Polarization of Lyman-$\alpha$ Radiation Emitted in Electron Collisions with Hydrogen Atoms and Molecules

The polarizations of Lyman-$\alpha$ radiation produced (i) by electron impact on atomic and molecular hydrogen and (ii) by electric field quenching of metastable $2S$ hydrogen atoms have been measured. The polarization analyzer was a LiF crystal set at the Brewster angle, with reflected radiation being detected by an iodine-vapor photon counter. Generally good agreement between the measured polarization fractions and recent theoretical predictions was found. The radiation produced by quenching metastable atoms in an electric field was found to be polarized with a polarization fraction of -0.30±0.02, which compares with the theoretical value -0.323.