Strong-field ionization of two-center systems: nondipole signatures in multiphoton regimes

We analyze the high-frequency multiphoton ionization of the simplest diatomic molecule H2+ by solving the time-dependent Schrödinger equation. Comparison between the exact results and the results based on either the first-order nondipole approximation or the dipole approximation is presented. This reveals various discrepancies in the photoelectron distributions between the three approaches. Thus, it leads to the conclusion that neither approximation accurately describes the ionization process, at least for the given laser field parameters. Throughout the paper, the interplay between Cohen-Fano (two-center) interference and the nondipole effects is analyzed. This includes, for instance, the parabolic shape of the interference fringes resulting from the radiation pressure and the multiple-hump structure of multiphoton peaks.