Investigation Of The Autler-Townes Splitting And Wavepacket Motion Of Four-level Ladder K₂ Molecule In Intense Femtosecond Field

With the development of laser technology,more experimental and theoretical researches are about the study on the dynamic process of atoms or molecules in an ultra-fast laser field.The ultra-short and ultra-strong laser pulse is used to manipulate Autler-Townes?AT?splitting,wave packet motion,and the selective distribution of states of molecules.This is not only a hot topic of laser-matter interaction studies,but also an important topic of molecular dynamics research.Due to the high requirements of the experiment,it is of great significance to study the dynamic process of interaction between the intense laser field and matter theoretically.In this paper,the quantum time-dependent wave packet method is used to study the photoelectron spectra,wave packet motion and state population of the four-level ladder K₂ molecules by a three-color femtosecond laser field in order to explore the conditional methods of controlling wave packet motion in the three-color laser field.The main work includes the following aspects:?1?Using the four-state model and the time-dependent wave packet approach,the effects of the delay time and the pump wavelength in a femtosecond pump-pump-probe laser field on the photoelectron spectra of four-level ladder K₂ molecules were investigated.Focusing on the resonant laser field: the two cases of the delay time between the two pump lasers and the delay time between the second pump laser and the probe laser were studied.At the same time,the effect of delay time on peak shift and AT splitting was quantified for the first time.?2?Using the four-state model and the time-dependent wave packet approach,the effects of delay time and pump wavelength in a femtosecond pump-pump-probe laser field on wave packet motion and state population of four-level ladder K₂ molecules were studied.The results show that the wave packet performs periodic motion on both excited potential energy surfaces.The motion period decreases with the increase of the pump wavelength,and the amplitude of the wave packet also decreases with the increase of the pump wavelength.The delay time and pump wavelength cause the change of Rabi oscillation,and the change of Rabi oscillation leads to the periodical change of the ground state X,the excited state A and the excited state 2.Delay time and pump wavelength also affect the structure,position,and relative height of the peaks in the photoelectron spectra.Theoretically quantifying the influence of these parameters on the population of excited states can not only verify the periodical change rule,but also indicate that the parameters of the laser field can be regulated to control the wave packet motion and the selective distribution of states.The research results of this dissertation can provide some basis for the experiment to complete the optical control and quantum control process of the molecule,and provide a basis for further study of the dynamic characteristics of molecule system similar to the K₂ molecule.