Comment on Elimination of Polarization Dependence from Optical Excitation Functions

The measurement of optical excitation functions excited by electron impact is typically accomplished by recording fluorescence emitted into a small solid angle perpendicular to the incident electron beam. This measured intensity is not proportional to the emission cross section due to target alignment, and a linear polarizer is typically oriented at the ``magic angle'' ($54.7^\circ$) with respect to the incident electron beam in order to eliminate this polarization dependence [1]. Existing literature for the derivation of the value for the magic angle assumes the polarizing element is ideal. A simple expression for this angle that accounts for the use of a partial polarizer is presented. [1] P.N. Clout and D.W.O. Heddle, J. Opt. Soc. Am. \textbf{59}, 715 (1969).