Two-Electron Atoms in Ultra Short, Intense Pulses

Abstract

Although most of multiphoton strong field experiments are performed on multi-electron atoms, it appears that the behavior can be understood in terms of Single Active Electron (SAE) models. Multiple ionization (ejection of as many as ten electrons) is of course a well-established phenomenon¹, above a certain range of intensity. But since (with the exception of one or two cases which are still unclear) the electrons are emitted sequentially, the SAE picture can be said to be valid as well in that case. On the other hand, it is known that 2-electron excitations have played a significant role in the multiphoton excitation and ionization of alkaline earth atoms^2–4. This has happened in experiments with intensities in the range of 10^{9 –} 10¹³ W/cm² where transition probabilities calculated through perturbation theory (including resonance effects) has been capable of providing a good interpretation of the underlying behavior⁴. Thus it can be safely said that multiphoton 2-electron excitation has played an important role in certain atoms, although 2-electron direct ejection remains to be established.