Theory for the ultrafast dynamics of excited clusters: interplay between elementary excitations and atomic structure

We present a theoretical study of the short-time relaxation of clusters in response to ultrafast excitations using femtosecond laser pulses. We analyz e the excitation of different types of clusters (Hg-n, Ag-n, Si-n C-60 and Xe-n) and classify the relaxation dynamics in three different regimes, depe nding on the intensity of the exciting laser pulse. For low-intensity pulses (I < 10(12) W/cm(2)) we determine the time-depende nt structural changes of clusters upon ultrashort ionization and photodetac hment. We also study the laser-induced non-equilibrium fragmentation and me lting of Si-n and C-60 clusters, which occurs for moderate laser intensitie s, as a function of the pulse duration and energy. As an example for the case of high intensities (I > 10(15) W/cm(2)), the ex plosion of clusters under the action of very intense ultrashort laser field s is described.