  The ionization of atomic hydrogen in intense laser fields is studied
theoretically. The calculations were performed applying both quantummechanical
and classical approaches. Treating the problem quantummechanically, the time
dependent Schr\"odinger equation (TDSE) of our system was first transformed
into a pseudo-momentum space and solved in this space iteratively. While
neglecting the Coulomb potential during the solution of the TDSE we got the
results in the Volkov approximation, in the first order solution we taken into
account the Coulomb potential as perturbation. The classical calculations were
performed within the framework of the classical trajectory Monte-Carlo (CTMC)
method.
  The double differential ionization probabilities are calculated for different
laser pulses and a reasonable agreement was found between the theories. Major
differences can be observed in the angular distribution of electrons at low
electron energies between classical and the quantummechanical approaches. At
high electron energies the differences disappear, which indicates that the
generation of low energy electrons is of quantum type, and it is strongly
influenced by the Coulomb potential, while the production of high energy
electrons is of classical type and it is less influenced by the Coulomb
interaction. Our results are also compared with the Coulomb-Volkov (CV) model
calculations.
