Corrélations électroniques dans l'ionisation-excitation de l'hélium par photons XUV ou électrons rapides et anomalie du moment magnétique de l'électron dans la diffusion de Mott en champ laser intense

In this work, we investigate the role of the electronic correlations in the two-photon XUV single ionization-excitation and in the electron-impact ionization-excitation of the helium atom. In the two-photon process, we show by means of perturbative Floquet treatment that like for the sequential transition, the core resonances are present in the partial and total cross sections in a regime where two-photon double ionization is direct. We analyse the physical origin of these resonances. Concerning the electron-impact process, we use a first-order time-independent perturbative theory where the wave function of the initial and the final states includes the electronic correlation rigourously. In particular, we study the role of the exit channels leading to the autoionization of the atom. A detailed comparison between theoretical predictions and experimental data is presented and discussed. Interesting perspectives are given in the conclusion. We investigate the influence of the electron's anomalous magnetic moment on the process of relativistic Mott scattering in a powerful electromagnetic plane wave for which the ponderomotive energy is of the order of the magnitude of the electron's rest mass. For this purpose, we use the Coulomb-Dirac-Volkov and the Dirac-Volkov functions with the electron's anomaly to describe the initial and final states respectively. First-order Born differential cross sections of induced and inverse bremsstrahlung are obtained for linearly and circularly polarized laser light. Numerical calculations are carried out for various parameters values, (i.e. scattering angle, the nucleus charge, photon energy, electrical field) and are compared with results obtained by Li et al. [J. Phys. B: At. Mol. Opt. Phys. 37, 653 (2004)]. It is found that for parameters used in the present work, incorporating the anomaly of the electron in the initial and final states yields cross sections which are strongly modified whatever the scattering geometry as compared to the outcome of the previous treatment.