Yuri V. Popov

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 Volkov functions in laser-assisted electron momentum spectroscopy

We consider theoretically an electron-impact ionization process at high impact energy and large momentum transfer in the presence of laser radiation. The target is modeled as an electron bound by a harmonic potential. Dressing of the target state by the laser field is treated exactly. Laser-assisted differential cross sections are calculated using either Volkov functions or plane waves for incoming and outgoing electrons. It is shown that even in the case of the low-frequency and weak-intensity laser radiation the effect of the field on these electrons can dramatically influence the shape of the cross sections.

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.

Model of interaction of zero-duration laser pulses with an atom

The soluble model of interaction of a finite series of zero - duration pulses with an atom is considered. The model is based on the nowadays laser techniques providing duration of pulses of a few femtoseconds and even less, and intensities higher than 1014-1020 Wt/cm2.

An Application of The Coulomb Scattering Theory to Ionization Processes

The goal of the article is to formulate consistent approximations for the Coulomb wave functions and the ionization scattering amplitudes, in particular, for the (e, 2e) reactions within the framework of the rigorous multichannel Coulomb scattering theory. A variant of the integral equation method is developed by applying the rearrangement technique to the original multichannel Lippmann-Schwinger equation for the transition operator T(Z). This technique is based on the singularity properties of the Coulomb Green’s function G(Z) when the argument Z tends to the energy shell. The rigorous mathematical proof is given that the approximation proposed includes entirely the Born-like terms up to the second order.

One-dimensional "atom" with zero-range potential perturbed by finite sequence of zero-duration laser pulses

The exactly soluble model of a train of zero-duration electromagnetic pulses interacting with a 1D atom with short-range interaction potential modelled by a δ-function is considered. The model is related to the up-to-date laser techniques providing the duration of pulses as short as a few attoseconds and the intensities higher than 1014 W/cm2.

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.

Theoretical study on laser-assisted electron momentum spectroscopy of helium

Ionization-excitation of helium by fast electron impact at large energy and momentum transfer and in the presence of a linearly polarized laser field is considered theoretically. The momentum profiles of He for transitions to the n = 1 and 2 states of He+ are discussed.

Semi-analytical model of hydrogen ionization by strong laser pulse at low field frequencies

We consider the interaction of hydrogen atom with a very intense low frequency laser pulse. The Henneberger-Kramers representation of the time-dependent Schrodinger equation is the most appropriate one for this purpose. It is shown that in the case of very low frequencies, the quantum dispersion of the electron wave packet plays a dominant role in the dynamics of the atom.

Comment on ‘Four-body charge transfer processes in proton–helium collisions’

We found, within the plane-wave first Born approximation, that the proton–helium fully differential cross section for transfer excitation agrees well with the experimental one at the proton energy Ep = 300 keV and small scattering angles both in shape and in magnitude. This result is in contradiction with that obtained in Chowdhury et al (2012 J. Phys B: At. Mol. Opt. Phys. 45 035203).