One-dimensional Thomas-Fermi model of atoms, molecules, and small clustersexposed to an intense laser field

We have developed a one-dimensional time-dependent Thomas-Fermi model of at oms, molecules, and small clusters exposed to an intense subpicosecond lase r field. In this model, the dynamics of an electronic cloud is governed by the hydrodynamic equations of motion, whereas the nuclei move in accordance with the Newton equations. The quantum mechanics enters in this approach o nly through the constitutive relation between the pressure and the density, which is derived from the application of Fermi-Dirac statistics to a nonin teracting T = 0 temperature electron gas. The time-independent version of t he model, formulated in terms of the integral equation for the electric pot ential, is also discussed. We present numerical results for diatomic molecu les and small clusters irradiated by the strong laser pulses. In the case o f molecules, we observe the multielectron ionization accompanied by dissoci ation. The kinetic energy defect, understood as a reduction of the energy o f resulting ions in comparison with a simple Coulomb explosion picture, is explained in terms of a screening effect of escaping fragments by the eject ed electrons. For small clusters we fmd that the explosion of the cluster h as a stepwise character; the consecutive layers of atoms are stripped off o ne by one. We observe the highly energetic (as compared with diatomic syste ms) atomic fragments even for relatively low laser intensities and a few at oms clusters. Also, the model predicts the nonuniform energy distribution a mong the same charge state ions and supports the idea of hot electrons gene rated in the cluster via a mechanism of inverse bremsstrahlung. [S1050-2947 (99)02109-5].