Figure 1

The ion pair KER after strong-field double ionization of argon dimers at a laser pulse peak electric-field strength of 0.1 a.u. Solid (black) line, linear polarization; dashed (red) line, circular polarization of the laser beam.Reuse & Permissions

Figure 2

Angular distribution of the ion pair from DI of ${\mathrm{Ar}}_2$ for the KER line (a) in Fig. 1 (the direct Coulomb explosion line) for linearly polarized laser radiation. Plotted is the number of events per solid angle element $d\Omega =2\pi \cos \theta d\theta$ as a function of $\theta$, the angle between the laser beam polarization axis and the direction of emission of one of the ${\mathrm{Ar}}^{+}$ ions. For direct Coulomb explosion this angle is equal to the angle between the light polarization axis and the internuclear axis of the dimer at the instant of ionization. The laser pulse parameters are those of Fig. 1.Reuse & Permissions

Figure 3

The ion pair sum-momentum distributions for the KER lines (a) [dashed (red) lines] and (b) [solid (black) lines] in Fig. 1. The dotted (blue) lines are the momentum distributions for ${\mathrm{Ar}}^{2+}$ ions from DI of Ar atoms. Part (a) shows the momentum distributions for linear polarization and part (b) shows the momentum distributions for circular polarization of the laser beam. In (a) the momentum component along the direction of linear polarization is displayed and in (b) one of the two equivalent components in the plane of polarization is displayed.Reuse & Permissions

Figure 4

Schematic potential energy curves of ${{\mathrm{Ar}}_2}^{2+}$ and ${{\mathrm{Ar}}_2}^{+}$ relevant for the discussion of the experimental results. The vertical arrows indicate laser-induced DI of ${\mathrm{Ar}}_2$ and charge transfer in ${{\mathrm{Ar}}_2}^{2+}$ at the equilibrium internuclear separation $R_{\mathrm{eq}}$ of the ${\mathrm{Ar}}_2$ dimer. The arrow labeled “RCT” indicates reverse radiative charge transfer happening at small internuclear separation.Reuse & Permissions

Figure 5

(a) Scheme of the two possible interatomic Coulombic decay pathways of excited ${{\mathrm{Ar}}_2}^{+*}$ dimer ions. Left-hand side, ICD via virtual photon exchange; right-hand side, ICD via charge transfer at small internuclear separation. (b) Illustration of frustrated triple ionization of ${\mathrm{Ar}}_2$. For details see the text.Reuse & Permissions

Figure 6

Potential energy curves ($-1/|z+R_{\mathrm{eq}}/2|-2/|z-R_{\mathrm{eq}}/2|$) for electron motion along the internuclear axis in a model ${{\mathrm{Ar}}_2}^{2+}$ dimer ion plotted for an internuclear separation $R=R_{\mathrm{eq}}$ [solid (red) line]. The dashed (red) line indicates the same potential as before, however, now superimposed with the potential of a homogeneous external electric field. The external field strength is chosen to be equal to the peak laser pulse field strength of $0.1$ a.u. in the experiment. The two horizontal lines represent the two lowest lying electronic energy eigenvalues of ${{\mathrm{Ar}}_2}^{2+}$ (from [15]). Superimposed on these lines, we show the corresponding electronic wave functions we derived for a one-dimensional model ${{\mathrm{Ar}}_2}^{2+}$ dimer. In the ground state the electron is localized at the ${{\mathrm{Ar}}_2}^{2+}$ site. As can be seen the first excited state is the charge transfer state where the electron is mainly localized at the ${\mathrm{Ar}}^{+}$ site. The zero point of the energy scale corresponds to removal of the electron to infinity with the two nuclei fixed at $R_{\mathrm{eq}}$.Reuse & Permissions

Figure 7

Evolution in time of the electronic wave function of the initially two-site ionized model ${\mathrm{Ar}}_2$ dimer with an external 10-cycle laser pulse applied which has a peak electric-field strength of $0.075$ a.u. On a logarithmic color scale we show a density plot of the wave packet probability distribution $|\psi (z,t)|{}^2$. Time evolves along the vertical axis. It is given in multiples of the laser light period $T=2.67$ fs. The inserted curves shows the absolute square of the two-site (right-hand maximum) and of the one-site (left-hand main maximum) ionized electronic eigenstates of the model atom. For further details see the text.Reuse & Permissions

Figure 8

KER distribution for the Coulomb explosion channel ${\mathrm{Ar}}^{2+}+{\mathrm{Ar}}^{+}$ after triple ionization of the ${\mathrm{Ar}}_2$ dimer [dashed (blue) line]. The spectrum was taken simultaneously with the corresponding KER spectrum for the Coulomb explosion channel ${\mathrm{Ar}}^{+}+{\mathrm{Ar}}^{+}$ in Fig. 1 with the laser beam having linear polarization. On the vertical axis the number of ion pair events per energy bin is given. Also shown is the vertically scaled high-energy part of the KER spectrum in Fig. 1 taken with linear polarization [solid (black) line]. The dotted (red) line line is a fit to the measured KER line (c) of Fig. 1 assuming that it originates from frustrated triple ionization of ${\mathrm{Ar}}_2$. For details see the text.Reuse & Permissions