Two-photon double-ionization of polyelectronic atoms with a virtual sequential model*

Pump-probe experiments with new XUV sources [1] permit to observe correlated electron dynamics with attosecond resolution. The quantitative description of two-photon double ionization (2PDI) dynamics in these experiments is numerically expensive [2,3]. Still, a virtual sequential model (VSM) with only single-ionization intermediate states and no final-state interaction can capture qualitative aspects of this process even below the sequential regime [4]. In this work, we extend the VSM to finite pulses [5] and polyelectronic atoms. The photoionization cross section of the ground state and of the intermediate ionic states are computed ab initio with the NewStock close-coupling code. This model includes the contribution from final autoionizing states as well as finite-pulse effects. The joint energy distribution for the 2PDI of helium compares well with available results in the literature for both single and sequences of multiple ultrashort pulses. Preliminary results for the application of this approach to the neon atom will be presented. 

[1] Duris et al, Nat. Phot. 14, 30 (2020); Saito et al, Optica 6, 1542 (2019).

[2] Feist et al, PRA 77, 043420 (2008).

[3] Palacios et al, PRA 79, 033402 (2009).

[4] Horner et al., PRA 76, 030701(R) (2007).

[5] Jimenez et al, PRA 93, 023429 (2016).