Signatures of laser photon energy in (e,2e) reactions in helium

The laser-assisted electron-atom ionization processes, called laser-assisted (e, 2e) reactions, play a very prominent role in many applied areas such as plasma heating, plasma confinement, high power gas lasers, gas breakdown. Electron-impact ionization of helium target in the presence of a linearly polarized laser field is investigated at low incoming energy in the second Born approximation and in the asymmetric coplanar geometry. The status of incident and scattered electrons in the external laser field is described by the nonrelativistic Volkov waves. The dressed state of the ejected electron is treated as a Coulomb-Volkov wave function. The laser polarization vector is taken to be parallel to the incident momentum of the projectile. The scattering amplitudes are performed by using the Sturmian basis. Numerical results show that the laser photon energy dependence of the angular distributions of the ejected electrons has a significant control on the (e,2e) reactions. With laser photon energy increasing the electron-electron interaction is strongly enhanced and the shape of the recoil peak remains unchanged. The structure of the triple differential cross section in the vicinity of resonances have been discussed. It is shown that higher order terms of the Born series of the scattering amplitude are negligible compared to the first terms at high laser frequencies