Control of cluster multielectron ionization in ultraintense laser fields

We performed classical molecular dynamics simulations to explore the controllability of the inner ionization process in Xe_n clusters (n = 2-2171), driven by ultraintense infrared Gaussian laser fields (peak intensity I _M = 10¹⁵-10¹⁸ W cm^-2, temporal pulse length τ = 10-100 fs, and frequency ν = 0.35 fs^-1). Controllability of ion charge abundances and of their spatial distributions inside the cluster emerges from the different pulse length dependences of classical barrier suppression ionization (BSI) and of electron impact ionizations (EII), as well as from the time scale of the Coulomb explosion (CE). For large clusters (Xe₂₁₇₁), low intensities (10¹⁵ W cm^-2), and long pulses (τ = 100 fs), EII is the dominating ionization channel, which favors the formation of maximum charged ions (Xe ¹⁰⁺, Xe¹¹⁺) in the cluster center. In contrast, BSI forms an inverse radial charge ordering with the highest charges in the exterior cluster shells. This suggests that the production of the two inverse radial charge distributions with an equal average ion charge can be forced by the choice of multiple pulses with different intensities and pulse lengths. At high intensities (10¹⁷-10¹⁸ W cm^-2), where EII is insignificant and CE sets in much earlier, the BSI radial charge ordering and the enhancement of the ion charges beyond the single-atom limit by the ignition effect is observed only for short pulses.