Real-time fragmentation dynamics of clusters ionized by intense extreme-ultraviolet pulses

We investigate the fragmentation dynamics of atomic clusters ionized by intense extreme-ultraviolet pulses from a high-order harmonic generation source. It is demonstrated that the transient modification of the trimer fragment yield induced by a weak near-infrared (NIR) probe pulse provides valuable information on the cluster disintegration process. For medium-sized Ar clusters and delays of around 5 ps, we observe a transition from a collective response, where efficient absorption of the NIR laser energy takes place, to a state where the interaction of the probe laser pulse with individual fragments dominates. The cluster disintegration is faster for smaller clusters, in agreement with a simple physical picture taking into account the measured expansion speeds of excited and ionic fragments. For Xe clusters, we find a significantly increased fragmentation time of about 40 ps, attributed to the larger atomic mass and to more efficient electron–ion recombination processes. (paper)