Excitation of heavy metal clusters by strong fs laser pulses

The excitation of neutral platinum and lead clusters by intense femtosecond laser pulses is studied by time-of-flight spectroscopy. Clusters are completely destroyed when interacting in the high intensity region of the laser focus. Moreover, highly charged atomic ions with up to 20 charges are detected under special pulse conditions. The atomic ion distribution shows a pronounced dependence on the chosen pulse width, suggesting that multi-plasmon excitations are responsible for the high charge states measured. The Coulomb explosion of a metal sphere is simulated under tunneling ionisation conditions. The calculated optical response of such a cluster within the framework of the random phase approximation agrees well with the experimental observations.