Tunneling Ionization Of Atom In Intense Laser Fields

The interaction between laser field and atoms and molecules has been one the hot topics in this field for over several decades. The development of laser technology, such as recently attosecond technology, opens a new window to deeply explore the physics of a particle suffered in intense laser fields. Tunneling ionization plays an important role to understand the ionization phenonmena in strong field. After briefly introduce the basic concepts and phenomenan of strong field, we investigate the tunneling ionization of hydrogen atom in intense laser felds using numerical simulation and analytical method respectively in this thesis.There are three parts in this thesis as follows:Firstly, we present the detailed derivation of the tunneling ionization rate of an atom in an intense laser field (ADK theory), which is a foundation theory in this field. In the case of weak field, the Wentzel-Kramers-Brillouin (WKB) semiclassical method is used to solve the stationary Schrodinger equation of hydrogen atom in the external electric field, and the tunneling rate is found. In this calculation, the initial wave function is approximated as the ground state of hydrogen atom with asymptotic coulomb interation.Secondly, we obtain the ionization rate of hydrogen atom in the tunneling regime by numerically solving the three-dimensional time-dependent Schrodinger equation (TDSE), and compare it with the result of the ADK theory. It is interesting to note that the ionization rate obtained by ADK theory is higher than the TDSE results, especially, in the region of relative high field. Furthermore, an analytic expression for tunneling ionization rate of hydrogen atom in a static electric field is derived by combining WKB approximation with higher order perturbation theory, which induces a polarization effect of the initial wave function by external electric field. The new formula shows a suppression effect on the ionization rate, compared with the convetional ADK tunneling formula, and well agrees with the result of TDSE. Our analysis shows that the polarization of the initial wave function makes the effective one-dimensional barrier broder and higher, therefore leads to a lower tunneling rate.Finally, the wavelength dependence for the ionization process of hydrogen atom in intense laser field is studied by the TDSE method. The ionization rates of hydrogen atom calculated under different frequencies and light intensities are compared with the previous published results. We also investigate the wavelength dependence of the electron dynamic in ionization precess. The oscillation of the occupation of bound states intends to be smoother and close to the case of static electric field with increasing wavelength, which indicates that the ionization goes deep into the tunneling regime. Moreover, the interference of electrons ionized in different optical periods is observed, which is more obvious with increasing wavelength.(We shall use atomic units h=e=m=1throughout unless otherwise indicated.)...