  This paper concerns the theory of non-recollisional ionization or detachment
of atoms or ions by intense few-cycle pulses. It is shown that in certain
conditions of pulse duration, peak intensity and carrier-envelope phase, the
ionization probability integrated over ejection angle varies almost
periodically with energy, with a period roughly equal to the photon energy for
slow enough outgoing electrons. This modulation is found both in calculations
based on the strong field approximation (SFA) and in ab initio time-dependent
calculations. It is explained as resulting from the interference between the
contributions of different saddle times of the modified classical action.
Methods for efficiently calculating the SFA ionization amplitude beyond the
usual saddle point approximation are also discussed.
