Optimal control of femtosecond laser-cluster interactions

We present calculations showing that ionization of Xe_N (N=108-1524) clusters by intense femtosecond lasers is governed by two mechanisms that have their origin in molecular and plasma physics, respectively. Optimal-control calculations show that a three-pulse sequence optimizes cluster ionization and involves both enhanced ionization and resonant driving of collective electron oscillations. As a result we can understand how ionization in intense laser fields evolves from small molecules to large clusters