Above-threshold ionization and photoelectron spectra in atomic systems driven by strong laser fields

TL;DR

This paper develops an analytical extension of the Strong Field Approximation to describe above-threshold ionization in atoms, enabling detailed analysis of re-scattering processes and their dependence on atomic and laser parameters.

Contribution

An analytical model extending SFA to include direct and re-scattering amplitudes, allowing detailed study of ATI processes and comparison with numerical solutions.

Findings

Good agreement between SFA and TDSE results for ATI spectra

Re-scattering processes depend on atomic and laser pulse features

Model captures phase dependence of photoelectron spectra

Abstract

Above-threshold ionization (ATI) results from strong field laser-matter interaction and it is one of the fundamental processes that may be used to extract electron structural and dynamical information about the atomic or molecular target. Moreover, it can also be used to characterize the laser field itself. Here, we develop an analytical description of ATI, which extends the theoretical Strong Field Approximation (SFA), for both the direct and re-scattering transition amplitudes in atoms. From a non-local, but separable potential, the bound-free dipole and the re-scattering transition matrix elements are analytically computed. In comparison with the standard approaches to the ATI process, our analytical derivation of the re-scattering matrix elements allows us to study directly how the re-scattering process depends on the atomic target and laser pulse features -we can turn on and off contributions having different physical origins or corresponding to different physical mechanisms. We compare SFA results with the full numerical solutions of the time-dependent Schroedinger equation (TDSE) within the few-cycle pulse regime. Good agreement between our SFA and TDSE model is found for the ATI spectrum. Our model captures also the strong dependence of the photoelectron spectra on the carrier envelope phase of the laser field.