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 France133, 81 (2006)10.1051/jp4:2006133016] 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 an optical interferometry diagnostics, but in the experiment without a plasma mirror a preplasma was clearly observed. The energetic proton was generated from a 0.1 μm thick CH film showing excellent pulse contrast. This technique constitutes a promising method to enhance the LFEX laser system performance in fast ignition experiments.