Benchmark of Few-Level Quantum Theory vs. ab initio Numerical Solutions for the Strong-field Autler-Townes Effect in Photo-Ionization of Hydrogen

The temporal and spectral consequences of an intermediate resonance en route to strong-field photoionization [1] are investigated theoretically in two ways: by solving few-level model equations and by ab initio numerical solution of the time-dependent Schrödinger equation, in both cases for hydrogen in three dimensions. The model is designed to include field-dressed atomic states via resonance in a three-level reduction of the hydrogen atom consisting of the 2p-3d (Balmer) transition and one energetically-distant continuum state. The model's level occupation probabilities are derived from three Schrödinger amplitude equations, and are benchmarked against the ab initio numerical solution under the same strong field. We examine contrasts between the results of the two approaches with a particular focus on Autler-Townes doublets [2] that appear in the photoelectron spectrum.

[1] P. Lambropoulos and X. Tang, "Resonances in Multiphoton Ionization", in Atoms in Intense Laser Fields, edited by M. Gavrila (Academic Press, Cambridge, 1992), p. 335.

[2] S. H. Autler and C. H. Townes, Phys. Rev. 100, 703 (1955).