around the world, among with ENSTA-ParisTech.
Vacuum laser acceleration of relativistic electron
- December 21st, 2015 - Two teams from CEA LIDYL and Laboratory for Applied Optics (LOA) at ENSTA-ParisTech - Ecole Polytechnique - CNRS were able to demonstrate for the first time the vacuum acceleration of electrons to relativistic energies by an intense laser beam. These results are published in Nature Physics (december 2015). This observation shows that it is possible to take benefit of the very strong amplitudes of the electric field of femtosecond laser pulses that are used today to accelerate high-energy particles over short distances.
By concentrating the light over periods of femtoseconds (10-15 s) durations, the laser pulses can reach very high instantaneous light powers (~ 1 PW or 1015 W) and hence extremely high amplitudes of the associated electric field (~ 10 TéraV/m or 1013 V/m).
Like the large sea waves off the coast that can not move ships, this oscillating field can not accelerate at very high energy charged particles. But like the surfer who is at first providing speed on its own to catch the wave and then continuously enjoy its slope, the injection of relativistic electrons in the laser beam (with a speed very close to that of light) can theoretically enable its acceleration, taking the full advantage of extremely high electric fields associated with the ultrashort laser pulse.
Many teams around the world have tried to demonstrate this phenomenon, without being able to provide convincing proof up to now. LOA and LYDIL researchers show that the interaction of the laser pulse with a solid target (plasma mirror) provides the ideal electron injection conditions. Electrons have been accelerated to about 10 MeV energies over a distance of 80 micrometers. This experiment paves the way to realize ultra-compact electron accelerators of very high energies.
Caption: Electron beam profile from the plasma mirror. The colors reflect the number of electrons emitted in a given direction. Deflected due to the acceleration of 1.5 MeV to 10 MeV over a distance of 80 microns by the laser pulse, the high energy electron beam is visible at the center of the figure (red spot), while very few electrons are emitted in the direction of the reflected light beam (white spot). © F. Quéré (CEA) - J. Faure (CNRS).
Femtosecond x-ray laser
- November 16th, 2015 - For over a decade, the duration of flashes of XUV laser radiation generated from laser-plasma interaction was limited to a few picoseconds, reducing access to many pioneering and innovative applications in the ultrafast range. A team of the Laboratory of Applied Optics (LOA) led by Stéphane Sebban has just published in the journal Nature Photonics results demonstrating, for the first time, that intense femtosecond pulse duration can be obtained. The amplifying medium is a plasma of nickelloïd krypton emitting at 32.8 nm which was injected by a source of high-order harmonics obtained in argon. Laboratory-size applications previously limited to large infrastructures such as synchrotrons or free electron lasers become feasible. This work was carried out in cooperation with the LPGP (University Orsay), the ELI-Beamlines Project (Prague), the APRI Laboratory (Gwangju, South Korea) and LULI (Ecole Polytechnique, Palaiseau).
More information :
- Article : Table-top femtosecond soft X-ray laser by collisional ionization gating, A. Depresseux et al., Nature Photonics, Published online 16 November 2015
- Press release
- Nature, S. Corde et al, august 27th, 2015 - For several years, plasma accelerators have shown their tremendous ability to accelerate particle beams. One objective is to downsize the experimental facilities and to allow the generation of very high energies while keeping the infrastructures within achievable size. To date, plasmas created by laser based on the interaction of an intense femtosecond laser with the matter or plasmas created by electron beams generated from RF accelerators, have accelerated energetic electrons with remarkable properties like ultrafast pulse duration, charge, energy or compactness in the case of lasers.
Sébastien Corde, researcher at LOA, has this time shown (Nature on August 27, 2015) with an international team working on the SLAC-FACET infrastructure at Stanford (USA), how these plasmas can be used to accelerate an other type of particles, the positrons. A positron beam with an initial energy of 20 GeV could gain 5 GeV by capturing about 30% of the energy of the plasma. These results are an important step toward the realisation of the next generation of particle colliders.
- Illustration: Weiming An (UCLA)
- More information: