The Influence Of The Initial Electron Population Of Atoms And Molecules On The Strong Field Ionization

Non-linear phenomena such as high-order harmonic generation,non-sequential double ionization caused by the interaction of the strong laser field with atoms and molecules can be explained by the“semi-classical”model:The electrons are ionized by tunneling or over the barrier,then the ionized electrons oscillate with the laser field and have the opportunity to return to the parent ion to recombine or scatter.The ionization behavior irradiated by the laser field is the basis of these nonlinear phenomena,which is great significance to the study of the ionization mechanism and the ionization process.The initial state of the research system is usually the ground state,the electron's velocity also approaches zero at the ionization time.With the development of the experimental technology,the initial state of the system can be effectively controlled,and electrons have the opportunity to gain a larger velocity or a larger spatial population.Atomic and molecular ionization process with such an initial state in the strong laser field is the research content of this article,which includes the following three parts specifically:Firstly,by using the fully classical theoretical scheme,the ionization process of Xe atoms with initial angular momenta L(28)1 and L(28)-1 in the circularly polarized laser field is researched.It is found that the ionization yield of the atom whose electronic initial rotation direction is opposite to the laser electric field is significantly higher than that of the atom whose electronic initial rotation direction is the same as the laser electric field.With the driving laser wavelength,the ionization yield of the atom whose electronic initial rotation direction is opposite to the laser field decreases gradually,and the ionization yield of atoms whose electronic initial rotation direction is the same as the laser field increases gradually.Through the classical simulation and electron trajectory analysis,it is found that the variation of ionization yield with driving wavelength and the initial electronic rotation direction can be attributed to the coincidence probability of the bound electrons and the over the barrier exit formed by the laser field and the atomic potential.Moreover,the ionization process of atoms with different initial angular momenta in the circularly polarized chirped pulse is simulated.With the chirp coefficient increases,the ionization yield of the atom whose electronic initial rotate direction is opposite to the laser field decreases gradually,and the ionization yield of the atom whose electronic initial rotation direction is the same as the laser field increases gradually.Secondly,the double ionization process of Ar atoms with initial state total angular momenta L(28)1and L(28)-1in the circularly polarized laser field is studied.It is found that the double ionization yield of the initial state atoms with different angular momenta as the function of the driving laser intensity all show a more obvious"Knee"structure.In the laser intensity dominated by the non-sequential double ionization mechanism,the double ionization yields of the atom with initial angular momenta L(28)-1 is significantly higher than that of the atom with initial angular momenta L(28)1.By using the electron trajectory analysis,it is found that this difference in double ionization yield comes from the angle distribution between the electronic momentum and the force of the laser field at the single ionization time.When the initial state electronic rotation direction is opposite to the laser field,the ionized electron has a larger angle,and it is easier to return to the parent ion in a shorter time to recollision.In addition,the frustrated double ionization of Xe atoms with initial angular momenta L(28)1and L(28)-1 in the left-handed circularly polarized laser field is studied.It is found that the frustrated double ionization curve of Xe atoms with different angular momenta as the function of the laser intensity can be observed the obvious"Knee"structure.The frustrated double ionization yield of the atom with initial angular momenta L(28)-1 is significantly higher than that of the atom with initial angular momenta L(28)1.By analyzing the electron trajectory,it is found that the bound electrons in the frustrated double ionization of the atom with the initial angular momentum L(28)-1are more likely to reach a higher Rydberg state.Thirdly,the double ionization process of hydrogen molecules in the high intensity linearly polarized and in the co-rotating two-color circularly polarized laser field is studied.The double ionization mechanism of hydrogen molecules dominate by sequential double ionization in the high-intensity linearly polarized laser field,but its electron momentum correlation spectrum shows obvious"correlation"behavior.Back analyzing of the electron trajectory reveals that this correlation behavior does not cause from the recollision process,but the ultra-fast ionization of the molecules in a quarter cycle.In addition,the momentum correlation behavior of electrons is strongly dependent on the internuclear distance,so molecular structure information can be detected based on this correlation behavior.The double ionization yield of the hydrogen molecules can be observed with a clear"Knee"structure with the laser intensity in the larger range of the amplitude ratiog_E in the two-color co-rotating circularly polarized laser field.The proportion of non-sequential double ionization in the double ionization yield exhibits an oscillating behavior with amplitude ratiog_E.Back analyzing of electron trajectory reveals that this ionization behavior can be attributed to the instant change of ionization probability and the depletion effect of the ground state of the system.