A quasi-coincidence measurement of the polarization of radiation emitted from the 3³p state of fast helium atoms populated by He-He charge transfer collisions

Abstract

The circular and linear polarizations of photons emitted in the 2('3)S-3('3)P HeI transition have been measured. The 3('3)P state of fast helium atoms was populated by He('+)-He charge transfer collisions in the incident ion energy range from 2.5 to 4.0 keV. Radiation from the fast atoms was collected as a function of scattering angle by selecting scattered atoms with an angle-defining aperture. Comparison of the measured values of the Stokes parameters M/I and C/I with linear polarization data from true coincidence measurements enabled checks on possible systematic errors, as well as assessments of the effects of limited angular resolution and stray magnetic fields. Corrections for the cascading from higher levels based on related measurements were estimated. Measurement of the Stokes parameter S/I permitted a direct comparison with theoretical predictions of the magnitude of this parameter. Although limited in precision by uncertainties in several quantities associated with the analysis, the data appear to be in basic agreement with the predictions of this theory. These measurements provide useful information on the quasi-coincidence measurement method as applied to both ion-atom and ion-surface charge transfer coherence studies.