Study Above-threshold Ionization Of Atoms And Molecules By Using The Wave Function Splitting Method

With the rapid development of laser technology,researchers can use femtosecond laser and attosecond pulse to explore the internal structure of matter and its ultrafast dynamic process.Many interesting nonlinear optical phenomena of matters exposed to an intense laser field have attracted very wide attentions,such as high order harmonic generation(HHG),above-threshold ionization(ATI),non-sequential double ionization(NSDI)and so on.Above-threshold ionization is a very important research topic of strong field physics.Based on semi-classical theory,we study photoelectron spectra and momentum distribution of model atoms or molecules by solving the time-dependent schr(?)dinger equation(TDSE).The main contents of this thesis are as follows:(1)We study the dependence of above-threshold ionization energy spectra on the chirp rate of one-dimensional model hydrogen atom exposed to chirped laser field by numerically solving the time-dependent schr(?)dinger equation combined with the wave function splitting method.It is found that photoelectron energy spectra obviously depend on the chirp rate under multi-photon ionization and tunneling ionization mechanisms,while photoelectron energy spectra do not depend on the chirp rate in single-photon ionization regime.Further analysis shows that the chirp dependence of the multi-photon ionized photoelectron spectrum can be originated from the contribution of excited bound states.In the single-photon ionization region,the valence electron can be released by directly absorbing a single photon,thus the excited bound states play a less role.For tunneling ionization,the active electron have a certain probability to tunnel through the barrier,or it can be firstly excited to some intermediate bound states and then tunneling occurs.The dependence of photoelectron energy spectrum on the chirp rate is determined by the laser field and the excited bound state.(2)We systematically investigate the ellipticity,internuclear distance,carrier-envelope phase(CEP)and alignment angle depedences of photoelectron momentum distribution of two-dimensional model hydrogen molecule ion in the elliptically polarized laser field by solving the time-dependent schr(?)dinger equation combined with wave function splitting method.In the elliptically polarized laser field,the intensity of photoelectron momentum distribution increases with the increasing ofellipticity,the range of photoelectron momentum distribution also increases.Under the same ellipticity,we found photoelectron momentum distributions have certain dependence on internuclear distance which can be well understood by analyzing the initial photoelectron momentum distribution.There is almost no CEP dependence of intensity of photoelectron momentum distribution,however,the emission angle of photoelectron has a very strong CEP dependence.If the angle between the polarization direction of laser and molecular axis is not zero,photoelectron momentum distribution does not depend on the molecular alignment angle and always distribute vertically to molecular axis direction.