Demonstration of relativistic electron beam focusing by a laser-plasma lens

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

All-optical Compton gamma-ray source

International audienceOne of the major goals of research for laser-plasma accelerators (1) is the realization of compact sources of femtosecond X-rays (2, 3, 4). 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 (5, 6). 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

Physics of fully-loaded laser-plasma accelerators

International audienceWhile 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

Monitoring shot-to-shot variations of soft x-ray sources using aluminum foils

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Controlled electron injection in a laser-plasma accelerator

International audienceA few years ago, several experiments showed that laser-plasma accelerators can produce high-quality electron beams, with quasi-monoenergetic energy distributions at the 100 MeV level. These experiments were performed by focusing a single ultra-short and ultraintense laser pulse into an underdense plasma. Here, we report on recent experimental results of electron acceleration using two counter-propagating ultra-short and ultraintense laser pulses. We demonstrate that the use of a second laser pulse provides enhanced control over the injection and subsequent acceleration of electrons into plasma wakefields. The collision of the two laser pulses provides a pre-acceleration stage which provokes the injection of electrons into the wakefield. The experimental results show that the electron beams obtained in this manner are collimated (5 mrad divergence), monoenergetic (with relative energy spread <10%), tuneable (between 50 and 250 MeV) and, most importantly, stable

Betatron oscillations of electrons accelerated in laser wakefields characterized by spectral x-ray analysis

International audienceRelativistic electrons accelerated by laser wakefields can produce x-ray beams from their motion in plasma termed betatron oscillations. Detailed spectral characterization is presented in which the amplitude of the betatron oscillations r is studied by numerical analysis of electron and x-ray spectra measured simultaneously. We find that r reaches as low as 1 μm in agreement with previous studies of radiation based on coherence and far-field spatial profile

Axiparabola: a long-focal-depth, high-resolution mirror for broadband high-intensity lasers

International audienceDiffraction puts a fundamental limit on the distance over which a light beam can remain focused. For about 30 years, several techniques to overcome this limit have been demonstrated. Here, we propose a reflective optics, namely, the axiparabola, that allows to extend the production of "dif-fraction-free" beams to high-peak-power and broadband laser pulses. We first describe the properties of this aspheric optics. We then analyze and compare its performances in numerical simulations and in experiments. Finally, we use it to produce a plasma waveguide that can guide an intense laser pulse over 10 millimeters

Full characterization of a laser-produced keV x-ray betatron source

International audienceThis paper presents the complete characterization of a kilo-electron-volt laser-based x-ray source. The main parameters of the electron motion (amplitude of oscillations and initial energy) in the laser wakefield have been investigated using three independent methods relying on spectral and spatial properties of this betatron x-ray source. First we will show studies on the spectral correlation between electrons and x-rays that is analyzed using a numerical code to calculate the expected photon spectra from the experimentally measured electron spectra. High-resolution x-ray spectrometers have been used to characterize the x-ray spectra within 0.8–3 keV and to show that the betatron oscillations lie within 1 µm. Then we observed Fresnel edge diffraction of the x-ray beam. The observed diffraction at the center energy of 4 keV agrees with the Gaussian incoherent source profile of full width half maximum <5 µm, meaning that the amplitude of the betatron oscillations is less than 2.5 µm. Finally, by measuring the far field spatial profile of the radiation, we have been able to characterize the electron's trajectories inside the plasma accelerator structure with a resolution better than 0.5 µm

Controlling the Phase-Space Volume of Injected Electrons in a Laser-Plasma Accelerator

International audienceTo take full advantage of a laser-plasma accelerator, stability and control of the electron beam parameters have to be achieved. The external injection scheme with two colliding laser pulses is a way to stabilize the injection of electrons into the plasma wave, and to easily tune the energy of the output beam by changing the longitudinal position of the injection. In this Letter, it is shown that by tuning the optical injection parameters, one is able to control the phase-space volume of the injected particles, and thus the charge and the energy spread of the beam. With this method, the production of a laser accelerated electron beam of 10 pC at the 200 MeV level with a 1% relative energy spread at full width half maximum (3.1% rms) is demonstrated. This unique tunability extends the capability of laser-plasma accelerators and their applications