Resonance ionization of atoms in a strong spatially inhomogeneous electromagnetic field

An investigation is made of the influence of spatial inhomogeneity of the electromagnetic field on the process of resonance ionization of atoms. It is shown that the result of averaging over the spatial distribution of the field depends on the "initiating" mechanism for formation of a dispersion dependence of the ionization probability on the radiation frequency. For all known initiating mechanisms, analytic expressions are derived to determine the line profile of the dispersion curve in a spatially inhomogeneous field having a Gaussian distribution over the transverse coordinate. It is found that if the extreme value of the energy shift of the transition due to the dynamic Stark effect$\alpha F^2_0$ is greater than the width of the dispersion curve in a homogeneous field, allowance for spatial inhomogeneity results in additional broadening of the dispersion curve, its actual order-of-magnitude width being $\alpha F^2_0$.