Research Of Strong Field Atomic Double Ionization

Strong field nonsequential double ionization is widely concerned and studied for it contains the interaction between the two electrons.Because of the strong electron correlation,the double-ionization yield can be 6 or more orders of magnitude greater than the standard theory predicts.The electron correlation is also the main factor of many physical phenomena and the major subject of attosecond physics.Nonsequential double ionization of atom can provides a simple model for people to explore the microscopic dynamics of double ionization and the strong electron correlation.In this paper,using the classical ensemble method,we exhibit the knee structure in circle pulse laser fields for Ar and He atoms,test the role of multiple collision,find a way to get equal time intervals in different laser-atom systems,and research the effect of excited states in nonsequential double ionization.The main contents and achievements are as following:(1)Nonsequential double ionization of noble atoms in circle pulse is studied.By choosing laser fields according to a scaling law,we exhibit the knee structure in CP laser fields for Ar and He atoms.Through track the classical trajectorys of two electrons,we find that the electron recollision is universal in the CP laser fields,and the knee structure does exist for noble atoms.The ionization probability in the knee region decreases as the wavelength of the driving laser pulses increases.To observe the knee structure in the CP laser fields,it is beneficial to use target atoms with small ionization potentials and to use driving laser fields with short wavelengths.(2)Nonsequential double ionization of Ar atoms in intense few-cycle laser pulses is studied.By increasing the peak intensity in three-cycle laser pulses,we showed the transition of the CMDs from anticorrelation to correlation,which disproves that multiple collisions cause the transition.Moreover,we find that the RESI electrons becomes more notable with the increasement of optical cycles in laser pulse,but the RII electrons stays the same.(3)Using the classical simulation method,we study the time interval between emissions of two electrons from atoms.Equal time interval can be obtained from different laser-atom systems,provided that the frequency of the driving laser fields changes linearly with the ratio of the second IPs,while the intensity changes quadratically with the ratio.After the transform,the ponderomotive energy of the electrons in intense laser field keeps unchanged.This research has a lot of reference value in attosecond physics.(4)The effect of laser intensity in nonsequential double ionization of Ne atoms is studied.We show that,contrary to the general expectation,the RESI events take an increasing fraction in the NSDI events as the laser intensity increases.We distinguish the the RII and RESI processes via the back-trajectory technique,and find that the excited state play a key role in these processes through statistical research of electron energy.