M. F. Ciappina

Multislit interference patterns in high-order harmonic generation in C60

We study high-order harmonic generation in C{sub 60} molecules interacting with a linearly polarized intense short laser pulse at near- and mid-infrared wavelengths, using an extension of the so-called three-step or Lewenstein model to the molecular case. The results exhibit modulations in the plateaus of the spectra at the longer wavelengths, which are present for ensembles of aligned as well as randomly oriented fullerenes. The analysis of the results show that the minima can be explained by a multislit interference effect arising from the contributions of the 60 atomic centers to the dipole moment. Good agreement between the positions of the minima in the spectra obtained in the length gauge are found with those of the recombination matrix element, but not for those in the velocity gauge calculations. We further use a simple spherical model to analyze how geometrical information, such as the radius of the fullerene cage, can be obtained from the interference pattern in the harmonic spectra.

Fully differential study of ionization in p + H2 collisions near electron-projectile velocity matching

We have performed a kinematically complete experiment on ionization of H2 by 75 keV proton impact for electrons ejected with a speed close to the projectile speed. The fully differential data are compared to a three-body distorted wave and a continuum distorted wave—eikonal initial state calculation. Large discrepancies between experiment and theory, as well as between both calculations, are found. These probably arise from a strong coupling between the ionization and capture channels, which is not accounted for by theory.

Monte Carlo event generators in atomic collisions: A new tool to tackle the few-body dynamics

The Monte Carlo Event Generator technique is applied to study the reaction dynamics of atomic processes induced by ion and electron impact as well as by strong laser fields.

Fully Differential Study of Capture with Vibrational Dissociation in p+H2 Collisions

We have measured fully differential cross sections for electron capture in 75xa0keV p+H_{2} collisions with subsequent dissociation of the intermediate molecular H_{2}^{+} ion by vibrational excitation using different projectile coherence lengths. Data were obtained for two molecular orientations as a function of projectile scattering angle. Two types of interference, single- and molecular two-center interference, were identified. The two-center interference structure is phase shifted by π compared to what we expected. Furthermore, the presence of projectile coherence effects could be reconfirmed.

Fully differential cross sections for ionization of H2 molecules by proton impact: single- and two-centre effects

Fully differential cross sections for ionization of H2 by 75 keV proton impact are compared with recent experimental data. Calculations were obtained by using a two-effective centre approximation within the CDW-EIS approach.

Distorted Wave Theories Applied to Double Ionization by Ion Impact: Simulation of Higher-Order Processes

One of the goals in studies of double ionization (DI) of simple atoms by electronnor ion impact is to elucidate and assess the different mechanisms that lead to thisnatomic process. In this work we present an attempt to model the mechanisms beyondnthe first order in DI of helium by highly charged projectiles. To this end wenemploy the continuum distorted wave-eikonal initial state (CDW-EIS) formalismnjoint with a Monte Carlo event generator (MCEG). The MCEG allows us to generatentheoretical event files that represent the counterpart of the data obtained fromna kinematically complete experiment. Starting from these event files, a new datananalysis tool used to contrast theory and experiment in DI, the four-body Dalitznplots, is easily produced. The higher order mechanisms are simulated by consideringnDI as a sequential process: a single ionization of a helium atom as a first step andnanother single ionization of a single-charged helium ion as a second step. Some ofnthe features in the experimental data are very well reproduced by these simulations.