Dynamic Properties Of Eu 4f⁷6p_1/2ns Autoionization Process

It is well known that autoionization spectrum only represents total cross section of autoionization process,while the partial cross section and differential cross section of autoionization may provide more detailed information about autoionization process,such as identification of its final ionic states,the ratio of different decay paths and phase of the wave function.Therefore,to perform a systematic study on the branching ratios and the angular distributions of autoionization process may not only enrich the knowledge about the spectral structure of the Eu autoionizing states,but also explore the dynamical characteristics of autoionization process.The autoionization branching ratios of ions and the angular distributions of ejected electrons from the Eu 4f76p1/2ns(n=7,9)autoionizing states are investigated with the combination of the three-step isolated-core excitation and the velocity-map imaging techniques experimentally.Firstly,the Eu 4f76sns Rydberg states are populated via a two-step laser excitation,from which the Eu 4f76p1/2ns autoionizing states are excited by scanning the wavelength of the third laser around the Eu 6s+?6p+1/2 ionic resonance.Secondly,both the energy distribution of ejected electrons are acquired from their velocity-map images.Finally,the spectra of the branching ratios and the anisotropic parameters within the entire autoionization resonances are also demonstrated to study their energy dependence with correlation autoionization spectra.In addition,the possibility of the population inversion of ions are also discussed.When the velocity imaging technology is used,the polarization directions of the three lasers are controlled to parallel to each other,respectively,and the directions are parallel or perpendicular to the direction of detector,in order to control each transition of the magnetic quantum number.Obviously,when the polarization direction of the three excitation are parallel to the direction of the detector,the three step transition satisfies the selection rule of?M=0.When the polarization direction of the three excitation are perpendicular to the direction of detector,the three step transition satisfies the selection rule of ?M=±1.The branching ratio and the anisotropic parameters of 4f76p1/2ns(n=7,9)autoionization states in different polarization modes are also discussed and analyzed in this paper.