Semiclassical two-step model for ionization of hydrogen molecule by strong laser field

We extend the semiclassical two-step model for strong-field ionization that describes quantum interference and accounts for the Coulomb potential beyond the semiclassical perturbation theory to the hydrogen molecule. In the simplest case of the molecule oriented along the polarization direction of a linearly polarized laser field, we predict significant deviations of the two-dimensional photoelectron momentum distributions and the energy spectra from the case of atomic hydrogen. Specifically, for the hydrogen molecule the electron energy spectrum falls off slower with increasing energy, and the holographic interference fringes are more pronounced than for the hydrogen atom at the same parameters of the laser pulse.Comment: 9 pages, 6 figure

Ionization of atoms by few-cycle EUV laser pulses: carrier-envelope phase dependence of the intra-pulse interference effects

We have investigated the ionization of the H atom by intense few-cycle laser pulses, in particular the intra-pulse interference effects, and their dependence on the carrier-envelope phase (CEP) of the laser pulse. In the final momentum distribution of the continuum electrons the imprint of two types of intra-pulse interference effects can be observed, namely the temporal and spatial interference. During the spatial interference electronic wave packets emitted at the same time, but following different paths interfere leading to an interference pattern measurable in the electron spectra. This can be also interpreted as the interference between a direct and a scattered wave, and the spatial interference pattern as the holographic mapping (HM) of the target. This HM pattern is strongly influenced by the carrier-envelope phase through the shape of the laser pulse. Here, we have studied how the shape of the HM pattern is modified by the CEP, and we have found an optimal CEP for the observation of HM

Ionization of helium by slow antiproton impact: total and differential cross sections

We theoretically investigate the single and double ionization of the He atom by antiproton impact for projectile energies ranging from $3$~keV up to $1000$~keV. We obtain accurate total cross sections by directly solving the fully correlated two-electron time-dependent Schr\"odinger equation and by performing classical trajectory Monte-Carlo calculations. The obtained quantum-mechanical results are in excellent agreement with the available experimental data. Along with the total cross sections, we also present the first fully \textit{ab initio} doubly differential data for single ionization at 10 and 100~keV impact energies. In these differential cross sections we identify the binary-encounter peak along with the anticusp minimum. Furthermore, we also point out the importance of the post-collisional electron-projectile interaction at low antiproton energies which significantly suppresses electron emission in the forward direction

Guiding of KeV Ions between Two Insulating Parallel Plates

Experimental data are presented for low-energy singly charged ion transport between two insulating parallel plates. Using a beam intensity of approximately 20 pA, measurements of the incoming and transmitted beams provide quantitative temporal information about the charge deposited on the plates and the guiding probability. Using a smaller beam intensity (~ 1 pA) plate charging and discharging properties were studied as a function of time. These data imply that both the charge deposition and decay along the surface and through the bulk need to be modeled as acting independently. A further reduction of beam intensity to ~ 25 fA allowed temporal imaging studies of the positions and intensities of the guided beam plus two bypass beams to be performed. SIMION software was used to simulate trajectories of the guided and bypass beams, to provide information about the amount and location of deposited charge and, as a function of charge patch voltage, the probability of beam guiding and how much the bypass beams are deflected plus to provide information about the electric fields. An equivalent electric circuit model of the parallel plates, used to associate the deposited charge with the patch voltage implies that the deposited charge is distributed primarily on the inner surface of the plates, transverse to the beam direction, rather than being distributed throughout the entire plate

Semiclassical two-step model for strong-field ionization

We present a semiclassical two-step model for strong-field ionization that accounts for path interferences of tunnel-ionized electrons in the ionic potential beyond perturbation theory. Within the framework of a classical trajectory Monte-Carlo representation of the phase-space dynamics, the model employs the semiclassical approximation to the phase of the full quantum propagator in the exit channel. By comparison with the exact numerical solution of the time-dependent Schr\"odinger equation for strong-field ionization of hydrogen, we show that for suitable choices of the momentum distribution after the first tunneling step, the model yields good quantitative agreement with the full quantum simulation. The two-dimensional photoelectron momentum distributions, the energy spectra, and the angular distributions are found to be in good agreement with the corresponding quantum results. Specifically, the model quantitatively reproduces the fan-like interference patterns in the low-energy part of the two-dimensional momentum distributions as well as the modulations in the photoelectron angular distributions.Comment: 31 pages, 7 figure

Simulation of attosecond streaking of electrons emitted from a tungsten surface

First time-resolved photoemission experiments employing attosecond streaking of electrons emitted by an XUV pump pulse and probed by a few-cycle NIR pulse found a time delay of about 100 attoseconds between photoelectrons from the conduction band and those from the 4f core level of tungsten. We present a microscopic simulation of the emission time and energy spectra employing a classical transport theory. Emission spectra and streaking images are well reproduced. Different contributions to the delayed emission of core electrons are identified: larger emission depth, slowing down by inelastic scattering processes, and possibly, energy dependent deviations from the free-electron dispersion. We find delay times near the lower bound of the experimental data

Atomic data for integrated tokamak modelling – Fermi-shuttle type ionization as a possible source of high energy electrons

The ionization of Ar by 15 keV N+ ion is studied theoretically. The energy distributions of the ejected electrons as a function of the scattering angle were calculated using the classical trajectory Monte Carlo method. We identify the signature of the Fermi-shuttle type ionization in the double differential cross sections which should be a possible source of the high energy electrons in the plasma. Our classical calculation also describes the previously measured data with high accuracy

Ionization of the hydrogen atom by intense ultrashort laser pulses

The ionization of atomic hydrogen in intense laser fields is studied theoretically. The calculations were performed applying both quantummechanical and classical approaches. Treating the problem quantummechanically, the time dependent Schr\"odinger equation (TDSE) of our system was first transformed into a pseudo-momentum space and solved in this space iteratively. While neglecting the Coulomb potential during the solution of the TDSE we got the results in the Volkov approximation, in the first order solution we taken into account the Coulomb potential as perturbation. The classical calculations were performed within the framework of the classical trajectory Monte-Carlo (CTMC) method. The double differential ionization probabilities are calculated for different laser pulses and a reasonable agreement was found between the theories. Major differences can be observed in the angular distribution of electrons at low electron energies between classical and the quantummechanical approaches. At high electron energies the differences disappear, which indicates that the generation of low energy electrons is of quantum type, and it is strongly influenced by the Coulomb potential, while the production of high energy electrons is of classical type and it is less influenced by the Coulomb interaction. Our results are also compared with the Coulomb-Volkov (CV) model calculations.Comment: submited to PR