Study On Ionization Property Of Diatomic Molecules In Intense Femtosecond Laser Field

It has been the focus of researchers to manipulate the real-time dynamic of atoms and molecules in theory and experiment,as the rapid development of femtosecond laser technology.Besides,using the femtosecond laser to study the control mechanism on a specific system is necessary.In this thesis,the ionization dynamics of Li2 molecule in intense femtosecond pulses is studied using the time-dependent quantum wave packet method.The Aulter-Townes splitting of four-level Li2 is studied by two pump and one probe femtosecond pulses via photoelectron spectra.The structure of the triple splitting is presented to analyze the information of selective population of dressed states.It was found that one can manipulate the population and energy of the dressed states by adjusting the laser intensity,three pulses' wavelength and the time delay.Rabi oscillation appears when the intensity of laser field reaches to 3×1011W/cm2,and three peaks arise along with the side peaks moving away when we increase the intensity to 4.5×1011W/cm2.Thus we can control the population and energy of dressed states by regulating the laser intensity.The peak value of the right side is the highest when the positive detuning of pump-1 is more than 25 nm,while the left peak is the highest when the negative detuning is greater than 45 nm,and the peaks shift to lower energy as increasing pump-1 wavelength.So we can control population and energy of three dressed states with regulating the pump-1wavelength.With the increase of detuning degree of pump-2 pulse(positive detuning reaches to 50 nm or negative detuning reaches to 45nm),three peaks change to two peaks which is explained using doubly dressed states.Besides,peaks in photoelectron spectra move to lower energy with the increase of pump-2 wavelength.Therefore,population and energy of dressed states can be manipulated by changing the wavelength of pump-2 pulse.The degree of three peaks splitting is not affected by probe pulse,which only influences the peaks' position.Thus energy distribution of the dressed states can be regulated by the probe wavelength.Two side peaks disappear gradually when we increasing the delay time between pump and probe pulse,and the side peaks disappear completely when the delay time reaches to 20 fs.Hence we can manipulate the population of dressed states.Our results are instructive for the control of chemical reactions and the study of reaction mechanisms.