Energy and angular distributions of the fast outgoing electron beam induced by the interaction of 1-2 J, 30 fs, 3-20x10<sup>18</sup> W/cm<sup>2</sup> laser with a thin foil or a gas jet target are characterized by using both an electron spectrometer and Bremsstrahlung induced photo-nuclear reactions. The supra-thermic electron beams production was investigated for a solid target versus its thickness and its Z number, and for a gas jet target versus its pressure. Using a polyethylene target and a supersonic Helium gas jet target, we measured, respectively, up to 4x10<sup>8</sup> and 3x10<sup>9</sup> electrons produced per laser pulse, with energies up to, respectively, 60 MeV and 160 MeV. The associated Boltzmann temperature of these electrons is colder for thin foils (9 MeV) than for gas jet (18 MeV). About, respectively 0.06% and 1% of the laser energy has been converted to outgoing electrons with energies above 5 MeV. Such electrons leave the plasma in the laser direction within a cone with an opening angle of, respectively, 2.5° and 8.5°. We discuss the physical processes of electron acceleration. Numerical calculations show a good agreement with the experiments.
A search of Nuclear Excitation by Electron Transition (NEET) in <SUP>235</SUP>U excited in the plasma produced by a 300 mJ, 10 ns laser is presented. Many experimental aspects have been faced to evidence the low rate of NEET excitation of the 76 eV isomeric level in <SUP>235</SUP>U with a plasma temperature T=25 eV. The experimental limit measured for the transition rate for the 76 eV <SUP>235</SUP>U<SUP>m</SUP> state is (lambda) <SUB>N</SUB><2.10<SUP>-5</SUP>s<SUP>-1</SUP>. Several potential upgrades are considered to aim at a measure of the NEET excitation rate in <SUP>235$</SUP>U.
Photo-excitation nuclear reactions induced by the 2J, 30 fs, 4x10<SUP>10</SUP>W/cm<SUP>2</SUP>, 10 Hz LOA laser were optimized with respect to the thickness of the solid target. Using 6 micrometers CH targets, electrons up to 60 MeV have been produced and converted to (gamma) -rays by Bremsstrahlung in a Ta piece. The rate of photo-fission of <SUP>238</SUP>U, as well as photo- excitation nuclear reactions in Cu, Au and C samples have been measured. More than 10<SUP>6</SUP> nuclear reactions were obtained after 60 subsequent laser shots. The high energy electrons are forward focused, within 15 degree(s), as observed from the angular distribution of the activation in Cu. 1% of laser energy was converted to (gamma) -rays with energies higher than 10 MeV.
Frequency doubling a large aperture sub ps, chirped pulse amplified (CPA) 1053 nm beam for laser matter interaction studies was investigated at the Central Laser Facility. Efficiencies > 50 percent were achieved using a 4 mm thick KDP crystal to convert a 140 X 89 mm 700 fs beam. Measurements of the 527 nm beam's focal spot quality when the doubling crystal was driven at high intensities 200 GWcm<SUP>-2</SUP> are presented. Using data from 2 and 4 m thick 25 mm diameter test crystals, the optimum crystal thickness in terms of conversion efficiency is reviewed for 1053 nm CPA systems in the 0.3-3 ps region and options for fourth harmonic production discussed.