Integrity of dressed states in multiphoton ionisation

Abstract

The dressed eigenstates of an atom interacting with a near-resonant radiation field are used to study the dynamics and final-state photoelectron spectra of resonant two-photon ionisation for arbitrary initial conditions and detunings. The authors find that under some circumstances (and particularly for intense fields) the dressed states preserve their integrity whilst decaying as distinguishable states, leading to AC Stark-split photoelectron energy spectra. In general, however, there exists an off-diagonal coupling between dressed states via the continuum so that each dressed state cannot decay independently of the existence of the other. This can modify lowest order expectations, particularly for weak fields and can entirely alter final-state spectra.