Simultaneous Stokes parameter measurements of the electron impact excited helium 31D state

Stokes parameter measurements have been made of the decay radiation in an electron-photon polarization correlation study of the helium 3 1 D state. Small electron scattering angles q e between -40' and +20' were studied for an incident electron energy of 40 eV. The first efforts to simultaneously determine all three Stokes parameters from the analysis of the variation in the coincidence rate as a retarder is rotated in front of a fixed polarizer in the photon analyser are reported. Measurements of the linear polarization Stokes parameter P 2 and the circular polarization P 3 agree well with previous sequentially acquired, discrete angle measurements. However, a significant disagreement with previous results was observed for the linear polarization parameter P 1 .