Electron–Ion Impact Energy Transfer in Nanoplasmas of Coulomb Exploding Clusters

Novel features of analysis and control of nanoplasma dynamics are manifested in elemental and molecular clusters irradiated by a near-infrared intense ultraintense laser pulse, where the laser energy pumped to the nanoplasma electrons is transferred to the cluster ions by Coulomb explosion (CE) and by electron–ion impact mechanisms. The contribution of the electron–ion impact was studied by a microscopic model, together with molecular dynamics simulations of the electron–ion kinetic energy transfer in the course of the electron–ion collision events. The simulations were performed for ionic (He⁺)_N, (Ne⁺)_N, and (Ne^4 +)_N clusters containing weakly charged ions, as well as for (H⁺)_N and (He^2 +)_N clusters consisting of bare nuclei and electrons. The clusters were subjected to femtosecond (τ = 30 fs) laser pulses with peak intensities of I_M = 10¹⁵–10¹⁷ W cm^− 2. The force F_imp, generated by the electron impact kinetic energy transfer was found to decrease strongly with the exploding cluster radius R, i.e., F_imp ∝ R^− η, with η ~ 4–6. The electron impact energy transferred to the periphery ions of clusters (in the size domain of N = 10⁴–10⁶) made up less than 2.5% of the maximal ion energy. The laser energy transfer to the nanoplasma involves the dominating contribution of the Coulomb energy and a minor contribution of the electron impact, with the cluster expansion and decay being governed by the CE mechanism.