Photoelectron -- residual-ion entanglement in streaked shake-up ionization of helium

TL;DR

This paper investigates how correlated electron dynamics during helium ionization influence streaked photoelectron spectra, revealing the importance of residual-ion interactions and their dependence on emission direction and energy.

Contribution

It provides ab initio calculations of shake-up ionization in helium, highlighting the role of residual-ion interactions in streaked photoemission delays and their directional dependence.

Findings

Residual-ion interactions significantly affect streaked photoelectron spectra.

Shake-up ionization shows strong direction-dependent effects.

Good agreement with previous experimental and theoretical results.

Abstract

Streaked photoelectron emission spectra access the correlated dynamics of photoelectrons and residual target electrons with attosecond temporal resolution. We calculated ab initio single-ionization spectra for photoemission from helium atoms by co-linearly polarized ultrashort XUV and assisting few-femtosecond IR pulses. Distinguishing direct and shake-up ionization resulting in ground-state and excited (n=2,3) He+ residual ions, respectively, we examined the effects of the correlated photoemission dynamics on the photoelectron phase-accumulation as a function of the observable photoelectron detection direction and kinetic energy, and XUV-IR pulse delay. We tracked the dynamical evolution of the residual ion in relative streaked photoemission delays and found dominant contributions for shake-up emission from the residual ion - photoelectron interaction. These are in very good and fair agreement, respectively, for n=2 and n=3 shake-up photoemission along the pulse-polarization directions, with previous experimental and theoretical investigations [Ossiander et. al. 2017] and reveal a strong photoemission-direction dependence for shake-up ionization due to the coupling between the photoelectron and evolving residual-ion charge distribution in the IR-laser field.