Continuum-continuum Autler-Townes splitting in calcium

Abstract

Strong-field ionization of two-electron atoms can result in scenarios in which the electron-electron correlation plays an important role. It was recently suggested that a splitting similar to the Autler-Townes effect would occur when two ionization continua are resonantly coupled in two-electron atoms. This is obviously at variance with the case of one electron atoms where coupling between continua does not induce oscillations but instead leads to exponential decay of one continuum into another. The special case considered by Grobe and Eberly is that of a strong radiation field resonantly coupling two ionic states. Formally, the states which are coupled are continuum states (two-electron states in which one electron is in a continuum state), but nevertheless the corresponding photoelectron peak is split. Physically, the reason for this is that the electron-electron interaction transfers the energy shift of the core electron to the outgoing electron and has been dubbed {open_quotes}coherence transfer{close_quotes} by Ref.