Theory of the Okorokov effect

A kinematical and a dynamical theory of the Okorokov effect are developed by time-dependent perturbation theory. The peak profile of the coherent resonant excitation is calculated in detail for ${\mathrm{He}}^{+}$ ions. We show that the peak profile changes very strongly for the various channeling conditions. In almost all cases the half-width of the peak is comparable with the difference of the higher harmonics position in the Okorokov condition.