The impact of nonessential states in near-resonant two-photon ionization of hydrogen*

By numerically solving the three-dimensional time-dependent Schrodinger equation, two-photon ionization of hydrogen is investigated at the near-resonant frequencies of the 1s-2p transition. Due to the Rabi oscillations between the 1s and 2p states, the photoelectron energy spectrum exhibits the Autler-Townes (AT) doublet and we focus on its spectral characteristics. Developing a minimal three-level model that is fully supported by the accurate 3D TDSE simulations, we demonstrate the role of the ac Stark shifts and the nonresonant ionization pathway in the energy splitting, asymmetry and angular distribution of the lower and higher energy peaks of the AT doublet. Furthermore, we show how these spectral features can be controlled with the actual choice of the laser parameters (Phys. Rev. A 106, 063114, 2022).