Measurement of Integrated Stokes Parameters for He 3 ³P State Excited by Spin-Polarized Electrons

Integrated Stokes parameters P_i (i=1,2, 3) for the He 3 ³P → 2 ³S₁ (388.9nm) 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.