Resonant laser assisted excitation

in electron-helium collisions

 

A. Makhoute1,2,*, H. Agueny1,3, S. Chqondi1,3

1UFR de Physique du Rayonnement et des Interactions Laser-Matière,Faculté des Sciences.

Université Moulay Ismail,B.P. 11201, Zitoune, Meknès, Morocco

2The Abdus Salam International Centre for Theoretical Physics, Strada costiera, II - 34100 Trieste, Italy

3Laboratoire de Chimie Physique -Matière et Rayonnement, Université Pierre et Marie Curie,11 rue Pierre et Marie Curie,

 75231 Paris Cedex 05, France

* Corresponding author. E-mail: makhoute@fs-umi.ac.ma

Received: 16 May 2012; revised version accepted: 30 May 2012

 

Abstract

We study the electron-impact excitation of an atom, in the presence of a linearly polarized resonant laser field accompanied by the transfer of L photons. The incident electron is considered to be dressed by the laser field in a nonperturbative manner by choosing the Volkov solutions in both the initial and final channels. The laser-target interaction is treated nonperturbatively, while the electron-atom interaction is treated within the first Born approximation. Differential cross sections for excitation scattering with no net exchange and net exchange of one photons are calculated for a fixed incident electron energy. A detailed analysis is made of the excitation of the 11S->21S, 11S->21P, 11S->31S and 11S->31transitions, and for frequency of the laser field is chosen to match with 21S-21P or 31S-31P transition frequency in helium atom. Except for very small deturnings, the agreement between the perturbative and nonperturbative results corresponding to nearly equivalent final energies is excellent. The nonperturbative approach predicts no maximum of the cross sections at resonance, while the perturbative results diverge.

 

Keywords: Resonant laser- field; Electron-impact excitation; Helium atom; Nonperturbative method; First Born approximation; Differential cross section.

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