Boosting laser-ion acceleration with multi-picosecond pulses

Using one of the world most powerful laser facility, we demonstrate for the rst time that high-contrast multi-picosecond pulses are advantageous for proton acceleration. By extending the pulse duration from 1.5 to 6 ps with xed laser intensity of 10^18 W cm^−2, the maximum proton energy is improved more than twice (from 13 to 33 MeV). At the same time, laser-energy conversion e ciency into the MeV protons is enhanced with an order of magnitude, achieving 5% for protons above 6 MeV with the 6 ps pulse duration. The proton energies observed are discussed using a plasma expansion model newly developed that takes the electron temperature evolution beyond the ponderomotive energy in the over picoseconds interaction into account. The present results are quite encouraging for realizing ion-driven fast ignition and novel ion beamlines

Ultrahigh-contrast kilojoule-class petawatt LFEX laser using a plasma mirror

Laser pulse contrast exceeding 10^11 was demonstrated on a kilojoule-class petawatt laser for fast ignition experiments (LFEX) laser system [J. Phys. IV France 133, 81 (2006)] by implementing a 2 in. plasma mirror. Laser beams of up to 1.2 kJ striking the plasma mirror with a pulse duration of 1.5 ps were reflected and focused onto a target without significant distortions in the focal spot. Transmitted light from the plasma mirror reveals that it has a high reflectivity 2 ps before the main peak. The estimated laser pulse contrast at the target was 10^11 at 1 ns before the main peak. No preformed plasma was observed with optical interferometry diagnostics, but in the experiment without a plasma mirror a preplasma was clearly observed. The energetic proton was generated from a 0.1μm thick CH film showing excellent pulse contrast. This technique constitutes a promising method to enhance the LFEX laser system performance in fast ignition experiments