Study On Spectra And Dynamic Properties Of Eu 4f~76pns Autoionizing States

In recent years,laser spectroscopy has made a considerable progress in atomic spectroscopy,especially on the autoionizing states of alkaline-earth and rare-earth atoms.Studying autoionizing states of rare-earth atoms is not only helpful to inertial confinement fusion?ICF?,but also useful for development of new type ion laser,such as the Ba⁺laser based on autoionization.During the last few years,there have been reports on the autoionzation spectra of the Eu 4f⁷6p_1/2ns^[10]and Eu 4f⁷6p_1/2nd states,most of which are obtained with the ICE technique.On the other hand,for the lowest n members of the 6pns autoionzation series,the ICE technique becomes invalid to some extent,due to the interference effect between the two outermost electrons.Based on the above facts,this paper tries to find out the differences between the autoionization spectra with the ICE and the RIS techniques.To fulfill such a study,some excitation schemes without the ICE technique are adopted to maximize the interference effect between the two outermost electrons,while configuration interaction?CI?may make the autoionization spectra even more complicated.The spectra and dynamic properties of Eu 4f⁷6pns?n=7,8?autoionizing states are studied systematically with the resonance-ionization spectroscopy?RIS?and the velocity-map imaging?VMI?techniques.The RIS technique is utilized to obtain the spectra of Eu 4f⁷6pns?n=7,8?autoionizing states with the three-step excitation:the wavelengths of the first two-step lasers are fixed,while that of the last-step laser is scanned around the region of the 4f⁷6pns?n=7,8?autoionizing states.The VMI technique is used to detect the dynamic process of autoionization,from which the branching ratio?BR?of ions and the angular distribution?AD?of ejected electrons from Eu 4f⁷6p7s autoionizing states are achieved.The heavy configuration interaction is observed in the spectra of Eu 4f⁷6pns?n=7,8?autoionizing states,measured with RIS spectroscopy technique.The present study reveals the profound variations of AD and BR with energy in the region of the 4f⁷6p7s autoionization resonance,highlighting the complicated nature of the autoionization process for the lowest member of Eu 4f⁷6pns autoionization series.Population inversion is observed by analysis of the BR,while the validity of the well-known isolated core excitation?ICE?technique used for obtaining autoionization spectrum is discussed.In this paper,the spectral information of 4f⁷6pns?n=7,8?autoionizing states of Eu atom has been investigated with RIS technique.The energy dependence and variations with the total angular momentum J are studied.Moreover,because the Eu ground state is degenerated,the total angular momentum of the autoionizing states are difficult to identify with the different laser polarization combinations.Meanwhile,the AD and BR of ejected electrons from 4f⁷6p7s autoionizing states are observed by VMI technique.It is found that the 4f⁷6p7s autoionizing states mainly decay to the 4f⁷6s⁺?⁹S^o?and 4f⁷6s⁺?⁷S^o?ionic states.There is a population inversion in the energy region 55630-55670cm^-1 between 4f⁷6s⁺?⁹S^o?and 4f⁷6s⁺?⁷S^o?ionic states.