For most applications of laser driven ion beams, a well-characterized high repetition rate intense ion beam with low divergence and a controllable energy spectrum is needed. High power laser-solid targets interactions are usually used, in which the main acceleration mechanism is the so-called Target Normal Sheath Acceleration (TNSA). Changing solid targets for overcritical gas jet targets has given interesting results in theoretical simulations and these later have several technical advantages for high repetition rate lasers. In this work protons and helium ions are accelerated from a near-critical supersonic gas jet. The production of such targets is very challenging for near infrared lasers. We present recent results concerning the design and characterization of supersonic gas nozzles able to deliver such high densities and the first results obtained during the first experiment on PICO2000 facility at LULI. We succeeded to accelerate ions up to several MeV with a H<sub>2</sub> and He gas jet target. The number of accelerated ions is comparable to the one usually obtained with solid targets.
Due to their extremely high damage threshold, plasmas can sustain much higher light intensities than conventional solid state optical materials. Because of this, lately much attention has been devoted to the possibility of using parametric instabilities in plasmas to generate very intense light pulses in a low-cost way. Although short-pulse amplification based on the Raman approach has been successful and goes back a long time, it is shown that using Brillouin in the so called strong-coupling regime (sc-SBS) has several advantages and is very well suited to amplify and compress laser seed pulses on short distances to very high intensities. We present here recent multi-dimensional kinetic simulations that show the feasibility of achieving amplified light pulses of up to 10<sup>18</sup>W/cm<sup>2</sup>. Contrary to what was traditionally thought, this scheme is able to amplify pulses of extremely short duration. Although seed amplification via sc-SBS has already been shown experimentally, these results suggest further experimental exploration, in order to improve the energy transfer.
Energy Energy transfer between a long (3-10 ps) "pump" pulse and a short (400 fs) "seed" one, both at a wavelength of 1.057μm
quasi counterpropagating in an underdense preformed plasma and produced from the ionization of a gas jet, was
observed. Numerical simulations reveal that the energy transfer is due to the coupling involving ion acoustic waves
excited in the Stimulated Brillouin Backscattering in the strong coupling regime. The plasma characteristics were
tailored using a high-energy ionization laser beam and the plasma density was controlled using a Thomson scattering
diagnostic. The energy exchange was observed for different gas (ion) types, pressures (plasma densities), polarization
and intensities of the interacting beams.