Local time dependence of the magnetic sublevel population and polarization of fluorescence radiation

We investigate the time-dependence magnetic sublevel population and polarization of x-ray photoemission for the 1s2p ³ P _2,1 → 1s ^{2 1} S ₀ lines of an exemplary ion Fe²⁴⁺ due to impact excitation by a longitudinally polarized electron beam. The analysis is performed based on the fully relativistic distorted-wave approximation and the magnetic sublevel-to-magnetic sublevel collisional-radiative model. The radiative cascade process and Breit interaction are considered to make the results more precise. The time evolution of the magnetic sublevel populations and circular polarization properties are discussed. Our results reveal for the first time that the variations of the magnetic sublevel populations demonstrate a pattern when the time is shorter than 10³ ps; some of the populations increase rapidly, while the others remain relatively constant. These dramatic influences also bring about notable changes in the polarization properties of fluorescence emission. We compare our results with other theoretical predictions and find good consistency. This work provides new insight into the fundamentals of x-ray radiation and further prompts the application of fluorescence polarization in plasma diagnostics. (paper)