Single-photon ionization of aligned H with near-ionization-threshold photon energy

Abstract

We study single-photon ionization of aligned H in a high-frequency low-intensity laser field. We focus on the cases where the laser frequency is near to or somewhat larger than the ionization potential of the target. The calculated photoelectron momentum distribution through numerical solution of time-dependent Schrödinger equation shows clear interference patterns. However, different from the cases of photon energy far larger than the ionization potential usually explored in experiments, the positions of interference maxima and minima for the present cases can not be explained by the interference of the electronic wave with the observed momentum between these two atomic centers of the molecule. By developing a theory model applicable for ionization of molecules in high-frequency laser field, we show that the Coulomb potential plays an important role in the momentum component of the emitting electronic wave near the nuclei, resulting in a remarkable shift of the interference pattern. A simple expression with Coulomb-modified momentum is obtained to predict the interference extrema, which gives suggestions for probing the structure and electron dynamics of the aligned molecule in single-photon ionization with lower photon energy.