Direct measurement of oscillations between degenerate two-electron bound-state configurations in a rapidly autoionizing system

Abstract

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 ${4p}_{3/2}\mathrm{nd}$ two-electron configuration using a 500-fsec laser pulse. The initial ${4p}_{3/2}\mathrm{nd}$ doubly excited state is energy degenerate with the ${4p}_{1/2}{n}^{\ensuremath{'}}d$ 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 ${4p}_{1/2}{n}^{\ensuremath{'}}d$ ionic state back down to the ${4sn}^{\ensuremath{'}}d$ 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.