Correlated Electron Momentum Distribution And Scaling Law Of Atomic Double Ionization In Strong Laser Field

Electron-electron correlation is a universal phenomenon in the microscopic world. It was a major impact in formation of chemical bounds in chemical reaction,the phenomenon of superconductivity, and the solid state properties, but also an important part of attosecond physics. Strong field non-sequential double ionization(NSDI) process provides a basic model for the study of electron-electron correlation,and became a frontier of the strong-field laser physics.In this paper, using the classical Monte Carlo method, the double ionization of rare gas atoms in intense laser field, we established a scaling law of double ionization,and tested the role of multiple collision by using few-cycle laser pulses of special envelope. The main contents of this thesis are as follows:(1) Illuminated by the scaling law in single ionization process, we proposed for the first time a scaling law of NSDI: the momentum distribution of the correlated electrons from an atom driven by a laser field of frequency ω and intensity I is the same as that from another atom irradiated by the laser field of frequency kω and intensity I.k3 The scaling ratio k equals to the ratio of the second ionization potentials of two atoms. With the momentum distribution of the correlated electrons, we firstly verify the cubic dependence of the laser intensity with the scale factor, and then determine the scaling ratio which is the ratio of the second ionization potentials between two atoms, and finally verify the scaling law can be applied to Ar, Ne, He and Mg atoms.(2) By means of the momentum distributions of the correlated electrons produced in recollision impact ionization process, we verified that the electron correlation is kept unchanged under the scaling transform. In the progress, the ionization time interval of two electrons is very short, so drift momenta that the electrons obtained form the laser field after ionization are almost the same. Hence, theelectron correlation encodes directly into the end-of-pulse momentum distribution of two electrons. This provides a straightforward way to study the electron correlation in NSDI. The scaling law states that, in order to get equivalent electron correlation effects, one should choose laser fields of equal ponderomotive parameter, and enlarge the laser frequency in linear proportion to the second ionization potentials of the target atoms.(3) We study double ionization of Ar atoms irradiated by few-cycle laser pulses of special envelopes, and focus on the role of multiple collisions between the ionized electron with the core. The laser pulses are of trapezoidal-shaped pulse envelope, and the cycle-resolved electron dynamics is obtained by increases the cycle number one-by-one. We find that, at a higher laser intensity, the correlated-electron momentum distribution in the three-cycle laser pulse exhibits two predominate structures in the first and the third quadrants. They are formed by the electron pairs in which the second electron is knocked out by the returning electron in the second cycle.As the pulse duration increases, more electron pairs accumulate in the second and the fourth quadrants of the momentum diagrams. In these electron pairs, the second electron is firstly excited owing to collision with the returning electron and then is ionized by the laser field. By varying the peak intensity, we find the momentum distributions transit from anticorrelation to correlation in three-cycle laser pulses,which disproves that multiple collision causes the transition.