Based on the numerical solution of the full-dimensional time-dependent Schrödinger equation, we study the above-threshold ionization of atomic hydrogen by subpicosecond laser pulses at wavelengths ranging from 300 nm to 800 nm, in which regime substructures of the photoelectron energy spectra resulting from quantum interference are entangled with those induced by the Freeman resonance. By analyzing the time-dependent populations and ac Stark energy shifts of the relevant atomic levels, and observing the pulse intensity dependence and the pulse length evolution of the spectra, we clearly identify the origins of the substructures exhibited in the spectra.

• Received 16 December 2019
• Revised 30 March 2020
• Accepted 21 April 2020

DOI:https://doi.org/10.1103/PhysRevA.101.053417