Low-energy peak structure in strong-field ionization by mid-infrared laser-pulses: two-dimensional focusing by the atomic potential

TL;DR

This paper investigates the low-energy peak in strong-field ionization spectra, revealing it to be a classical focusing effect influenced by the atomic potential, supported by both classical and quantum simulations.

Contribution

It demonstrates that the low-energy structure in ionization spectra is primarily classical in origin, caused by two-dimensional focusing in the energy-angular momentum plane.

Findings

The low-energy peak correlates with high angular momenta of photoelectrons.

Quantum simulations support the classical focusing explanation.

Parameter dependencies match experimental observations.

Abstract

We analyze the formation of the low-energy structure (LES) in above-threshold ionization spectra first observed by Quan et al.\ \cite{quan09} and Blaga et al.\ \cite{blaga09} using both quasi-classical and quantum approaches. We show this structure to be largely classical in origin resulting from a two-dimensional focusing in the energy-angular momentum plane of the strong-field dynamics in the presence of the atomic potential. The peak at low energy is strongly correlated with high angular momenta of the photoelectrons. Quantum simulations confirm this scenario. Resulting parameter dependences agree with experimental findings \cite{quan09,blaga09} and, in part, with other simulations \cite{liu10,yan10,kast11}.