37 / 2023-04-04 11:24:32

Multi-photon double ionization of helium by ultrashort XUV pulses: probing the role of electron correlations

Multi-photon double ionization,electron correlations,Strong XUV pulses

极端光下的基础物理学 > 极端光下的基础物理学-海报

  Most of the existing studies on multi-photon double ionization (MPDI) of atoms in the XUV regime are restricted to the low-order processes of 1-photon double ionization (1PDI) and 2-photon double ionization (2PDI). Only recently, experimental investigations of higher order processes have became available [1]. We have systematically investigated double ionization by ultrashort XUV pulses by varying the number of absorbed photons (up to 5) and the pulse duration from about 100 attoseconds to 20 femtoseconds by solving the TDSE in its full dimensionality, using a wave-splitting method to make the numerical calculations at long pulse durations feasible [2].



 We have explored the interplay between sequential and non-sequential double ionization for different photon orders and have identified alternative pathways towards double ionization. Most importantly, we find that a path involving a multi-photon two-electron excitation-ionization step followed by a one- or multi-photon ionization of excited He⁺ competes with the direct non-resonant sequential ionization via the ground state of He⁺. Electron correlation effects are shown to be of importance also for sequential processes. This applies also to the two-electron continuum where side-by-side emission with equal energy sharing becomes possible in the sequential regime for long pulses due to Coulomb repulsion. For ultrashort pulses in the attosecond regime MPDI becomes strongly non-sequential with correlation effects in the time domain even in the spectrally sequential regime.