High flux of relativistic electrons produced in femtosecond laser-thin foil target interactions: characterization with nuclear techniques.

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.

Study of ultraintense laser-produced fast-electron propagation and filamentation in insulator and metal foil targets by optical emission diagnostics.

The transport of an intense electron beam produced by ultrahigh intensity laser pulses through metals and insulators has been studied by high resolution imaging of the optical emission from the targets. In metals, the emission is mainly due to coherent transition radiation, while in plastic, it is due to the Cerenkov effect and it is orders of magnitude larger. It is also observed that in the case of insulators the fast-electron beam undergoes strong filamentation and the number of filaments increases with the target thickness. This filamented behavior in insulators is due to the instability of the ionization front related to the electric field ionization process. The filamentary structures characteristic growth rate and characteristic transversal scale are in agreement with analytical predictions.

Ultraintense laser-produced fast-electron propagation in gas jets.

We study the propagation of fast electrons in a gas at different densities. A large relativistic electron current is produced by focusing a short-pulse ultrahigh-intensity laser on a metallic target. It then propagates in a gas jet placed behind the foil. Shadowgraphy in the gas shows an electron cloud moving at sub-relativistic average velocities. The experiment shows (i) the essential role of the density of background material for allowing propagation of fast electrons, (ii) the importance of the ionization phase which produces free electrons available for the return current, and (iii) the effect of electrostatic fields on fast-electron propagation.

Ultralow emittance, multi-MeV proton beams from a laser virtual-cathode plasma accelerator.

The laminarity of high-current multi-MeV proton beams produced by irradiating thin metallic foils with ultraintense lasers has been measured. For proton energies >10 MeV, the transverse and longitudinal emittance are, respectively, <0.004 mm mrad and <10(-4) eV s, i.e., at least 100-fold and may be as much as 10(4)-fold better than conventional accelerator beams. The fast acceleration being electrostatic from an initially cold surface, only collisions with the accelerating fast electrons appear to limit the beam laminarity. The ion beam source size is measured to be <15 microm (FWHM) for proton energies >10 MeV.