No abstract

We present linear and circular polarization measurements of 3 1 P-2 1 S' (501.6 nm) photons detected in delayed coincidence with electrons inelastically scattered from the 3^ level of helium. Vector polarization and coherence parameters of the coincident radiation provide direct experimental evidence of the coherent nature of the excitation process, Atomic orientation is obtained directly from the circular polarization measurements. Analysis of the data also yields A and x parameters for 3*P excitations, which are compared with previous data and theory.

For pt.I see ibid., vol.23, no.19, p.3373-92 (1990). A stepwise excitation electron-photon correlation experiment is presented in which a combination of electron-photon coincidence and laser excitation techniques is used. Atomic collision parameters were measured for the electron impact excitation of the Hg 61P0-61P. (185 nm) transition at 16 eV incident electron energy and for electron scattering angles in the range 5'-30'.

New data from a superelastic scattering experiment on e--Na atom collisions at 10, 15, 20, 25 and 30 eV incident energy are presented and compared with existing experimental data and theories based respectively on the distorted wave second-order Born approximation, 15 state close-coupling and coupled channel optical potential calculations. Overall, fair to good agreement is found between theory and experiments for individual atomic scattering parameters. The loss of coherence previously observed by some workers at small scattering angles (5-20 degrees ), is confirmed at 20 eV and also observed at 25 eV. This loss of coherence is poorly modelled by existing theories.