International audienceThis article gives a detailed description of a single shot electron spectrometer which was used to characterize electron beams produced by laser-plasma interaction. Contrary to conventional electron sources, electron beams from laser-plasma accelerators can produce a broad range of energies. Therefore, diagnosing these electron spectra requires specific attention and experimental development. Here, we provide an absolute calibration of the Lanex Kodak Fine screen on a laser-triggered radio frequency picosecond electron accelerator. The efficiency of scintillating screens irradiated by electron beams has never been investigated so far. This absolute calibration is then compared to charge measurements from an integrating current transformer for quasimonoenergetic electron spectra from laser-plasma interaction

Beams of fast electrons have been generated from the ultra-intense laser interaction (6×1019W cm−2, 40fs) with aluminum foil targets. The dynamics of fast-electron propagation as well as the level of induced in-depth heating have been investigated using the optical emission from the foil’s rear side. The dependence of the emitted signals spectrum and size on the target thickness allowed the identification of the coherent (coherent transition radiation) and incoherent (thermal radiation) mechanisms of the optical emission. We demonstrate a two-temperature energy distribution for the laser-generated fast-electron population: a divergent bulk component (θbulk=35°±5°) with ≈35% of the laser focal spot energy and a 400–600keV temperature, plus a relativistic tail highly collimated (θtail=7°±3°), with a 10MeV temperature and a periodic modulation in microbunches, representing less than 1% of the laser energy. Important yields of thermal emission, observed for targets thinner than 50μm, are consequence of a hot plasma near the front surface. The important heating at shallow depth (<15μm) results from collective mechanisms associated to the fast-electron transport, in particular from a resistive heating upon the neutralizing return current of background electrons. For deeper layers, because of the bulk component divergence, the fast-electron energy losses are dominated by collisions.

We present a protocol to characterize the high energy electron beam emitted in the interaction of an ultraintense laser with matter at intensities higher than 10(19) W cm(-2). The electron energies and angular distributions are determined as well as the total number of electrons produced above a 10 MeV threshold. This protocol is based on measurements with an electron spectrometer and nuclear activation techniques, combined with Monte Carlo simulations based on the GEANT3 code. The method is detailed and exemplified with data obtained with polypropylene and copper thin solid targets at a laser intensity of 2x10(19) W cm(-2). Special care is taken of the different sources of uncertainties. In particular, the reproducibility of the laser shots is considered.

International audienceWe present experimental and numerical results on the formation of a controlled plasma density gradient in front of a solid target irradiated with a subpicosecond, moderate intensity laser pulse. Interferometry with femtosecond probe is used to map the temporal evolution of the spatial density distribution of the generated plasma. Experimental results are found to be in good agreement with 1D1/2 hydrodynamic simulations. Moreover, these numerical simulations enable us to determine the impact of such a heating beam on the target rear surface and to correlate the plasma gradient that can be produced on the illuminated surface with the position of the shock wave in the bulk

Fast electron transport in matter is a key issue for assessing the feasibility of fast ignition; however several important points are not clear yet. Therefore we realized an experiment with ultra-intense lasers ( 6 10 19 W cm −2 ) studying transport in metallic (Al) and insulating (CH) foil targets. The dynamics of fast electron propagation versus target thickness was investigated by optical selfemission from targets rear side. In Al targets we distinguished two-components in the fast electron population: moderately relativistic electrons and a highly collimated micro-bunched relativistic tail. A large ohmic heating at the rear of the thinner targets was observed due to the background return current. In CH, optical emission is mainly due to the Cherenkov effect and is much larger than in Al. We also observed that in insulators the fast-electron beam undergoes strong filamentation and the number of filaments increases with thickness. This behaviour was attributed to an ionization front instability.

International audienceA new method for accelerating proton beams, based on the use of intense and short laser pulses, is presented. It is shown that by focusing an ultrashort laser pulse onto a thin foil target, a proton beam with energy up to tens of MeV is produced. Due to the original properties of these beams unexplored fields in science will be discovered. In addition, this compact and low cost approach would probably be of great interest for medical applications

International audienceWe present here results obtained in an experiment carried out using the CPA beam of the "Salle Jaune" laser system at Laboratoire d'Optique Appliquée (LOA). The generation of high energy electrons and protons escaping from the plasma has been investigated in the interaction of a 2 J, 30 fs laser with CH or metallic foils. The energy and angular distributions of the supra-thermal electrons produced with different targets are characterized by using both an electron spectrometer and bremsstrahlung induced ($\gamma $,n) reactions. We measured simultaneously the number of energetic protons produced using (p,n) reactions. A correlation between the electrons and the protons production is observed together with a dependence of the number of supra-thermal electrons on the atomic number of the target element

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