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 $(C60)$ and clusters are reviewed. An anisotropic Coulomb explosion of $C60$ was observed, on irradiation by a high-intensity laser pulse $(1×1016 W/cm2).$ The energy distributions of $Cq+$ ions $(q=1–4)$ (distributed over 1 keV) generated from the explosion process were characterized, with their dependence on laser polarization. These results are qualitatively explained by classical molecular-dynamics simulation. It was clearly established that the crucial process for the anisotropic Coulomb explosion is not electron impact ionization, but cascade hopping of electrons. An analytical model and three-dimensional particle simulations 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. During the Coulomb explosion of the ion cloud, ions acquire energy. Ion energy spectra are discussed in detail for different densities and sizes of clusters with various laser intensities. It is shown that ultra-fast ions are produced for relatively large clusters, and that the ion energy reaches to three times greater than the maximum electrostatic potential energy of the ion cloud. The laser-driven Coulomb explosion of a cluster may provide a new high-energy ion source.