Keldysh approach to calculating the ionization rate in strong two-color fields
Phys. Rev. A 113, 013512 – Published 8 January, 2026
DOI: https://doi.org/10.1103/rmdz-fdls
Abstract
We extend the celebrated Keldysh approach to obtain closed analytical expressions for the ionization rate in strong optical fields to the case of the driving field, containing the fundamental frequency and its second harmonic, which are orthogonaly polarized to each other. In this situation, the separation of the tunnel and multiphoton regions is governed by two Keldysh parameters. Interference of the inter-frequency cross-terms contributing to the ionizationm is discussed. Whereas in the multiphoton regime the ratio of intensities of the fundamental and second harmonics plays an important role, in the tunneling limit, the ionization rate becomes nearly independent of this ratio and therefore of the driving wave shape.
