Powerful nanosecond laser-plasma processes are explored to generate discharge currents of a few 100 kA in coil targets, yielding magnetostatic fields (B-fields) in excess of 0.5 kT. The quasi-static currents are provided from hot electron ejection from the laser-irradiated surface. According to our model, which describes the evolution of the discharge current, the major control parameter is the laser irradiance $I_{\text{las}}{\lambda }_{\text{las}}^2$ . The space-time evolution of the B-fields is experimentally characterized by high-frequency bandwidth B-dot probes and proton-deflectometry measurements. The magnetic pulses, of ns-scale, are long enough to magnetize secondary targets through resistive diffusion. We applied it in experiments of laser-generated relativistic electron transport through solid dielectric targets, yielding an unprecedented 5-fold enhancement of the energy-density flux at 60 μm depth, compared to unmagnetized transport conditions. These studies pave the ground for magnetized high-energy density physics investigations, related to laser-generated secondary sources of radiation and/or high-energy particles and their transport, to high-gain fusion energy schemes, and to laboratory astrophysics.

Computational fluid dynamics simulations are performed to design gas nozzles, associated with a 1000 bars backing pressure system, capable of generating supersonic gas jet targets with densities close to the critical density for 1053 nm laser radiation (10²¹ cm⁻³). Such targets should be suitable for laser-driven ion acceleration at a high repetition rate. The simulation results are compared to the density profiles measured by interferometry, and characterization of the gas jet dynamics is performed using strioscopy. Proton beams with maximum energies up to 2 MeV have been produced from diatomic hydrogen gas jet targets in a first experiment.

For most laser-driven ion acceleration applications, a well-characterized intense ion beam with a low divergence and a controllable energy spectrum produced at a high repetition rate is needed. Gas-jet targets have given promising results in simulations, and they have several technical advantages for high-repetition-rate lasers. In this work, we report on proton acceleration to energies up to 6 MeV using a supersonic H₂ gas-jet target at the LULI PICO2000 laser facility. The experimental results are compared with the plasma hydrodynamics and the particle-in-cell simulations to identify the acceleration mechanisms at play.

Strong electromagnetic pulses (EMPs) are generated from intense laser interactions with solid-density targets and can be guided by the target geometry, specifically through conductive connections to the ground. We present an experimental characterization by time- and spatial-resolved proton deflectometry of guided electromagnetic discharge pulses along wires including a coil, driven by 0.5 ps, 50 J, 10¹⁹ W/cm² laser pulses. Proton-deflectometry allows us to time-resolve first the EMP due to the laser-driven target charging and then the return EMP from the ground through the conductive target stalk. Both EMPs have a typical duration of tens of ps and correspond to currents in the kA-range with electric-field amplitudes of multiple GV/m. The sub-mm coil in the target rod creates lensing effects on probing protons due to both magnetic- and electric-field contributions. This way, protons of the 10 MeV-energy range are focused over cm-scale distances. Experimental results are supported by analytical modeling and high-resolution numerical particle-in-cell simulations, unraveling the likely presence of a surface plasma, in which parameters define the discharge pulse dispersion in the non-linear propagation regime.

Ion acceleration from gaseous targets driven by relativistic-intensity lasers was demonstrated as early as the late 1990s, yet most of the experiments conducted to date have involved picosecond-duration, Nd:glass lasers operating at low repetition rate. Here, we present measurements on the interaction of ultraintense $(\approx {10}^{20}\mathrm{W}{\mathrm{cm}}^{-2}, 1 \mathrm{PW})$, ultrashort $(\approx 70\mathrm{fs})$ Ti:Sa laser pulses with near-critical $(\approx {10}^{20}{\mathrm{cm}}^{-3})$ helium gas jets, a debris-free targetry with the potential for future compatibility with high $(\approx 1 \mathrm{Hz})$ repetition rate operation. We provide evidence of $\alpha$ particles being forward accelerated up to $\approx 2.7\text{−}\mathrm{MeV}$ energy with a total flux of $\approx {10}^{11}{\mathrm{sr}}^{-1}$ as integrated over $>0.1\text{−}\mathrm{MeV}$ energies and detected within a $0.5\text{−}\mathrm{mrad}$ solid angle. We also report on on-axis emission of relativistic electrons with an exponentially decaying spectrum characterized by a $\approx 10\text{−}\mathrm{MeV}$ slope, i.e., five times larger than the standard ponderomotive scaling. The total charge of these electrons with energy above 2 MeV is estimated to be of $\approx 1\mathrm{nC}$, corresponding to $\approx 0.1\%$ of the laser drive energy. In addition, we observe the formation of a plasma channel, extending longitudinally across the gas density maximum and expanding radially with time. These results are well captured by large-scale particle-in-cell simulations, which reveal that the detected fast ions most likely originate from reflection off the rapidly expanding channel walls. The latter process is predicted to yield ion energies in the MeV range, which compare well with the measurements. Finally, direct laser acceleration is shown to be the dominant mechanism behind the observed electron energization.

The double laser pulse approach to relativistic electron beam (REB) collimation in solid targets has been investigated at the LULI-ELFIE facility. In this scheme two collinear laser pulses are focused onto a solid target with a given intensity ratio and time delay to generate REBs. The magnetic field generated by the first laser-driven REB is used to guide the REB generated by a second delayed laser pulse. We show how electron beam collimation can be controlled by properly adjusting the ratio of focus size and the delay time between the two pulses. We found that the maximum of electron beam collimation is clearly dependent on the laser focal spot size ratio and related to the magnetic field dynamics. Cu-K_α and CTR imaging diagnostics were implemented to evaluate the collimation effects on the respectively low energy (≤100 keV) and high energy (≥MeV) components of the REB.