Investigation Of The Dynamics In High-order Harmonic Generation From The Atomic And The Small Molecular Systems

The rapid development of ultrafast laser technology provides a powerful tool to recognize the microscopic ultrafast dynamics,and the high-order harmonic generation,as one of the important nonlinear physical phenomenon in the interaction between the ultrafast laser pulse and the matter,makes it possible to monitor the ultrafast electron dynamics,which appeals numbers of researchers.Moreover,with the development of the laser technology,many new phenomena are found in the harmonic emission,such as the multiple rescatterings,harmonics from excited state,harmonic redshift and so on.Thus the related dynamic process should be further studied to improve the application value of the harmonics.In thesis,the multi-electronic-state model is established to consider the correlated effect of the electron and nuclear motion based on the non-Born-Oppenheimer approximation.The electron dynamics,electron-nuclear correlation dynamics and the dynamics of excited state in harmonic generation process from the atom and the small molecule with single electron are systematically investigated,moreover,the law and the characters of the harmonic emission are summarized and the distinct physical image are established to improve the research about the dynamics in harmonic emission in the strong laser field.The related investigations are as follows:(1)The electron dynamics in multiple rescattering processes of the helium atom in the homogeneous and inhomogeneous fields are investigated by solving the time-dependent Schr?dinger equation and the Newton equation.Not only is the law of the maximum energy of each rescattering summarized,but the physical image of the multiple rescatterings is established in both fields.Moreover,the intra-cycle interference is controlled with the superposition of the ground and the excited states,and the inter-cycle interfere is further manipulated by the combined field of the static electric pulse and the trapezoidal pulse;(2)The electron dynamics in multiple rescattering process is investigated with the model of hydrogen molecular ion.Not only is the physical image of the molecular multiple rescatterings established,but also the multiple rescatterings originating from the recombination with the parent ion and the neighbour ion are distinguished,respectively.Moreover,the multiple rescattering processes from the recombination with the neighbour ionare sensitive to the variation of the internuclear distance;(3)Based on the non-Born-Oppenheimer approximation considering the electron-nuclear correlation and the pump-probe scheme,the multi-electronic-state model is established to investigate the electron-nuclear correlation dynamics and the dynamics of the excited state in harmonic emission from the tritium molecular ion.Based on the two-electronic-state quantum model,the minimum is found in the higher-order harmonic spectrum which can be ascribed to the electron localization around one nucleus in the coupling region of the ground state and the first excited state.Furthermore,it encodes the electron dynamics of the excited state at the time of ionization.Based on three-electronic-state quantum model,the related physical image of the harmonic emission is established.By discussing the electron dynamics of the excited state with different populations,the harmonic redshift in the probe field with long wavelength can be mainly attributed to the second rescattering of the electron at higher excited state.Moreover,the manipulation of the second rescattering is proposed to further verify the mechanism.