Sub-barrier Coulomb effects on the interference pattern in tunneling ionization photoelectron spectra

TL;DR

This paper investigates how Coulomb interactions during tunneling affect interference patterns in photoelectron spectra, revealing shifts in interference fringes and nodal structures, with analytical and numerical validation.

Contribution

It introduces a semi-classical method to incorporate sub-barrier Coulomb effects, demonstrating their impact on interference patterns beyond traditional models.

Findings

Sub-barrier Coulomb effects shift intra-cycle interference fringes.

Analytical expressions for fringe shifts in the long-wavelength limit.

Good agreement with ab initio solutions, standard models fail.

Abstract

We use a quantum trajectory-based semi-classical method to account for Coulomb interaction between the photoelectron and the parent ion in the classically forbidden, sub-barrier region during strong-field tunneling ionization processes. We show that---besides the well-known modification of the tunneling ionization probability---there is also an influence on the interference pattern in the photoelectron spectra. In the long-wavelength limit, the shift of the intra-cycle interference fringes caused by sub-barrier Coulomb effects in the laser polarization direction can be derived analytically. We compare our results with \emph{ab initio} solutions of the time-dependent Schr\"odinger equation and find good agreement in the long-wavelength regime, whereas the standard strong field approximation fails. We show that the nodal structure along low-order above-threshold ionization rings is also affected by sub-barrier Coulomb effects.