Rabi oscillation in few-photon double ionization through doubly excited states

Abstract

We theoretically investigate few-photon double ionization of helium in intense XUV laser fields by numerically solving the time-dependent Schr\"odinger equation. Our results show that the familiar single-ring structure in the joint electron momentum spectra is split into the double-ring and previously unobserved triple-ring structures at some specific photon energies. By tracing the electron population evolution of the corresponding states, we found that the triple-ring structure is induced by the coupled Rabi oscillations among the ground, a singly excited, and a doubly excited states. The intermediate detuning causes the asymmetry of the triple-ring structures, which can be controlled by changing the laser intensity and frequency.