  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.
