A brief survey of the experiment on electronic excitation of atoms, carried on at the Atomic Beam Group of the Lawrence Radiation Laboratory, is made.By means of alignment of excited atoms by electron-impact excitation, we first observed rf paramagneticresonance reorientation of Hg and neon metastable states.Later on, the method was extended to observe the coherence property of excited atoms associated with the electron-impact excitation.The coherent excitation of nondegenerate levels of excited atoms results in intensity beats either in the fluorescent decay due to spontaneous radiation or in the resonance absorption by a long-lived metastable state.
Detailed information is given on an experiment which we have reported previously, studying intensity beats in the resonance absorption due to nondegenerate magnetic sublevels of the
3P2 mercury metastable state coherently excited by electron impact. Rather straightforward theory is used to explain the experimental result. It is found that regardless of the exciting energy, as long as there is sufficient selective excitation of certain magnetic sublevels, the absorption beat frequency is modulated at twice the Larmor frequency when the incident electron beam is perpendicular to the externally applied field
H0 and the linearly polarized monitoring light is perpendicular to the electron beam.