Cluster ionization via two-plasmon excitation - art. no. 033202

We calculate the two-photon ionization of clusters for photon energies near the surface plasmon resonance. The plasmon is described in a schematic jel lium-RPA model assuming a separable residual interaction between electrons determined so that the plasmon energy is reproduced. The ionization rate of a double plasmon excitation is calculated perturbatively. In Na-93(+) clus ters we find an ionization rate of the order of at most 0.05-0.10 fs(-1). T his rate is used to determine the ionization probability in an external fie ld in terms of the number of absorbed photon pairs and the duration of the field. We discuss the dependence of the results on the choice of our empiri cal separable force. The number of emitted electrons per pair of absorbed p hotons is found to be small, in the range 10(-5) to 10(-3).