Phase delays in $\omega-2\omega$ above-threshold ionization

TL;DR

This paper investigates phase and time delays in above-threshold ionization wavepackets using theoretical simulations, revealing deviations from common approximations and highlighting the influence of atomic potential range.

Contribution

It provides a detailed theoretical analysis of phase and time delays in strong-field ionization, comparing different models and emphasizing the role of potential range effects.

Findings

Significant deviations of ab-initio phase delays from strong-field approximation predictions.

Differences between short-range and Coulomb potentials in phase delay extraction.

Insights into the similarities and differences with one-photon ionization delays.

Abstract

Relative phases of atomic above-threshold ionization wavepackets have been investigated in a recent experiment [L. J. Zipp, A. Natan, and P. H. Bucksbaum, Optica \textbf{1}, 361-364 (2014)] exploiting interferences between different pathways in a weak probe field at half the frequency of the strong ionization pulse. In this work we theoretically explore the extraction of phase delays and time delays of attosecond wavepackets formed in strong-field ionization. We perform simulations solving the time-dependent Schr\"odinger equation and compare these results with the strong-field and Coulomb-Volkov approximations. In order to disentangle short- from long- ranged effects of the atomic potential we also perform simulations for atomic model potentials featuring a Yukawa-type short-range potential. We find significant deviations of the \textit{ab-initio} phase delays between different photoelectron pathways from the predictions by the strong-field approximation even at energies well above the ionization threshold. We identify similarities but also profound differences to the well-known interferometric extraction of phase- and time delays in one-photon ionization.