R Della Picca

Vortices in ionization collisions by positron impact

The presence of vortices in the ionization of hydrogen atoms by positrons at intermediate impact energies is investigated. The present findings show that a previously reported minimum in the fully differential cross section is the signature of a vortex in the continuum positron–electron–proton system. The behaviour of the real and imaginary parts of the complex-valued transition matrix is studied in order to determine and characterize the vortex in momentum space. The obtained information is translated to fully differential ionization cross sections, feasible of being measured with currently available techniques.

Angular distributions of photoelectrons emitted from fixed in-space hydrogen molecular ions

We study the angular distribution of photoelectrons emitted from H+2. For this purpose we employ exact electronic continuum wavefunctions obtained numerically by solving the time-independent Schrodinger equation. We calculate the differential cross sections at fixed photoelectron energy and compare our results with previous calculations which employ perturbative solutions for the continuum wavefunctions. Important discrepancies in the angular distributions below 100 eV are found and discussed. We also analyse the influence that has the representation of the initial bound state wavefunction and calculate the total cross sections to compare with exact values.

Laser pulse ionization of fixed-in-space H2O

We present a detailed study of the ionization probability of H2O induced by a short intense laser pulse. Within the strong-field approximation, we present total and differential ionization probabilities of the water molecule fixed in space. It is shown that the second highest occupied molecular orbital (HOMO-1) dominates the single-electron emission process when the laser is polarized along the symmetry axis of the H2O molecule, and that the electron emission is in general favoured in the direction along the laser polarization direction.

Factorization of laser-pulse ionization probabilities in the multiphotonic regime

We present a detailed study of the ionization probability of H and H induced by a short intense laser pulse. Starting from a Coulomb–Volkov description of the process we derive a multipole-like expansion where each term is factored into two contributions: one that accounts for the effect of the electromagnetic field on the free-electron final state and a second factor that depends only on the target structure. Such a separation may be valuable to solve complex atomic or molecular systems as well as to interpret the dynamics of the process in simpler terms. We show that the series expansion converges rapidly, and thus the inclusion of the first few terms is sufficient to produce accurate results.

Beryllium ionisation by ion impact

We study ionization of Beryllium atoms by ion impact with continuum distorted waves models. We calculate cross sections in the intermediate to high energy regime for state resolved and total ionization.

Above threshold ionization of Argon atoms by multicolor XUV radiation

We analyse theoretically the Argon photoelectron spectra produced by strong and extreme ultraviolet radiation of six colors: from the 11th to the 16th harmonics of ω0 (800nm). In particular we concentrate in the range of the spectra where absorption of two photons occurs. The combination of photons of different frequencies results in eleven peaks that are separated by ω0. We point out that their relative intensities are very sensitive to the laser pulse parameters and target description. We also compare the theoretical description with experimental results finding good qualitative agreement.

W63+ and W64+ ionization by protons and photons

In this work we investigate the ionization by proton impact, and photo ionization, involving highly charged ions of W, in particular the Ne-like W64+ and Na-like W63+ which are more likely to appear in ITER plasma. Total cross sections are calculated in the continuum-distorted-wave-eikonal-initial-state (CDW-EIS) approximation for ion-impact, while two completely different methods are used for photoionization: a perturbative dipolar aproach and the recently introduced Sturmian model.

Multicolor XUV above threshold ionization of argon

Argon photo-electron spectra produced by short-pulse extreme ultraviolet radiation, and with particular emphasis on the two-photon absorption region, is analyzed theoretically. The electromagnetic pulse is modeled to resemble experimentally available pulses and is built from a range of high-harmonics from an 800 nm laser. The photo-electron spectra show a characteristic peak structure due to the absorption of different combinations of photons, where the relative peak intensity is very sensitive to both the XUV pulse parameters and the target description. The theoretical result is further compared with experimental data, and good qualitative agreement is found.