The Two-Photon Nondipole Transition Phases across the Cooper Minima and Resonant States

Beyond the widely adopted dipole approximation, nondipole effects play an important role in completely understanding the electronic dynamics in light-matter interaction. We present a two-photon interferometric scheme to theoretically study the under-threshold nondipole transition phase over a broad energy range. It is found a significant difference between the nondipole and dipole two-photon transition phases near the Cooper minimum, which originates from the multichannel interference in the nondipole transition. Through the angular dependence of transition phase, we uncover the competition among partial waves in nondipole ionization. This work advances the fundamental understanding of nondipole dynamics in two-photon ionization, and opens a route toward the complete reconstruction of nondipole photoelectron wave packets.