Plateau in Above-Threshold-Ionization Spectra and Chaotic Behavior in Rescattering Process

An improved quasistatic model is used to describe the ionization process of atoms in intense linearly polarized fields. Numerical calculations of Above-Threshold-Ionization (ATI) energy spectra and photoelectron angular distributions (PAD) of hydrogen atoms reveal clearly plateau and side lobe structures, which are in good agreement with recent ATI experiments. Our results show that, the existence of this plateau and side lobes is consequences of the classical kinematics of the electrons in combined atom and laser fields. Furthermore, we find that the onset of these unusual phenomena is related to the onset of the chaotic behavior in the system.