Polarization of Light Resulting from the Excitation of Helium by Electrons

Abstract

The polarization of light resulting from the excitation of helium by electrons was measured as a function of the bombarding electron energy. The wavelengths of the light whose polarization was measured are as follows: $\ensuremath{\lambda}=4713 \AA{} (4^{3}S\ensuremath{\rightarrow}2^{3}P)$, $\ensuremath{\lambda}=4922 \AA{} (4^{1}D\ensuremath{\rightarrow}2^{1}P)$, $\ensuremath{\lambda}=3188 \AA{} (4^{3}P\ensuremath{\rightarrow}2^{3}S)$, $\ensuremath{\lambda}=5876 \AA{} (3^{3}D\ensuremath{\rightarrow}2^{3}P)$, $\ensuremath{\lambda}=4388 \AA{} (5^{1}D\ensuremath{\rightarrow}2^{1}P)$, $\ensuremath{\lambda}=5016 \AA{} (3^{1}P\ensuremath{\rightarrow}2^{1}S)$, $\ensuremath{\lambda}=4471 \AA{} (4^{3}D\ensuremath{\rightarrow}2^{3}P)$, $\ensuremath{\lambda}=3889 \AA{} (3^{3}P\ensuremath{\rightarrow}2^{3}S)$. The polarization curves for the different wavelengths were measured for different pressures of the helium gas, and for $\ensuremath{\lambda}=4922 \AA{}, 4388 \AA{}, \mathrm{and} 5016 \AA{}$, there is a marked pressure dependence. There is a decided discrepancy between the theory as summarized by Percival and Seaton and the experimental results presented in this paper. No resolution of this discrepancy is given at this time.