Circular Polarization of Impact Radiation Produced by Polarized Electrons in Mercury

Polarization measurements of nonresonant radiation produced by impact excitation of mercury atoms by polarized electrons are reported. In particular, the circular polarization of the transition $7{}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}\to 6{}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$ (404.7 nm) is presented as a function of electron energy. At excitation threshold, the polarization predicted by theory has been confirmed while above threshold the polarization is strongly affected by resonances. Connections with the role of the atomic interactions in the excitation process and with electron polarimetry are discussed.