Direct Measurement of Oscillations between Degenerate Two-Electron Bound-State Configurations in a Rapidly Autoionizing System

In this paper we report a direct observation of the oscillation between bound-state configurations in a rapidly autoionizing system. Calcium atoms were excited to a pure 4p3/2nd two-electron configuration using a 500-fsec laser pulse. The initial 4p3/2nd doubly excited state is energy degenerate with the 4p1/2n\u27d states and several continuum channels. Because of the short-pulse excitation, the initial state of the atom is not an energy eigenstate, but a nonstationary wave packet. As a result, oscillations between the two bound configurations were produced. These oscillations were measured by scanning the timing of a second 500-fsec laser pulse tuned to drive the 4p1/2n\u27d ionic state back down to the 4sn\u27d singly excited configuration, which was subsequently detected using selective field ionization. A simple theoretical model was used to model the experimental results and produced good agreement with the data