Measurement of Integrated Stokes Parameters for He 33PState Excited by Spin-Polarized Electrons

Integrated Stokes parameters Pi (i = 1,2,3) for the He 3 3P→2 3S1 (388.9 nm) transition after excitation from the ground state to the 3 3P state by a transversely spin-polarized electron beam are measured in near threshold energy region. The experimental results are presented. The linear-polarization P2 are consistent with zero over the incident energy range, providing evidence for the LS coupling mechanism of the 3 3P state. The measured circular polarization P3 are non-zero, indicating strong electron-electron exchange effects in the spin-polarized electron-atom collision process.