Laser-assisted ionization-excitation of helium by electron impact at large momentum transfer

Ionization of a helium atom by electron impact in the presence of laser radiation is studied theoretically. The kinematic regime of high impact energy and large momentum transfer is considered. The S-matrix of the process is treated within the first Born and binary-encounter approximations. Triple differential cross sections are calculated for the cases when the residual He+ ion is left both in the ground (n = 1) and in the first excited (n = 2) states in the presence of a laser field with frequency omega = 1.55 eV and intensity I = 5 x 10(11) W/cm(2). The laser-assisted cross sections corresponding to n = 2 are found to be more sensitive to the electron-electron correlations in helium than the field-free ones.