Figure 1

Scheme of the PCI effect. A photoelectron (PE, created at time $t_p$) is overtaken by a faster Auger electron (AE, created at time $t_p+{\tau }_A$) at time $t^{*}$ and distance $r^{*}$ from the ion. The binding potential $V_{\mathrm{ei}}(r)$ changes from $-1/r$ to $-2/r$, for the PE, and vice versa for the AE, resulting in an energy gain (loss) $\Delta E_{\mathrm{PCI}}$ of the AE (PE).Reuse & Permissions

Figure 2

Light-field-assisted PCI for two successive zeroes of the streaking vector potential, corresponding to positive (left graph) and negative (right graph) time derivative. An AE created at time ${\tau }_A$ after the PE arrives at the detector with an energy gain $ϵ({\tau }_A,t_p)$, bold red curve. The exponential ionization probability $T_A({\tau }_A)$ is mapped onto the AE energy distribution $f_{\mathrm{PCI}}^{\pm }(ϵ)$, red curve via Eq. (6), as indicated by the arrows for two Auger release times (0.3 and 9 fs). In the absence of PCI, the energy distributions in the two cases have the same shape [gray curves labeled $f$, Eq. (3)], deriving from the linear time-energy relation (dashed gray lines). PCI without streaking field causes a broadening of the line and shift to higher energies (blue curves $f_{\mathrm{PCI}}^0$). Values refer to Xe NOO Auger decay and streaking with 1 THz at experimental conditions.Reuse & Permissions

Figure 3

Series of kinetic energy spectra of Xe $4d$ photoelectrons and Auger electrons formed after absorption of XUV photons in the presence of a terahertz field with a variable time delay. Data are recorded with the accelerator-based terahertz-field-driven streak camera at field strengths of $120\mathrm{kV}/\mathrm{cm}$. Note that the ascending (descending) slope of the kinetic energy shift corresponds to the descending (ascending) slope of the streaking vector potential. Marked in white are the FWHM widths of Gaussian functions fitted to the Auger lines of the spectra indicated by the white arrows. The corresponding width uncertainties are 0.03 eV.Reuse & Permissions

Figure 4

Comparison of calculated and measured Xe NOO (left) and Kr MNN (right) Auger spectra with and without (a, d) terahertz field. FAPCI causes a linewidth asymmetry for the spectra measured close to a zero crossing at the descending (b, e) and ascending (c, f) slope of the vector potential. In the Auger line labels, the medium terms $O_{2,3}{O}_{2,3}$ for Xe and $N_1{N}_{2,3}$ for Kr are omitted for a better readability. The FWHM widths $w$ of Gaussian functions fitted to the Auger lines are given.Reuse & Permissions