Microscopic and hydrodynamic impact energy transfer from nanoplasma electrons to ions in exploding clusters

Nanoplasma energetics and dynamics are manifested in elemental and molecular clusters irradiated by a near-infrared intense laser pulse, in which the laser energy pumped to the nanoplasma electrons is transferred to the cluster ions by Coulomb explosion and by electron-ion impact processes. The attosecond electron-ion impact events within a nanoplasma were studied by scaled electron and ion dynamics simulations of the kinetic energy transfer between electrons and ions in the course of the electron-ion collision events. The simulations were performed for electron-ion repulsive collisions in clusters containing N ions and nanoplasma electrons, as well as for electron-ion Coulomb collisions in clusters consisting of bare nuclei and nanoplasma electrons. The clusters were driven by femtosecond laser pulses with peak intensities of I_M = 10¹⁵–10¹⁷ W cm⁻². The electron impact energy transferred to the periphery ions of large clusters made up for less than 4% of the maximal ion energy, demonstrating the dominating contribution of the Coulomb energy. The hydrodynamic pressure energies were calculated by using the structural and energetic parameters during the cluster expansion. The convergence between the macroscopic hydrodynamic model and the microscopic electron-ion impact model may be exhibited only in electron-rich nanoplasmas.