Polarization measurements for the3pPo3and4dD3terms of neutral helium excited by the beam-tilted-foil interaction

Polarization measurements have been made as a function of foil-tilt angle for the He I transitions $2s{}_{}{}^3{}_{}{}^{}S-3p{}_{}{}^3{}_{}{}^{}P_{}^o{}_{}{}^{}\left(3889\mathrm{} \AA \right)$ and $2p{}_{}{}^3{}_{}{}^{}P_{}^o{}_{}{}^{}-4d{}_{}{}^3{}_{}{}^{}D\left(4471\mathrm{} \AA \right)$. Particular attention was paid to the systematic effects that can enter into the analysis of such data from the decreasing time resolution as the foil-tilt angle is increased. It is shown that particle scattering at the foil is the main source of systematic error, but that this error can be eliminated by appropriate analytic techniques. The forms of the variation of the relative Stokes parameters with tilt angle are found to be very similar to those previously found for the corresponding singlet transitions, although the magnitudes of the alignment and orientation parameters are generally different for the singlets from the values we find for the triplets. The present results for $3p{}_{}{}^3{}_{}{}^{}P_{}^o{}_{}{}^{}$ are shown to be reasonably consistent with those recently published by Burns et al., provided that the necessary correction for decreasing time resolution at high tilt angles is included.