Intensity-dependent characteristics of a picosecond laser-produced Cu plasma

The interaction of a I ps laser pulse of moderate contrast ratio (similar to 10(4)) with a Cu target is investigated at laser intensities I of up to 3 x 10(16) W cm(-2) with the use of corpuscular, x-ray and optical diagnostics. Intensity-dependent characteristics of ion and x-ray emission as well as reflectivity, electron temperature and average charge state of plasma produced by the laser pulse are presented and discussed. It is found that (a) the specular reflectivity dependence on intensity for a moderate-contrast ultrashort (less than or equal to 1 ps) pulse is qualitatively and quantitatively different from that for a high-contrast ultrashort pulse; (b) the scaling laws for parameters of thermal ions are essentially different from those for fast ions; (c) the soft x-ray yield scales as I-alpha with alpha approximate to 2-2.5 in the intensity range 10(14)-3 x 10(16) W cm(-2); and (d) electron temperature scales as I-0.44 at 10(15) < I < 3 x 10(16) W cm(-2).