Simultaneous electron-photon excitation of helium in a CO2 laser field

The R-matrix Floquet method is used to study the electron-impact excitation of helium in the presence of a CO2 laser field, for collision energies between 19 and 21.5 eV and laser intensities of 10(7) and 10(8) W cm(-2). Collision geometries with the electron incident at various angles to the laser polarization axis are considered. The signal for the production of metastable states is in good agreement with the results of a low-frequency approximation and a semi-classical approach, while agreement with experiment is reasonable.