Possible ionization ignition in laser-driven clusters

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Abstract
We use classical trajectory Monte Carlo (CTMC) simulations to study the ionization of small rare gas clusters in short pulse, high intensity laser fields. We calculate, for a cluster of 25 neon atoms, the ionization stage reached and the average kinetic energy of the ionized electrons as functions of time and peak laser intensity. The CTMC calculations mimic the results of the much simpler barrier suppression model in the limit of isolated atoms. At solid density our results give much more ionization in the cluster than that predicted by the barrrier suppression model. We find that when the laser intensity reaches a threshold value such that on average one electron is ionized from each atom, the cluster atoms rapidly move to higher ionization stages, approaching NE+8 in a few femtoseconds. This 'ignition' process creates an ultrafast pulse of energetic electrons in the cluster at quite modest laser intensities.

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