Ionization Of Atom And Molecule In Intense Laser Fields

Recently, owing to the rapid advancement of laser technology, the interaction of intense laser fields with atoms and molecules has been the subject of many theoretical and experimental investigations. We can approach the regime where the laser field interaction with electron far exceeds the binding energy of the valence electrons. In this case, many interesting phenomena of excitation and photoionization can be observed, for instance, muti-photon ionization, above threshold ionization, tunnel ionization and so on. We study ionization behavior of atom and molecule exposed to an intense laser field in this thesis. The major investigations are listed as follows:Firstly: Considered the volume effects of laser, the ion production of some noble gases and their ions have been calculated by using ADK model in the tunneling regime. Compared the present results with the BSI model and experimental results, it is found that the results by the ADK model become better along with the increase of atomic number. Especially for Xe ions, it can give very good results without intensity shift. It gives a conclusion that the ADK model can be given better results for ion production of heavy atoms (or ions) than ones of the BSI model. Finally, analyzing the applicability of the ADK model, we can also obtain the same conclusion as the numerical results.Secondly: Calculated the ionization rate of N2, CO and O2 by using MO-ADK model in the tunneling regime, and analyzed the variety of ionization rate when the molecular axis is in different angle with the field direction. Our results demonstrate that the ionization rate of diatomic molecules would not be largest when the molecular axis is lined up with the field direction. It is relative to the electron density. For aσorbital, the ionization rate is the largest because of the initial electronic cloud is aligned with the molecular axis, but for aπorbital, the ionization rate is small because of the initial electronic cloud is preferentially aligned in a direction perpendicular to the molecular axis.Thirdly: Time-dependent density functional theory is formulated via the time- dependent Kohn-Sham equation. Solving time-dependent Schr?dinger equation and Kohn-Sham equation of three-dimensional atom in intense laser fields with split-operator method and using the window-operator technique, we obtain electron energy spectra for atomic hydrogen and helium. Then we compare photoelectron spectrum of hydrogen to the results of Chen et al who obtained by exactly solving time-dependent Schr?dinger equation. According to our study, we find that the two methods can give the same results.