Clusters in strong external perturbations

Clusters in the strong fields of extremely intense lasers show a much different dynamics. Core electrons can be released and contribute strongly to the process. The detailed description at the fully quantum mechanical level of TDLDA becomes untractable. However, the excitations involved validate classical approaches.

The figure to the right shows the result of a molecular dynamics simulation of electronic and ionic dynamics of Na₄₁⁺ under the influence of strong laser fields [Bel06]. Ionization is drawn as function of laser intensity. One sees a sharp kink at a critical intensity of I = 10¹⁶ W/cm². This threshold value is explained by the fact that the Coulomb force from the laser field at the threshold just equals the binding forces of the core electrons. The increase is due to the core electrons which now start to participate in the dynamics. This view is illustrated by separating the contributions from valence (green line) and core electrons (red line). There is indeed zero emission from core electrons up to I = 10¹⁶ W/cm² and the strong increase above that critical intensity is exclusively due to the contribution from core electrons.

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