Anomalous Fano Profiles in External Fields

TL;DR

This paper investigates how external fields influence Fano resonances, revealing complex parameters and control mechanisms that modify spectral line shapes in photo-electron and absorption spectra, supported by computational and experimental comparisons.

Contribution

It demonstrates that external control fields induce complex Fano q-parameters and identifies specific control mechanisms affecting spectral line shapes.

Findings

External fields lead to complex Fano q-parameters.

Control pulses during excitation modify line shapes via momentum boosts.

Post-excitation pulses create interference fringes from two-photon transitions.

Abstract

We show that external control of Fano resonances in general leads to complex Fano $q$-parameters. Fano line shapes of photo-electron and transient absorption spectra in presence of an infrared control field are investigated. Computed transient absorption spectra are compatible with a recent experiment [C. Ott {\it et al.}, Science 340, 716 (2013)] but suggest a modification of the interpretation proposed there. Control mechanisms for photo-electron spectra are exposed: control pulses applied {\em during} excitation modify the line shapes by momentum boosts of the continuum electrons. Pulses arriving {\em after} excitation generate interference fringes due to infrared two-photon transitions.