Sequential two-photon double ionization of Kr atoms

Abstract

Sequential two-photon double ionization of Kr atoms is theoretically considered. The angular distribution of emitted electrons is calculated with the dipole amplitudes evaluated within the multiconfigurational Hartree-Fock and Dirac-Fock approaches. The difference in angular distributions for two-photon and single-photon ionization is discussed.

Two-Photon Excitation and Relaxation of the3d−4dResonance in Atomic Kr

“…This new phenomenon, which will be present in all processes involving the interaction between intense XUV light and matter, can be addressed only due to the short pulse durations. It is the nonlinear behavior of such interactions that presents a new frontier, with multiphoton excitation and/or ionization of subvalence electrons representing the backbone of the underlying physics.Given the novelty of the sources and the hitherto largely unexplored radiation-matter territory at XUV and x-ray photon energies, certain benchmark experimental studies are necessary in order to provide a first assessment of their feasibility as well as the predictive potential of relevant theoretical and computational approaches (e.g., [8,9]). It is important to recall that the so-called single active electron approximation, often adopted in the long-wavelength regime, is not valid in the short-wavelength regime.…”

“…Given the novelty of the sources and the hitherto largely unexplored radiation-matter territory at XUV and x-ray photon energies, certain benchmark experimental studies are necessary in order to provide a first assessment of their feasibility as well as the predictive potential of relevant theoretical and computational approaches (e.g., [8,9]). It is important to recall that the so-called single active electron approximation, often adopted in the long-wavelength regime, is not valid in the short-wavelength regime.…”

“…In general, the intensity ratios of most peaks, especially between the 4p line and the resonant Auger lines, is well reproduced. However, the kinetic energies of the Auger lines to the Kr þ 4p 4 4d 2;4 L J final states are higher than the experimental values by about 2 eV, which most likely arises from the strong coupling of the 3d 9 5=2 4d resonances to the continuum [19] and a slightly unbalanced treatment of correlation effects in the neutral and singly ionized Kr. The calculated overall intensity for the two-photon processes corresponds well to the experimental values.…”

Electron angular distributions of noble gases in sequential two-photon double ionization

“…In our experiments, the FEL wavelength bandwidth did not allow to resolve the spin-orbit multiplets of either the singly charged intermediate state 2 Our results for the second step ionization electron angular distributions of neon, argon and krypton compiled in table 1 are discussed in the following and compared to two recent theoretical studies which differ mainly in assumptions concerning coherency of excitation of the intermediate ion fine structure levels 2 P 1/2,3/2 . In the density matrix and statistical tensor formalism used by Fritzsche et al [28,30,36] the excitation is considered completely incoherent (LSJ-coupling scheme), whereas Kheifets [29] used a model with completely coherent excitation of these levels (LS-coupling scheme). The latter work employs the graphical angular momentum coupling technique to derive analytical formulas for the β parameters which contain the radial dipole matrix elements.…”

“…Hence, anisotropic final state interactions are expected to occur [27]. Some recent calculations predict indeed large effects with respect to the higher order anisotropy parameter β 4 , showing completely different behaviour in the region of the Cooper-minima for the different multiplets [28][29][30]. The intense free-electron laser radiation is capable of creating a dense ionic target which can be further ionized within the same light pulse.…”