Computation of the ac Stark effect in the ground state of atomic hydrogen

Using a Sturmian function expansion we have computed the nth order coefficients ${\mathrm{E}}_{\mathrm{n}}$(ω), for 2≤n≤22, in the perturbation expansion of the ac Stark effect in the hydrogen 1s state. An ‘‘effective convergence’’ similar to that in the dc case is observed. A parametrization of these coefficients, based upon the analytic structure of the Coulomb Green’s function, separates the rapid oscillatory resonant behavior and the smooth background variation with respect to ω.