Nanoplasma dynamics in Xe clusters driven by ultraintense laser fields

We present a theoretical and computational study of the properties and the response of the nanoplasma and of outer ionization in Xe_n clusters (n = 55-2171, initial cluster radius R₀ = 8.7-31.0 Å) driven by ultraintense near-infrared laser fields (peak intensity I_M = 10 ¹⁵-10²⁰ Wcm^-2, temporal pulse length τ= 10-100 fs, and frequency ν= 0.35 fs^-1). The positively charged high-energy nanoplasma produced by inner ionization nearly follows the oscillations of the fs laser pulse and can either be persistent (at lower intensities of I_M = 10¹⁵-10¹⁶ Wcm^-2 and/or for larger cluster sizes, where the electron energy distribution is nearly thermal) or transient (at higher intensities of I_M = 10 ¹⁸-10²⁰ Wcm^-2 and/or for smaller cluster sizes). 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. The electrostatic model was further utilized for estimates of the laser intensity and pulse width dependence of the border radius R₀ ^(I) for the attainment of complete outer ionization at, while at R₀ > R₀ ^(I) a persistent nanoplasma prevails. R₀ ^(I) establishes an interrelationship between electron dynamics and nuclear Coulomb explosion dynamics in ultraintense laser-cluster interactions.