Theoretical Study Of Momentum Distribution And Excited State Effects In Atomic Or Molecular Non-sequential Double Ionization In Intense Laser Fields

The ionization dynamics research of atomic or molecular in strong laser field is one of the field of physics research in recent years.The process of nonsequential double ionization(NSDI)is complex and profound,and there are a great deal of research and results of phenomena presented in the process of NSDI.In continuous learning and exploring,there are a lot of physical phenomena and problems to study and solve.Recent studies have found that there are several mechanisms in the process of NSDI,yet can not be sure the different mechnisms and the contribution of every mechanism in the process.On the basis of argon atom model,the article studies the method to observe the momentum distribution and shows the typical characteristics of two-electron momentum distribution of different NSDI mechanisms.Meanwhile,we investigate the difference of the phenomena in the two half-cycle for each laser cycle in the NSDI process of asymmetric molecules.And we expect that the excited stated have a great effect on the difference.In this paper,we introduce the NSDI mechanisms widely approved,and we use the"snapshot" method to observe the momentum distribution then investigate the mechanisms of NSDI of atoms as exposed to ultra-strong and ultra-fast laser fields through numerical and analytical simulations.We find that the range of the selected wave function influences significantly on the shape of the two-electron momentum distribution,and therefore affects remarkably on analyzing and studying the NSDI.On the basis of classical three-step model,we analyze the dynamics of correlated electron pairs in NSDI and find the applicable range of the selected wave function to observe two-electron momentum distribution.We analyze the dynamics of different NSDI mechanisms in detail,including the ionization of recollion-induced doubly excited states,the recollion-excitation with subsequent field ionization and the simultaneous emission upon rescattering.Then we show the typical characteristics of two-electron momentum distribution of different NSDI mechanisms,which give suggestions on experimental study of NSDI.With the help of two-electron momentum distribution,we study the effects of excited states on the strong-field ionization dynamics of asymmetric molecules.We investigate the dynamics of the one-dimensional asymmetric molecule HeH+ in strong laser field numerically without the use of Born-Oppenheimer(BO)approximation.Except being different from the dynamics of simulation with BO approximation,we show that the momentum distribution of double ionization is different in the two half-cycle for each laser cycle.Meanwhile,we compare R-dependent differential ionization probability of E(t)>0 and E(t)<0 for HeH+.And we expect that the excited states have a great effect on the difference.