Alignment of helium excited by thin carbon foils

Abstract

We have measured the linear polarization of the 5016-Å, $2s{}_{}{}^1{}_{}{}^{}S-3p{}_{}{}^1{}_{}{}^{}P$ transition of Hei excited by a thin carbon foil perpendicular to the incident ${\mathrm{He}}^{+}$ beam at ion energies 50-500 keV. We find that the alignment of the $3p{}_{}{}^1{}_{}{}^{}P$ term depends upon the beam current density within the range (2-150 μA ${\mathrm{cm}}^{-2\mathrm{}}$) measured. Oscillations in the dependence of both $\frac{M}{I}$ (the linear polarization fraction) upon energy and the current density variation of $\frac{M}{I}$ with energy are observed. We discuss possible origins of these variations.