Detailed comparison of theory and experiment of strong-field photodetachment of the negative hydrogen ion

We study the strong-field interaction of a negative hydrogen ion in a short infrared laser pulse. An imaging technique is employed in a fast ion beam to record angular-resolved energy distributions of the photodetached electrons. The spectrum exhibits four excess photon channels. A detailed analysis of the energy and angular distribution is presented, including a comparison with recent theories. From our data we determine elastic-scattering phase shifts of the partial continuum waves in the lowest-order detachment channel. Quantitative agreement with scattering theory is obtained. A quantum interference effect predicted in a recent Keldysh-like theory is observed at energies close to threshold. We propose an analogy to a double-slit model which explains the interference features in a simple and intuitive way. We also verify the applicability of the Wigner threshold law in the strong-field regime and discuss its role in the observed quantum interference.