The Classical Theoretical Investigation Of Ionization Dynamics Of Hydrogen And Nitrogen Molecules In Intense Laser Fields

In recent years, the dynamics of atoms and molecules in intenselaser fields plays an important role in the strong-field physics. Manynovel phenomena of atoms and molecules in intense lasers field had beenfound, including sequential double ionization (SDI), charge resonanceenhanced ionization (CREI), the high-order harmonic generation andnon-sequential double ionization(NSDI). The single ionization,sequential ionization and charge resonance enhanced ionization can becalculated by the single-active-electron approximation, because inthose conditions the interaction between electrons can be neglected.However, it is not the case for NSDI. Since the electron correlationplays an important role in the NSDI process, which cannot be calculatedby the single-active-electron approximation. As an outstandingmanifestation of electron-electron correlations in intense laserfields, non-sequential double ionization of atoms and molecules inintense laser fields has continued to attract experimental andtheoretical attention. A widely accepted explanation to the NSDI isthe rescattering model proposed by Corkum. First, one electron tunnelsin the field, in then the ionized electron driven back to the parent ion by laser fields and exchange energy with the second one, if theenergy enough then both of the electrons will escape from nuclei.As one of simplest molecules H2has attract a lot of interest.Recent experimental investigation using nitrogen molecule and oxygenmolecule as targets suggest that there are a lot of differencesbetween varies molecular species. As mentioned above, the NSDI of atomsand molecule is resulted from the interaction between electrons andthe hallmark of this strong correlation is “knee” structure of thedouble ionization probability versus the laser intensity. In our paper,we will investigate the double ionization dynamics of nitrogenmolecule and hydrogen molecule for comparison. The physical mechanismof NSDI has been illuminated by means of the correlated electronmomentum spectrum. Besides, the electron yield of N2and H2is alsocalculated to obtain the further insight of molecular ionizationdynamics.In this paper,we have investigated the double ionization dynamicsof H2molecule and N2molecule in intense laser fields with theincreasing wavelength. The “knee” structure of NSDI is observed inH2molecule and N2molecule with the wavelength of532nm,800nm,1024nm and2000nm. The momentum distribution of final double ionizedelectron pairs is calculated to further interpret the NSDI mechanism.The momentum distribution predominantly lies in the first and third quadrants, which indicates NSDI. With the increase of the wavelength,the momentum distribution looks slimmer and mostly distributed in thefirst and third quadrants. Besides, we calculated the electron yieldof H2molecule and N2molecule at the end of pulse with the increasingwavelength. We can see the behavior of the direct and “rescattering”electrons, and the energy structure also demonstrates that the numberof electron with higher energy increases with the increasing laserwavelength. Moreover, we have investigated the double ionizationdynamics of H2molecule and N2molecule in circlar polarized intenselaser fields.In summary, we have investigated the double ionization dynamicsof H2molecule and N2molecule in intense laser fields with theincreasing wavelength. The “knee” structure of NSDI is observed inH2molecule and N2molecule with the wavelength of532nm,800nm,1024nm and2000nm. The momentum distribution of final double ionizedelectron pairs is calculated to further interpret the NSDI mechanism.With the increase of the wavelength, the momentum distribution looksslimmer and mostly distributed in the first and third quadrants.Besides, we calculated the electron yield of H2molecule and N2moleculeat the end of pulse with the increasing wavelength. We can see thebehavior of the direct and “rescattering” electrons, and the lowenergy structure also demonstrates that the number of electron with higher energy increases with the increasing laser wavelength.