Simultaneous electron-photon excitation of He 23S: an experimental investigation of the effects of laser intensity and polarisation

Laser assisted electron excitation of the 23S state of helium is examined at electron energies near to the threshold for excitation in the field of a pulsed CO2 laser delivering ∼108 W cm-2 in the scattering region. The simultaneous electron-photon excitation cross section of helium is studied at various laser intensities and at different angles between the laser polarisation and the incident electron beam. These data are a first step towards elucidating the influence of various scattering parameters on this complex process and are compared with the results of recent calculations. (author)