High-Order Harmonic And Nonsequential Double Ionization In Strong Laser Field

The interaction between strong laser fields and matter has received wide attention.In recently years,the intensity of laser fields increases with the development of the laser technology which influences the exploration of interaction between strong laser fields and matter.As the intensity of the laser increased,a serious of new phenomena appeared,such as multiphoton ionization?MPI?,tunneling ionization?TI?,high-order harmonic generation?HHG?and nonsequential double ionization ?NSDI?.The HHG not only accelerates the development of non-perturbation theory,but also supplies a kind of coherent light with short wavelength.The NSDI will provide a simple electron-electron correlation model,which was a major impact on the formation of chemical bounds in the chemical reaction,the phenomenon of superconductivity,and the solid state properties.The interaction between strong laser fields and matter is the basis of the ultra nonlinear physical phenomena,and it also influences the exploration of molecule structure,facilitates the development of imaging technology,and lays the foundation for the observation and control of the molecule chemical reactions.Using the theory to simulate the experimental observation,we studied the observation of atoms and molecules in the strong laser fields,and the conclusion are dram as follows:?1?The change of cutoff energy is explained by comparing the high harmonic spectra of atoms and molecules in various laser fields.Then the influence of ionization suppression on the high-order harmonic generation of the N₂?comparing atom Ar?and O₂?comparing atom Xe?were studied.Finally the influence of the molecular alignment on HHG were investigated.?2?Using a complete classical theoretical model,the non-sequential double ionization of Xe atoms were simulated.First of all,we studied the fast and low electron momentum distribution of Xe atom.It shows that the electrons are mainly emitted in the same direction.By changing the laser field,we found that the electron distributions from the process of recollision-induced ionization?RII?won't change,while the electron distributions from the process of recollision-induced exciation with subsequent ionization ?RESI? change.