New data on the polarisation of helium lines excited by electron impact

Abstract

Data obtained in recent electron-photon coincidence experiments on helium excitation have been used together with differential cross section data to determine line polarisations independently of previous direct measurements. Polarisations have been determined at electron impact energies in the range 60-100 eV for the following lines: 2¹P-1¹S (58.4 nm), 3¹P-1¹S (53.7 nm) and 3¹P-2¹S (501.6 nm). Reasonable agreement is found with data from a recent experiment on the vacuum ultraviolet line polarisation of helium and with one experiment on the 501.6 nm line. The data are compared with recent theoretical predictions.