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

Abstract

We have generated a high-density plasma by focusing frequency-doubled Ti-Sapphire laser pulses at λ=395 nm and a duration of 150 fs on flat solid targets at an intensity of ≈10 17 W/ cm 2 . Using solid Al targets tamped by a thin surface layer of MgO we measured the Al K-shell emission. The measured resonance lines ( Ly α, He α and He β ) 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 α line as a reference. The temporal duration of the K-shell emission, measured by an X-ray streak camera, is ≈2.5 ps. Analysis of the spectra yields an effective electron temperature of ≈300 eV and an electron density of ≈(7–10)×10 23 cm −3 . A very weak emission of cold Al K α indicates a low level of energy deposited 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.