We have measured the polarization state of the light emitted in the ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ I, $2s{}_{}{}^1{}_{}{}^{}S-3p{}_{}{}^1{}_{}{}^{}P$ transition after excitation in a beam-foil experiment and find a partial elliptical polarization which depends upon the tilt angle of the carbon foil relative to the beam axis. This indicates that the emergent beam is oriented as well as aligned as a result of an interaction at the foil surface. The relative excitation cross sections and off-diagonal density-matrix elements have been deduced for the angular-momentum sublevels.

• Received 4 February 1974

DOI:https://doi.org/10.1103/PhysRevLett.32.751