H2+ ionization by ultra-short electromagnetic pulses investigated through a non-perturbative Coulomb-Volkov approach

V. D. RODRÍGUEZ; P.A. MACRI; R. GAYET

Rosario, Argentina

Conferencia; 24th International Conference on the Physics of Electronic, Photonic and Atomic Collision (XXIV ICPEAC) Rosario, Argentina (2005); 2005

H2+ ionization by ultra-Short electromagnetic pulses investigatedthrough a non-perturbative Coulomb-Volkov approach V. D. Rodríguez1, P. A. Macri1,2 and R. Gayet3 1) Departamento de Física, FCEyN, Universidad de Buenos Aires, 1428 Buenos Aires, Argentina. 2) Instituto de Astronomía y Física del Espacio, 1428 Buenos Aires, Argentina. 3) CELIA, Université Bordeaux 1, 351 Cours de la Libération, 33405 Talence Cedex, France.       Interference phenomena should occur when electrons are released from molecules interacting with a short laser pulse. Just like in a Young experiment, we can regard the atoms as photon absorbers, which play the role of separate and coherent sources of photoelectrons, thus leading to electron interference patterns. For diatomic molecules, these interference patterns should show a periodicity depending on the ratio of the internuclear distance to the photoelectron wavelength. This interference may modulate the ionization cross sections. Although interference phenomena have been identified for many years in the case of photoionization, interference effects have been observed only very recently in electron spectra produced by high-energy collisions of heavy ions with H2 molecules [1].       In the present work, CV1 approach [2] is adapted to explore its ability to investigate the rich range of effects appearing in the ionization of the H2+ molecular ion by ultra-short laser pulses. The initial active-electron wave function is approximated here by a Linear Combination of Atomic Orbitals (LCAO) with two variational single-zeta functions. We will assume that the ejected electron is described by a two-center continuum satisfies exact limit of the outgoing wave in the field of the two nuclei [3]. In figure 1, we set the electric field amplitude in the non- perturbative regime F0 = 1 au and evaluate the fivefold ionization probabilities (FDIP) as a function of the electron ejection angle q  for fixed two electron energies and a molecular orientation perpendicular to the field polarization. In both cases, we observe that all the FDIP’s present a prominent lobe in the backward direction ought to the action of the strong field. However, although with lower intensity, the electron distribution displays other maxima at different angles. From the figure, it is clear how new lobes emerge in the FDPI as the electron energy increases.      The structure is modeled by the interference factor  times an atomic ionization probability, which is strongly peaked in the backward direction. Being , and  the momentum transferred by the field to the electron, the electron momentum and  the internuclear distance vector, respectively. Figure 1. FDIPs for an electron ionized from a molecule with axes perpendicular to the electric field for different electron ionization energies. References [1] Stolterfoht N et al 2001, Phys. Rev. Lett. 87,      023201 [2] Duchateau G, Cormier E, Bachau H and Gayet R 2001, Phys. Rev. A 63, 053411 [3] Joulakian B, Hanssen J, Rivarola R and      Motassim A 1996, Phys. Rev. A 54, 1473