Alternate Method of Measurement of the Polarization of Light Emitted by Helium Atoms Excited by Energetic Electrons

Previous measurements on the polarization of helium light emitted by atoms excited by an electron beam have resulted from the observation of the intensity of the light at right angles to the direction of the electron beam. Polarization was determined in terms of the relative intensities of the components of this light whose electric vectors were oriented parallel to and at right angles to the direction of the electron beam. Because of the disagreement between experiment and theory, an alternate method in which the angle $\theta$ between the line of observation and the electron beam could be altered was used. After correcting the effective volume of the reaction region observed, the total intensity of light at a given angle is related to that observed at 90° by the relationship, $I_{\theta }=I_{90}(1-\pi {cos}^2\theta )$, where $\pi$ is the polarization. Results given show that for $\lambda =4922\mathrm{}$ Å, relative changes of polarization with electron energy are similar to those observed with the previously described more sensitive method. The trend of the polarization toward zero at the onset of excitation was again observed.