Alexander Galstyan

Modelling laser-atom interactions in the strong field regime

Abstract We consider the ionisation of atomic hydrogen by a strong infrared field. We extend and study in more depth an existing semi-analytical model. Starting from the time-dependent Schrödinger equation in momentum space and in the velocity gauge we substitute the kernel of the non-local Coulomb potential by a sum of N separable potentials, each of them supporting one hydrogen bound state. This leads to a set of N coupled one-dimensional linear Volterra integral equations to solve. We analyze the gauge problem for the model, the different ways of generating the separable potentials and establish a clear link with the strong field approximation which turns out to be a limiting case of the present model. We calculate electron energy spectra as well as the time evolution of electron wave packets in momentum space. We compare and discuss the results obtained with the model and with the strong field approximation and examine in this context the role of excited states. Graphical abstract

Effects of photon momentum in nonrelativistic (γ,2e) processes

We study the effects of nonzero photon momentum on the triply-differential cross section for (\gamma,2e) processes. Due to the low value of the photon momentum, these effects are weak and manifest only in special kinematical conditions like the back-to-back emission of the electrons with equal energy sharing. Helium and a few light helium-like ions are treated in detail. Quite unexpectedly, the magnitude of these effects is maximal for relatively small photon energies. However, although this effect on the TDCS remains rather small, of the order of a few mbarn eV^{-1} sr^{-2}, it is sufficient to be observed experimentally.

Fully differential cross sections for singly ionizing 1-MeV p+He collisions at small momentum transfer: Beyond the first Born approximation

We present calculations of the electron angular distributions in the single ionization of helium by 1-MeV proton impact at momentum transfer of 0.75 a.u. and ejected-electron energy of 6.5 eV. The results using the first and second Born approximations and the 3C model with different trial helium functions are compared to the experimental data. A good agreement between theory and experiment is found in the case of the 3C final state and a strongly correlated helium wave function. The electron-electron correlations in the He atom are found to influence the ratio of the binary and recoil peak intensities.

Strong field approximation within a Faddeev-like formalism for laser-matter interactions

Abstract We consider the interaction of atomic hydrogen with an intense laser field within the strong-field approximation. By using a Faddeev-like formalism, we introduce a new perturbative series in the binding potential of the atom. As a first test of this new approach, we calculate the electron energy spectrum in the very simple case of a photon energy higher than the ionisation potential. We show that by contrast to the standard perturbative series in the binding potential obtained within the strong field approximation, the first terms of the new series converge rapidly towards the results we get by solving the corresponding time-dependent Schrödinger equation. Graphical abstract

Ionisation of H 2 O by a strong ultrashort XUV pulse: a model within the single active electron approximation

Abstract We present and discuss a new computationally inexpensive method to study, within the single active electron approximation, the interaction of a complex system with an intense ultrashort laser pulse. As a first application, we consider the one photon single ionisation of the highest occupied molecular orbital of the water molecule by a laser pulse. The ionisation yield is calculated for different orientations of the molecule with respect to the field polarization axis and compared against predictions of another single active electron approach.

Perturbative expansions for laser-atom interactions

Synopsis We analyze the interaction of a one-active electron system with a strong laser field. In order to extract information about the interaction mechanisms, it is important to consider perturbative expansions of the ionization probability amplitude in terms of the Coulomb potential. Based on some of Faddeev ideas, we introduce a new perturbative series that involves both the Coulomb and the Volkov propagators. We show that for photon energies higher than the ionization potential, the series converges rapidly towards the exact result as calculated by solving numerically the time-dependent Schrödinger equation. In the same conditions, the well known strong field approximation series is shown to diverge.

Comment on "Dynamics of transfer ionization in fast ion-atom collisions"

We inspect the first-order electron-electron capture scenario for transfer ionization that has been recently formulated by Voitkiv et al. (Phys. Rev. A 86, 012709 (2012) and references therein). Using the multichannel scattering theory for many-body systems with Coulomb interactions, we show that this scenario is just a part of the well-studied Oppenheimer-Brinkmann-Kramers approximation. Accurate numerical calculations in this approximation for the proton-helium transfer ionization reaction exhibit no appreciable manifestation of the claimed mechanism.