Hot nanoplasmas from intense laser irradiation of argon clusters

Argon ions with charge states of at least up to q = 9 are produced with 10(14) W cm(-2), 30 ps laser light pulses at 1064 nm from neutral Ar, clusters, whereas only Ar3+ can be produced from monomers. Irradiation of cluster targets leads to ions with remarkably high kinetic energies exceeding 4.8 keV, depending on the ion charge state. The experimental results are understood in terms of cluster-sized nanoplasmas with internal electron temperatures of approximately 7 x 10(6) K which are heated by collisional electron-ion absorption. From these thermalized superdense nanoplasmas highly charged ions are ejected isotropically with the corresponding ion sound velocity. A simple Coulomb explosion model cannot account for the observed ion energies.