Effect of cascade transitions on the polarization of light emitted after electron-impact excitation of Zn by spin-polarized electrons

Abstract

We investigate the possible effect of cascade transitions from the $(4s5p)\phantom{\rule{0.16em}{0ex}}{}^{3}{P}_{0,1,2}$ states to the $(4s5s)\phantom{\rule{0.16em}{0ex}}{}^{3}{S}_{1}$ state of Zn. The polarization of the light emitted in the subsequent decay to the $(4s4p)\phantom{\rule{0.16em}{0ex}}{}^{3}{P}_{0,1,2}$ states has been the subject of recent controversy, with significant disagreement between the experimental data reported by Pravica et al. [Phys. Rev. A 83, 040701 (2011)] and by Clayburn and Gay [Phys. Rev. Lett. 119, 093401 (2017)] in the cascade-free region below $\ensuremath{\approx}7.6$ eV incident energy and relatively good agreement above. The cross sections for excitation of the $(4s5p)\phantom{\rule{0.16em}{0ex}}{}^{3}{P}_{0,1,2}$ states, as well as higher-lying triplet states, and the linear polarization of the cascade radiation seem too small to produce a significant alignment of the $(4s5s)\phantom{\rule{0.16em}{0ex}}{}^{3}{S}_{1}$ state, thereby raising additional questions regarding the origin of the relatively large linear polarizations measured above the cascade threshold.