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We present the results of theoretical–computational studies of inter-particle energy transfer caused by elastic electron–ion collisions in expanding (H +) N + electrons and N e 8 + N + electrons nanoplasmas, which are produced from clusters driven by near-infrared femtosecond, intense laser pulses. In these nanoplasmas, the short-range part of the electron–ion interactions is attractive for the H + ions and repulsive for the N e 8 + ions. The electron–ion collision times are ultrashort with τ = 10 - 20 as (attoseconds) for N e 8 + N + electrons nanoplasmas and τ = 10 –50 as for ( H + ) N + electrons nanoplasmas. The collisional inter-particle energy transfers (CIET) are two-directional, occurring either from an electron to an ion or vice versa. The magnitude of the separate energy transfer processes depends on the kinetic energies of both colliding particles as well as on the collision geometry. While our previous studies dealt with periphery ions, the present work considers the collisional energy transfer within the entire clusters, where the relation between electron to ion and ion to electron energy transfers was found to be close to balance, providing on average a low net collisional energy transfer to ions. In the clusters' inner cores this energy transfer presents 2–4% of the final ion energies in the N e 8 + N clusters and less than 1% in the H + N clusters, being lower in the clusters' outer shells. Our findings provide strong evidence for the absence of the so called hydrodynamic expansions and for the dominance of Coulomb interactions in the explosion of the cluster nanoplasmas. [ABSTRACT FROM AUTHOR]

In this paper we present computational and theoretical studies of extreme multielectron ionization in Xen clusters (n = 55-2171, initial cluster radii R0 = 8.7-31.0 Å) driven by ultraintense Gaussian infrared laser fields (peak intensity IM = 1015-1020 W cm-2, temporal pulse length τ = 10-100 fs, and frequency ν = 0.35fs-1). The microscopic approach, which rests on three sequential-parallel processes of inner ionization, nanoplasma formation, and outer ionization, properly describes the high ionization levels (with the formation of {Xeq+}n with q = 5-36), the inner/outer cluster ionization mechanisms, and the nanoplasma response. The cluster size and laser intensity dependence of the inner ionization levels are determined by a complex superposition of laser-induced barrier suppression ionization (BSI), with the contributions of the inner field BSI manifesting ignition enhancement and screening retardation effects, together with electron impact ionization. The positively charged nanoplasma produced by inner ionization reveals intensity-dependent spatial inhomogeneity and spatial anisotropy, and can be either persistent (at lower intensities) or transient (at higher intensities). The nanoplasma is depleted by outer ionization that was semiquantitatively described by the cluster barrier suppression electrostatic model, which accounts for the cluster size, laser intensity, and pulse length dependence of the outer ionization yield. [ABSTRACT FROM AUTHOR]