Generation of hot plasma at solid density by high-contrast ultra-short laser pulses

We have generated a high-density plasma by focusing frequency-doubled Ti-Sa pphire laser pulses at lambda = 395 nm and a duration of 150 fs on flat sol id targets at an intensity of approximate to 10(17) W/cm(2). Using solid Al targets tamped by a thin surface layer of MgO we measured the Al K-shell e mission. The measured resonance lines (Ly(alpha), He-alpha and He-beta) and their Li-like and He-like satellites are extremely broad. In addition, we observed clear center of gravity red shifts of the main lines by using the cold K-alpha line as a reference. The temporal duration of the K-shell emis sion, measured by an X-ray streak camera, is approximate to 2.5 ps. Analysi s of the spectra yields an effective electron temperature of approximate to 300 eV and an electron density of approximate to (7-10) x 10(23) cm(-3). A very weak emission of cold Al K-alpha indicates a low level of energy depo sited by fast electrons in the solid. Essential for achieving these results is the suppression of early time expansion of the Al target by using both, a high-contrast laser pulse and a tamped target. (C) 2000 Elsevier Science Ltd. All rights reserved.