Stabilization Of Atoms Under High-frequency Intense Laser Fields

Over the past decades, laser intensities have increased by more than six orders of magnitude, up to 1022W/cm2. Such laser pulses give rise to a number of interest-ing novel effects, which could not be understood within the traditional perturbative framework. For example, the perturbative theory predicts that the atom ionization probability steadily increases with the the laser intensity. But the perturbative theory is apt to break down as the laser intensity becomes higher. And the direct nonpertur-bative handling of the Schrodinger equation has led to a counter-intuitive result:the higher the intensity, the lower the ionization probability, which is termed stabilization phenomenon.The two forms of atomic stabilization, i.e., the quasistationary stabilization and the dynamic stabilization have been identified theoretically. In our thesis, the phase-space averaging method is applied to investigate the stabilization of atomic hydrogen and the singly negatively charged hydride ion. Moreover, the Kramers-Henneberger(KH) effective potential derived from Dirac equation has also been studied in detail.The topics we have discussed in this thesis are listed as follows:Firstly, we investigate the stabilization of H and H-by using the phase-space averaging method. By calculating the ionization probabilities under different laser pulses, we find that the bound state of the hydrogen behaves more stable under high-frequency, linearly polarized laser fields with the slowly rising and descending edge. The ionization of the singly charged hydride ion is suppressed under the high-frequency short pulse.Secondly, though the Kramers-Henneberger (KH) transformation and high-frequency approximation, the time-dependent Dirac equation in high-frequency intense laser fields can be transformed to a time-independent equation with an effective Coulom-b potential, which plays an important role in studying the adiabatic atomic stability problem in high-frequency laser fields. With numerical calculation, we have investi-gated in detail the characteristics of this effective Coulomb potential. It is shown that when the laser intensity is high enough, the relativistic effect is so important that it modifies the effective potential drastically. Moreover, the dipole approximation of the laser field, which is often used in literature, is not valid for high-frequency laser fields.