Investigation Of Non-sequential Double Ionization Of Polyatomic Molecules Driven By Intense Laser Fields

The non-sequential double ionization?NSDI?in the intense laser field involves many physical processes,and the dynamic of electron-electron correlation displayed in them has also attracted much attention.From simple monatomic systems to complex polyatomic molecular systems,it is a great challenge for theoretical researches.Because molecules have the additional nuclear degrees of freedom and structural diversity than atoms,molecular dynamics in a strong laser field involves more physical phenomena.For example,the effects of two different symmetric molecular orbitals of N₂ and O₂ on NSDI were measured;the effects of molecular orientation,the coupling of electronic vibration states,and ring molecules with different structures on NSDI under strong field were studied.In order to better understand the physical processes of these microscopic particles,researchers have also developed several theoretical methods,such as numerical solution of the time-dependent Schr?dinger equation,classical ensemble method,semi-classical method,quantum Monte-Carlo method.Among them,the classical ensemble method is a common method for calculating strong field ionization.This method requires less computing resources and the results obtained are qualitatively consistent with the results of quantum calculations.In addition,it can provide clear physical images for easier analysis of electronic behaviors.In this paper,the classical ensemble method is used to study the dynamics of polyatomic molecular systems under intense laser fields.It is mainly divided into two parts:1)We investigated the dynamics of the double ionization of C₃H₆ molecules with different structures?propylene and cyclopropane?under the linearly polarized and bichromatic counterrotating circularly polarized laser fields.We studied the double ionization probability of two structures at different wavelengths.It was found that in1200 nm laser fields,NSDI occur in both the propylene and cyclopropane molecules,that is,the"knee"structure appeared,while this phenomenon did not occur in the 800nm laser field.Meanwhile,we have found that the probability of double ionization of propylene is several orders of magnitude higher than that of cyclopropane.Secondly,in order to further explain this interesting phenomenon,we selected the linear polarization and counter-rotating field with an intensity of 30 TW/cm² and a wavelength of 1200 nm to calculate the momentum distribution and energy trajectory of recollision for double ionized electrons.It was noticed that propylene molecule have more momentum distributions and energy trajectories of double-charged ions than cyclopropane molecule,which further proved that the"knee"structure of propylene molecule is more obvious than that of cyclopropane molecule.2)We studied the dynamics of NSDI of OCS molecule at different laser wavelengths and intensities.Firstly,we investigated the double ionization probability of OCS molecule in linearly polarized?LP?and circularly polarized?CP?fields at 800nm.Compared with the situation of CP field,it can be found that the"knee"structure appears in the double ionization curve under the LP field,and this phenomenon is consistent with the experimental measured results.Secondly,we calculated the double ionization probability of the OCS molecule in the LP field at 1200 nm and compared it with the case of 800 nm in the same field.It can be seen that the ionization probability at these two wavelengths has an intersection point,and when the intensity is lower or higher than the intersection point,the ionization mechanisms appearing at the two wavelengths are just opposite.This phenomenon is also explained by the trajectories of the associated electrons during the collision.