[en] The frequency doubled laser pulses from the T3 laser system at the Center for Ultrafast Optical Science of the University Michigan (with energy up to 1 J, a pulse duration of 400 fs, the wavelength is 0.53 μm and the maximum intensity is 2.7*10¹⁹ W/cm²) has been used to measure the light transmitted through thin metal targets. The intensity contrast ratio of the laser pulse was better than 10^-9 which is low enough to suggest the interaction with solid density plasma without pre-plasma. We observed the transmittance of the laser pulse through the aluminum foil with thickness up to 4 μm and found that this radiation is polarized and centered at 0.53 μm. We found that for 0.8 μm thick foils the transmission was anomalously high (about 10^-2%) and can't be explained by the skin effect of the relativistic pulse. (authors)

[en] The complex dynamical behavior of the electron sheath in laser driven ion acceleration leads to variations in ion beam pointing and ion energy modulation. These processes are derived from high resolution particle spectroscopy and 2D-PIC simulations. The phenomena arise from ion source movement if laser irradiation occurs at oblique incidence. Different laser absorption processes act in dependence on laser parameter which determines ion acceleration. (authors)

[en] In the interaction of a 30 fs, 40 TW Ti:sapphire Hercules laser focused to the intensity of 10¹⁹ W/cm² onto a supersonic He gas jet, we observed quasi-monoenergetic electron beams with energy up to 300 MeV and an angular divergence of 10 mrad. We found that the initial plasma density significantly affects the resultant electron beam. For plasma densities ranging between 2*10¹⁹ to 3.5*10¹⁹ cm^-3, quasi-monoenergetic electrons with energies from 80 to 160 MeV and a total charge of about 0.5 nC were produced. Lower plasma densities around 1.5*10¹⁹ cm^-3 produced quasi-monoenergetic electron beams with higher energy, up to (320 ± 50) MeV, but with a decrease of the total charge to about 5 pC. Characterization of the electron beam in terms of the electron's maximum energy, beam divergence and pointing stability is presented. The performed 2-dimensional PIC (particle-in-cell) simulations show the evolution of the laser pulse in the plasma, electron injection, and the specifics of electron acceleration. (authors)

[en] We present here results obtained in an experiment carried out using the CPA beam of the laser system at the laboratory of applied optics (LOA) in Palaiseau (France). 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 (γ,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. Preliminary results concerning the integrated number of (γ,n) reactions are 5700 ± 500 reactions with Al target, 46800 ± 1500 with Cu target and 90000 ± 1900 with Au target. Comparatively, we measure 30000 ± 1400 (γ,n) with 10 μm polyethylene target. The number of (γ,n) reactions increases with the atomic number Z of 10 μm metallic targets. For the 10 μm Al target the number of (p,n) reactions is about 20-40% of (γ,n) ones for all shots

[en] Data from a pinhole camera and a transmission grating spectrograph are used in multi-TW laser irradiance of thin metal films to assess the maximum laser spot size and to show tenths of a percent conversion of laser light to K-, L-, and M-band X rays. The distribution of target debris, an operational issue for the survivability of an unshielded parabola in a large laser system, is revealed by X-ray fluorescence measurements of witness samples. At the 25-J, 30-TW level, we find little evidence of damage to the f/3 parabola with an angle of incidence on target greater than 22. (authors)

[en] Quality of an ion beam is one of the critical factors in intense-laser ion beam generation. A purpose of this study is the suppression of transverse proton divergence by a controlled electron cloud in laser-foil interactions. In this study, the foil target has a hole at the opposite side of the laser illumination. The electrons accelerated by an intense laser are limited in transverse by a neutral plasma at a protuberant part. Therefore the protons are accelerated and also controlled transversely by the electron cloud structure. In our 2.5-dimensional Particle-in-Cell simulations we demonstrate that the transverse shape of the electron cloud is well controlled and the collimated proton beam is generated successfully in the target with the hole. (authors)

[en] High-intensity (>10¹⁹ W cm^-2) laser-plasma interactions have been shown to produce large quantities of protons with energies up to several tens of MeV. A range of laser-driven proton-induced reactions in copper have been investigated and the observed reactions quantified. The energy spectrum of the accelerated protons was determined from the reactions in a single thin copper foil and found to be in agreement with that deduced from (p,n) reactions measured in a stack of copper foils. The potential applications of this diagnostic technique are discussed

