Frequencies, times, and forces in the dynamics of Na clusters

Laser excitation of metal clusters depends on various parameters such as fr equency, intensity, and pulse time. We give here an overview of relevant ti me scales and forces for the example of Na clusters. Variation of laser int ensity is studied in connection with second harmonic generation. We see a r ather sudden transition from a perturbative regime at low intensities to a field-dominated regime for larger intensities. We use the non-linearized ti me-dependent local density approximation (TDLDA), together with a local pse udopotential for the interaction of the valence electrons with the ions. Ex plicit ionic motion is taken into account in one test case where we demonst rate the importance of ionic effects for the detailed time evolution at tim es larger than 100 fs.