12 research outputs found
Capture into Rydberg states and momentum distributions of ionized electrons
The yield of neutral excited atoms and low-energy photoelectrons generated by
the electron dynamics in the combined Coulomb and laser field after tunneling
is investigated. We present results of Monte-Carlo simulations built on the
two-step semiclassical model, as well as analytic estimates and scaling
relations for the population trapping into the Rydberg states. It is shown that
mainly those electrons are captured into bound states of the neutral atom that
due to their initial conditions (i) have moderate drift momentum imparted by
the laser field and (ii) avoid strong interaction ("hard" collision) with the
ion. In addition, it is demonstrated that the channel of capture, when
accounted for in semiclassical calculations, has a pronounced effect on the
momentum distribution of electrons with small positive energy. For the
parameters that we investigated its presence leads to a dip at zero momentum in
the longitudinal momentum distribution of the ionized electrons.Comment: 9 pages, 8 figures in one zip-archiv
Laser assisted decay of quasistationary states
The effects of intense electromagnetic fields on the decay of quasistationary
states are investigated theoretically. We focus on the parameter regime of
strong laser fields and nonlinear effects where an essentially nonperturbative
description is required. Our approach is based on the imaginary time method
previously introduced in the theory of strong-field ionization. Spectra and
total decay rates are presented for a test case and the results are compared
with exact numerical calculations. The potential of this method is confirmed by
good quantitative agreement with the numerical results.Comment: 24 pages, 5 figure
Recommended from our members
The plateau in above-threshold ionization: the keystone of rescattering physics
A review is presented of the rescattering plateau in laser-induced above-threshold ionization and its various features as they were discovered over time. Several theoretical explanations are discussed, from simple momentum conservation to the quantum-mechanical improved strong-field approximation and the inherent quantum orbits or, alternatively, entirely classical methods. Applications of the plateau to the extraction of atomic or molecular potentials and to the characterization of the driving laser pulse are also surveyed
Interference Carpets in Above-Threshold Ionization: From the Coulomb-Free to the Coulomb-Dominated Regime
Displaced creation
The ionization of atoms and molecules by strong laser fields has become a core technique in modern laser physics. Now, the electrons emerging from ionized molecules are shown to exhibit a memory of the ionization process, resulting in a spatial phase that may influence the interpretation of imaging data
Ionization in elliptically polarized pulses: Multielectron polarization effects and asymmetry of photoelectron momentum distributions
Electron-electron dynamics in laser-induced nonsequential double ionization.
For the description of nonsequential double ionization (NSDI) of rare-gas atoms by a strong linearly polarized laser field, the quantum-mechanical S-matrix diagram that incorporates rescattering impact ionization is evaluated in the strong-field approximation. We employ a uniform approximation, which is a generalization of the standard saddle-point approximation. We systematically analyze the manifestations of the electron-electron interaction in the momentum distributions of the ejected electrons: for the interaction, by which the returning electron frees the bound electron, we adopt either a (three-body) contact interaction or a Coulomb interaction, and we do or do not incorporate the mutual Coulomb repulsion of the two electrons in their final state. In particular, we investigate the correlation of the momentum components parallel to the laser-field polarization, with the transverse momentum components either restricted to certain finite ranges or entirely summed over. In the latter case, agreement with experimental data is best for the contact interaction and without final-state repulsion. In the former, if the transverse momenta are restricted to small values, comparison of theory with the data shows evidence of Coulomb effects. We propose that experimental data selecting events with small transverse momenta of both electrons are particularly promising in the elucidation of the dynamics of NSDI. Also, a classical approximation of the quantum-mechanical S matrix is formulated and shown to work very well inside the classically allowed region