ECAMP 15

We study the role of electronic correlations during high harmonic generation (HHG) in multi-electron atoms. Originally viewed as a process involving one single active electron, the influence of multi-electron effects on the HHG spectrum has lately been extensively studied (see e.g. [1, 2]). We quantify the time-dependence of electron-electron correlations on ultrafast time scales using correlation measures from quantum information theory.
By explicitly solving the time-dependent Schrödinger equation with the multi-configurational time-dependent Hartee-Fock (MCTDHF) method [3], we obtain fully correlated results for He, Ne, Be and Mg. Using driving fields adjusted to the ionization potential of each atom, such that the driving occurs in the strong-field regime and double-ionization is negligible, we compare the HHG yields for the different atomic species.
We find prominent features of the influence of correlations on both the tunneling as well as the recombination step. While during tunneling the correlations systematically increase for noble gase atoms (He, Ne), they decrease for alkaline earth atoms (Be, Mg). During recombination we find that the correlated electrons oscillate out of phase relative to each other. Both processes imprint distinct signatures of correlations on the HHG spectrum.

[1] A. D. Shiner et al., Nature Phys 7, 464–467 (2011).
[2] Y. Li et al., Phys. Rev. A 99, 043401 (2019).
[3] T. Sato et al., Phys. Rev. A 94, 023405 (2016).