Two-photon double ionization with finite pulses: Application of the virtual sequential model to helium

As a step toward the full ab initio description of two-photon double ionization processes, we present finite-pulse version virtual-sequential model for polyelectronic atoms. The relies on single scattering states both neutral and ionized target system. proof principle benchmark, is applied to helium atom using newstock atomic photoionization code. results angularly integrated observables, which are in excellent agreement with existing time-dependent Schr\"odinger equation (TDSE) simulations, show how able capture role electron correlation nonsequential regime, influence autoionizing sequential at comparatively modest computational cost. also reproduces two-particle interference ultrashort pulses, within reach current experimental technologies. Furthermore, shows modulation joint energy distribution vicinity states, can be probed extreme-ultraviolet pulses duration much longer than characteristic lifetime resonance. formalism discussed here applies atoms molecules, thus opening window these more complex systems.