Attosecond time-scale multi-electron collisions in the Coulomb four-body problem: traces in classical probability densities

In the triple ionization of the Li ground state by single photon absorption the three electrons escape to the continuum mainly through two collision sequences with individual collisions separated by time intervals on the attosecond scale. We investigate the traces of these two collision sequences in the classical probability densities. We show that each collision sequence has characteristic phase space properties which distinguish it from the other. Classical probability densities are the closest analog to quantum mechanical densities allowing our results to be directly compared to quantum mechanical results.Comment: 9 pages, 10 figure

Controlling electron-electron correlation in frustrated double ionization of molecules with orthogonally polarized two-color laser fields

We demonstrate the control of electron-electron correlation in frustrated double ionization (FDI) of the two-electron triatomic molecule D$_{3}^{+}$ when driven by two orthogonally polarized two-color laser fields. We employ a three-dimensional semi-classical model that fully accounts for the electron and nuclear motion in strong fields. We analyze the FDI probability and the distribution of the momentum of the escaping electron along the polarization direction of the longer wavelength and more intense laser field. These observables when considered in conjunction bear clear signatures of the prevalence or absence of electron-electron correlation in FDI, depending on the time-delay between the two laser pulses. We find that D$_{3}^{+}$ is a better candidate compared to H$_{2}$ for demonstrating also experimentally that electron-electron correlation indeed underlies FDI.Comment: 5 pages, 4 figure

Frustrated double ionization in two-electron triatomic molecules

Using a semi-classical model, we investigate frustrated double ionization (FDI) in $\mathrm{D_3^+}$, a two-electron triatomic molecule, when driven by an intense, linearly polarized, near-infrared (800 nm) laser field. We compute the kinetic energy release of the nuclei and find a good agreement between experiment and our model. We explore the two pathways of FDI and show that, with increasing field strength, over-the-barrier ionization overtakes tunnel ionization as the underlying mechanism of FDI. Moreover, we compute the angular distribution of the ion fragments for FDI and identify a feature that can potentially be observed experimentally and is a signature of only one of the two pathways of FDI.Comment: 5 pages, 4 figure

Intertwined electron-nuclear motion in frustrated double ionization in driven heteronuclear molecules

We study frustrated double ionization in a strongly-driven heteronuclear molecule HeH$^{+}$ and compare with H$_2$. We compute the probability distribution of the sum of the final kinetic energies of the nuclei for strongly-driven HeH$^{+}$. We find that this distribution has more than one peak for strongly-driven HeH$^{+}$, a feature we do not find to be present for strongly-driven H$_{2}$. Moreover, we compute the probability distribution of the n quantum number of frustrated double ionization. We find that this distribution has several peaks for strongly-driven HeH$^{+}$, while the respective distribution has one main peak and a "shoulder" at lower n quantum numbers for strongly-driven H$_{2}$. Surprisingly, we find this feature to be a clear signature of the intertwined electron-nuclear motion