Observation of pure resonance and threshold effects in electron impact experiments in high intensity laser fields

This report describes experiments which were aimed to: (1) observe induced one photon free-free transitions associated with electron scattering by rare gas atoms in a CO2 laser field; (2) observe resonances in the free-free channel under experimental conditions when direct scattering is eliminated (by making the electric polarization vector and the momentum transfer vector perpendicular to each other). We have detected free-free transitions associated with elastic scattering by Ar and Xe at 141 and 90 deg scattering angles, respectively, using incident electron energies near resonances. Resonances in the elastic channel were readily observed for He, Ar and Xe but due to poor statistics, we were not able to demonstrate the resonances in the free-free channels. There was indication, however, that (in agreement with the soft photon approximation) the free-free direct scattering amplitude was zero when the laser polarization direction was perpendicular to the momentum transfer direction. On the basis of our studies, it was concluded, that (although the aims described above could be achieved with our apparatus) it would require much more time, than presently is available to us, to demonstrate the effects with proper signal to noise conditions.