N. I. Shvetsov-Shilovski

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.

Dynamics of valence-shell electrons and nuclei probed by strong-field holography and rescattering

Strong-field photoelectron holography and laser-induced electron diffraction (LIED) are two powerful emerging methods for probing the ultrafast dynamics of molecules. However, both of them have remained restricted to static systems and to nuclear dynamics induced by strong-field ionization. Here we extend these promising methods to image purely electronic valence-shell dynamics in molecules using photoelectron holography. In the same experiment, we use LIED and photoelectron holography simultaneously, to observe coupled electronic-rotational dynamics taking place on similar timescales. These results offer perspectives for imaging ultrafast dynamics of molecules on femtosecond to attosecond timescales.

Optimal control of high-harmonic generation by intense few-cycle pulses

This work was supported by the Academy of Finland; COST Action CM1204 (XLIC); the European Community’s FP7 through the CRONOS project, Grant No. 280879; the European Research Council Advanced Grant DYNamo (Grant No. ERC-2010-AdG-267374); Grupos Consolidados UPV/EHU del Gobierno Vasco (Grant No. IT578-13); Spanish Grant No. FIS2010-21282-C02-01; and the University of Zaragoza (Project No. UZ2012-CIE-06).

Carrier?envelope phase effect in the yield of sequential ionization by an intense few-cycle laser pulse

The relative yield of highly charged atomic ions produced by a short (4?6?fs at FWHM) intense (1014?5???1018?W?cm?2) laser pulse was investigated by numerical solution of the rate equations. We predict oscillations of the ion yield as a function of the absolute phase. A distinctive property of this phase dependence is that it can only be observed when at least two ions have comparable yields. It is shown that with currently available laser systems the effect should be experimentally detectable for various rare gas atoms: Xe, Kr, Ar and Ne.

Two-dimensional streaking: complete characterization of an arbitrarily polarized few-cycle laser pulse using a stereodetector technique

We discuss the feasibility of measuring the temporal variation of the electric-field strength of a few-cycle laser pulse with arbitrary polarization using the attosecond streaking method. It is shown that a full characterization of the field requires measuring the photoelectron momenta in two opposite directions in the laser polarization plane for various delays of the extreme ultraviolet burst with respect to the probed laser pulse.

Two-step semiclassical model for strong-field ionization with interference and multielectron polarization effects

We present a semiclassical model for above-threshold ionization with the inclusion of the Stark shift of the initial bound state, the Coulomb potential, and a polarization induced dipole potential capable to describe quantum interference. The model will be used to investigate the imprints of polarization effects in the interference structure of electron momentum distributions.

Stable and efficient momentum-space solutions of the time-dependent Schrödinger equation for one-dimensional atoms in strong laser fields

One-dimensional model systems have a particular role in strong-field physics when gaining physical insight by computing data over a large range of parameters, or when performing numerous time propagations within, e.g., optimal control theory. Here we derive a scheme that removes a singularity in the one-dimensional Schrodinger equation in momentum space for a particle in the commonly used soft-core Coulomb potential. By using this scheme we develop two numerical approaches to the time-dependent Schrodinger equation in momentum space. The first approach employs the expansion of the momentum-space wave function over the eigenstates of the field-free Hamiltonian, and it is shown to be more efficient for laser parameters usual in strong field physics. The second approach employs the Crank-Nicolson scheme or the method of lines for time-propagation. The both methods are readily applicable for large-scale numerical simulations in one-dimensional model systems.