  In conditions where the interaction betweeen an atom and a short
high-frequency extreme ultraviolet laser pulse is a perturbation, we show that
a simple theoretical approach, based on Coulomb-Volkov-type states, can make
reliable predictions for ionization. To avoid any additional approximation, we
consider here a standard case : the ionization of hydrogen atoms initially in
their ground state. For any field parameter, we show that the method provides
accurate energy spectra of ejected electrons, including many above threshold
ionization peaks, as long as the two following conditions are simultaneously
fulfilled : (i) the photon energy is greater than or equal to the ionization
potential ; (ii) the ionization process is not saturated. Thus, ionization of
atoms or molecules by the high order harmonic laser pulses which are generated
at present may be addressed through this Coulomb-Volkov treatment.
