The interactions of ultra-short high-intensity laser pulses with large molecules and clusters: Experimental and computational studies

Recent experimental and computational studies on intense short-pulse-laser interactions with small objects such as molecules (C-60) and clusters are r eviewed. An anisotropic Coulomb explosion of C-60 was observed, on irradiat ion by a high-intensity laser pulse (1x10(16) W/cm(2)). The energy distribu tions of Cq+ ions (q=1-4) (distributed over 1 keV) generated from the explo sion process were characterized, with their dependence on laser polarizatio n. These results are qualitatively explained by classical molecular-dynamic s simulation. It was clearly established that the crucial process for the a nisotropic Coulomb explosion is not electron impact ionization, but cascade hopping of electrons. An analytical model and three-dimensional particle s imulations of intense laser interaction with a cluster of overdense plasma are presented. When the laser intensity is above a critical value, it blows off all electrons from the cluster and forms a non-neutral ion cloud. Duri ng the Coulomb explosion of the ion cloud, ions acquire energy. Ion energy spectra are discussed in detail for different densities and sizes of cluste rs with various laser intensities. It is shown that ultra-fast ions are pro duced for relatively large clusters, and that the ion energy reaches to thr ee times greater than the maximum electrostatic potential energy of the ion cloud. The laser-driven Coulomb explosion of a cluster may provide a new h igh-energy ion source. (C) 2001 American Institute of Physics.