Ivestigation Of The Autier-Townes Splitting And Wavepacket Motion Of Three-level Ladder K₂ Molecule In Intense Femtosecond Field

The rapid development of ultra-short and ultra-intense laser technology has promoted theoretical and experimental researches on laser interaction with matter. Thereinto, controlling Autler-Townes?AT?Splitting, wave packet motion and state population transfer of atoms or molecules by using ultrashort laser pulses is not noly the important contents of laser interaction with matter but also the hot subject of molecular dynamics. In this thesis, the effects of intense pump-probe laser fields parameters on the photoelectron spectra?including the AT splitting?, wave packet movement and state populations of the three-level ladder K₂ molecule driven by intense femtosecond pump-probe pulses were investigated via employing the time-dependent quantum wave packet approach in order to explore the conditions and methods for controlling the channel selection of AT splitting, wave packet motion and state population transfer in two-color laser field. The main works are as follows.?1? We theoretically investigated the effects of laser intensities andwavelengths on the AT splitting in the photoelectron spectra of three-level ladder K₂ molecule driven by an intense femtosecond pump-probe pulses via employing the time-dependent quantum wave packet approach when delay time is zero. We discussed the characteristics of AT splitting for three cases: a resonant region, near resonant region and far-off resonant region, and firstly quantified these effects on peak shift and AT separation by using an analytical fitting function.?2? We theoretically investigated the effects of pump wavelength and pulse width on the wave packet movement of three-level ladder K₂ molecule driven by an intense femtosecond pump-probe pulse via employing the time-dependent quantum wave packet approach when delay time is not zero?1800 fs?. The results show that wave packet moves periodically on the excited state potential surface, and the period of wave packet does not vary with pump wavelength, while the oscillating amplitude decreases with increasing pulse width. Because wave packet motion can lead to the change of photoelectron spectra and state populations, we further study the effects of delay time, pump intensity,pump wavelength and pulse width on the photoelectron spectra and state populations. The result shows that the periodic motion of wave packet results in the periodic variation of photoelectron spectra. There is no AT splitting for weaker pump intensity or shorter pulse width. Delay time and pump wavelength can affect peak structure, position, and relative height.The Rabi oscillation is affected by delay time, pump intensity, pump wavelength and pulse width, and its variation results in the periodic change of the populations of the ground state and the excited state.Quantifying their effects on the population of the excited state verifies the periodical change regulation and shows that the change frequency varies with increasing pump intensity and pulse width. The results can provide some important basis for realizing the optical control and quantum manipulation of molecule experimentally. And provide some references for further studying the dynamics properties of atoms or molecules similar to K₂ molecule.