Investigation Of Non-sequential Double Ionization Of Triatomic Molecules?CO₂?CS₂? In Intense Laser Fields

The nature of double ionization processes of atoms and molecules has both practical and fundamental interest because it provides a particularly clear manner to study the electron-electron correlation,which is responsible for the structure and the evolution of large parts of our macroscopic world.Comparing to atoms,due to diverse molecular structure and additional nuclear degree of freedom,molecules exhibit much more complicated processes in strong-field ionization.Obviously,investigating the ionization of molecules would show more abundant physics phenomena.Firstly,by using classical ensemble method,we investigate the non-sequential double ionization of CO2 molecule at different laser wavelengths.The numerical results show that the correlated behavior of the two electrons from NSDI are drastically different for the two wavelengths at comparatively low laser intensity,which indicates that under the low laser intensity,long wavelength can limit the complex ionized behaviors of CO2 molecule.On the contrary,under the high laser intensity,long wavelength will result in recollision excitation with subsequent ionization(RESI).The responsible electron dynamics of NSDI at 800 nm and 1600 nm is explored by analysis of the electron trajectories.Secondly,we investigate the double ionization mechanism of CO2 molecule and Kr atom in linearly polarized laser fields by the classical ensemble method and compared them together.The numerical results show that the probability for NSDI of Kr atom is higher than that of CO2 molecule.Our numerical calculations reveal that this different phenomenon is closely related to the Coulomb focusing effect: Coulomb potential will attract the returning electron more dramatically when it moves near the atomic or molecular core.For CO2 molecule,the returning electron is dramatically attracted by three cores,so the returned electron of CO2 molecule possesses higher energy than Kr atom does.Finally,by using two-dimensional Monte-Carlo classical ensemble method,we investigate the double ionization process of CS2 molecule with different bond lengths in an 800-nm intense laser field.The double ionization probability presents a “knee” structure with equilibrium internuclear distance R = 2.9245 a.u..As the bond length of C-S increases,the double ionization probability is enhanced and the “knee” structure becomes less obvious.In addition,the momentum distribution of double ionized electrons is also investigated,which shows the momentum mostly distributed in the first and third quadrants with equilibrium internuclear distance R = 2.9245 a.u.As the bond length of C-S increases,the electron momentum becomes evenly distributed in the four quadrants.Furthermore,the energy distributions and the corresponding trajectories of the double-ionized electrons versus time are also demonstrated,which show that the bond length of C-S in CS2 molecule plays a key role in the DI process.