Origin of the multiphoton-regime harmonic-generation plateau structure

Authors

Jean Marcel Ngoko Djiokap, University of Nebraska-LincolnFollow
Anthony F. Starace, University of Nebraska-LincolnFollow

ORCID IDs

J. M. Ngoko Djiokap https://orcid.org/0000-0003-4702-3544

Document Type

Article

Date of this Version

2020

Citation

PHYSICAL REVIEW A 102, 013103 (2020)

DOI: 10.1103/PhysRevA.102.013103

Comments

©2020 American Physical Society

Abstract

A physical interpretation is provided for the formation of the multiphoton-regime plateau feature in the spectra of nonlinear and correlated process of high-order harmonic generation (HHG) of two-active-electron atoms interacting with an intense linearly polarized laser field [Phys. Rev. A 88, 053412 (2013) for beryllium]. While in the strong-field tunneling regime the plateau feature is well known to be due to rescattering effects of the freed electron, its counterpart in the multiphoton regime is due to atomic resonance effects involving both singly excited states and doubly excited states. Here, we propose a strategy to uncover which kind of these states are responsible for this phenomenon. By studying the sensitivity of HHG to the initial state in helium, we show that this multiphoton-regime plateau structure mostly originates from singly excited states.