[en] In this paper we report on inner ionization of Xe_n clusters (n = 55 - 2171) in ultra-intense Gaussian laser fields (peak intensity I = 10¹⁵ - 10²⁰ Wcm^-2, pulse width τ = 25 fs, frequency 0.35 fs^-1). The cluster inner ionization process is induced by the barrier suppression ionization (BSI) mechanism and by electron impact ionization (EII), which occurs sequentially with the BSI. We address electron impact ionization of clusters, which pertains to inelastic reactive processes of the high-energy (100 eV - 1 keV per electron) nano-plasma. We utilized experimental data for the energy dependence of the electron impact ionization cross-sections of Xe^j+ (j = 1 - 10) ions, which were fit by an empirical three-parameter Lotz-type equation, to explore EII in clusters by molecular dynamics simulations. Information was obtained on the yields and time-resolved dynamics of the EII levels (i.e., number n(imp) of electrons per cluster atom) in the Xe_n clusters and their dependence on the laser intensity and cluster size. The relative long-time (t = 90 fs) yields for EII, n(imp)/n(ii) (where n(ii) is the total inner ionization yield) are rather low and increase with decreasing the laser intensity. In the intensity range I equals 10¹⁵ - 10¹⁶ Wcm^-2, n(imp)/n(ii) = 0.21 for n = 2171 and n(imp)/n(ii) equals 0.09 - 0.14 for n = 459, while for I = 10¹⁸ - 10²⁰ Wcm^-2, n(imp)/ n(ii) equals 0.01 - 0.05. The difference Δn(imp) between the EII yield at long time and at the termination of the laser pulse reflects on ionization dynamics by the nano-plasma when the laser pulse is switched off. For Xe₂₁₇₁ in the lower intensity domain, Δn(imp) = 0.9 at I = 10¹⁵ Wcm^-2 and Δn(imp) = 0.4 at 10¹⁶ Wcm^-2, reflecting on EII by the persistent nano-plasma under 'laser free' conditions, while in the higher intensity domain of I = 10¹⁷ - 10¹⁸ Wcm^-2, Δn(imp) is negligibly small due to the depletion of the transient nano-plasma. (authors)

[en] High energetic ion generation from thin foil targets irradiated by 30 fs laser pulses at intensity 10²⁰W/cm² has been studied as a function of various concaves. We have demonstrated an increased acceleration and higher ion energies for the targets with triangle concave by using particle-in-cell (PIC) simulations. The optimum target plasma conditions for the maximum ion acceleration are found. Mechanism of fast (multi-MeV) ion acceleration in the rear of the targets with triangle concaves is analyzed. (author)

[en] The general context of this study is the Inertial Confinement for thermonuclear controlled fusion and, more precisely, the Fast Igniter (FI). In this context the knowledge of the generation and transport of fast electrons is crucial. This thesis is an experimental study of the generation and transport of fast electrons in the interaction of a high intensity laser (≥ 10¹⁹ W/cm²) with a solid target. The main diagnostic used here is the transition radiation. This radiation depends on the electrons which produce it and thus it gives important information on the electrons: energy, temperature, propagation geometry, etc. The spectral, temporal and spatial analysis permitted to put in evidence the acceleration of periodic electron bunches which, in this case, emit a Coherent Transition Radiation (CTR). During this thesis we have developed some theoretical models in order to explain the experimental results. We find this way two kinds of electron bunches, emitted either at the laser frequency (ω₀), either at the double of this frequency (2ω₀), involving several acceleration mechanisms: vacuum heating / resonance absorption and Lorentz force, respectively. These bunches are also observed in the PIC (particle-in-cell) simulations. The electron temperature is of about 2 MeV in our experimental conditions. The electrons are emitted starting from a point source (which is the laser focal spot) and then propagate in a ballistic way through the target. In some cases they can be re-injected in the target by the electrostatic field from the target edges. This diagnostic is only sensitive to the coherent relativistic electrons, which explains the weak total energy that they contain (about a few mJ). The CTR signal emitted by those fast electrons is largely dominating the signal emitted by the less energetic electrons, even if they contain the major part of the energy (about 1 J). (author)