Lorentz meets Fano spectral line shapes: A universal phase and its laser control

TL;DR

This paper introduces a universal phase formalism linking Fano and Lorentzian spectral line shapes, experimentally demonstrating laser control of these profiles and enabling quantum-phase analysis in spectroscopy.

Contribution

It presents a novel universal temporal-phase formalism that maps Fano asymmetry to a phase, validated through experiments transforming line shapes with laser pulses.

Findings

Fano lines can be transformed into Lorentzian lines using laser pulses.

Lorentzian lines can be converted into Fano profiles, demonstrating reversibility.

The formalism enables extraction of quantum phase information from spectral line shapes.

Abstract

Symmetric Lorentzian and asymmetric Fano line shapes are fundamental spectroscopic signatures that quantify the structural and dynamical properties of nuclei, atoms, molecules, and solids. This study introduces a universal temporal-phase formalism, mapping the Fano asymmetry parameter q to a phase {\phi} of the time-dependent dipole-response function. The formalism is confirmed experimentally by laser-transforming Fano absorption lines of autoionizing helium into Lorentzian lines after attosecond-pulsed excitation. We also prove the inverse, the transformation of a naturally Lorentzian line into a Fano profile. A further application of this formalism amplifies resonantly interacting extreme-ultraviolet light by quantum-phase control. The quantum phase of excited states and its response to interactions can thus be extracted from line-shape analysis, with scientific applications in many branches of spectroscopy.