Investigation Of Nonsequential Double Ionization Of Molecules Driven By Strong Laser Fields

Nonsequential double ionization (NSDI) in intense laser field not only includes rich physical process, but also reveals the effect of electron correlation in the interaction of matter and intense laser pulses. In order to know in detail the physical process and physical mechanism in NSDI, it is necessary to study the influence of various factors on NSDI. Compared to atoms, molecules have an additional freedom of nuclear distance. Though many investigations about the influence of nuclear distance on ionization probability have been carried out, there have no report about the effect of nuclear distance on electron correlation in NSDI so far. In addition, two-color laser field in an efficient tool to study and control NSDI, the influence of intensity ratio of two-color field on NSDI deserves undoubtedly careful study. Aim at the above two questions, the main contents of our work are:We investigate the influence of internuclear distance (R) on double ionization of H2 by three dimensional classical micro-canonical model. It is found that double ionization of H2 strongly depends on internuclear distance. (1)As R increases, double ionization (DI) probability of H2 increases first and the decreases, which reaches its maxima at about 4a.u.; (2) When molecule axis aligns perpendicular to the laser polarization, the enhancement of double ionization is more pronounced in the case of moderate fields;(3) The dependence of electron correlation in NSDI of H2 on R weakens as the angle between molecular and laser polarization (φ) increases. Whenφis zero, the NSDI of H2 for different R provides rich correlation patterns, for example, (e,2e) recollision, recollision excitation with subsequent field-ionization;Whenφisπ/2, the correlation pattern is similar for different R. (2) For perpendicular alignment and different laser intensity, These results are qualitatively explained by classical potential expression model and back analysis. These results indicate that molecular structure has important influence on NSDI of diatomic molecules.We investigate the dependence of NSDI of He and HeH+ on intensity ratio of orthogonal two-color fields. The correlated electron momentum distributions of He and HeH+ depend strongly on intensity ratio of two-color fields, and this dependence is related to relative phase (φ) of two-color fields. Whenφ=0.25π, with intensity ratio increasing, correlated momentum distribution along the polarization of long wavelength field translates from correlation to anticorrelation pattern; Asφincreases, correlated momentum distributions change slightly with the variation of intensity ratio, the correlated momenta are clustered in the first and the third quadrants, whenφis 0.457c, the correlation pattern of HeH+are asymmetric with respect to the diagonal px1+px2=0. Moreover, this asymmetry decreases with intensity ratio increasing. These results are explained based on the variation of recollision time, recollision angle and recollision energy with intensity ratio in NSDI. Furthermore, from the variation of recolision time and recollision angel with relative phase for a given intensity ratio, we known that orthogonal polarized two-color fields can be serve as an efficient tool to control the correlated electron dynamics in NSDI.