Two-electron dynamics in nonlinear double excitation of helium by intense ultrashort extreme-ultraviolet pulses

摘要

We study multiphoton ionization of He, where the photon energy equals to the transition energy from the ground state to a Rydberg state, aiming to resolve the mechanism of the enhanced double electron excitation through three-photon absorption as observed in a recent experiment [1]. Accurate theoretical photoelectron spectra are shown by solving the time-dependent Schrodinger equation rigorously with the time-dependent hyperspherical method. The peculiar dominance of the three-photon absorption yields over the two-photon yields is confirmed [2].