Real-time evolution of a laser-dressed Helium atom: Attosecond-resolved two-color photoionization study

TL;DR

This study uses attosecond pulses and femtosecond lasers to observe and analyze the real-time dynamics of Helium atom ionization under strong laser fields, revealing quantum interference effects and resonance-mediated transitions.

Contribution

It provides the first real-time measurements of laser-dressed Helium atom ionization dynamics with attosecond resolution, combining experimental data with Floquet theory interpretation.

Findings

Observation of transitions between ionization channels during laser ramp-up

Extraction of quantum phases of interfering ionization paths

Validation of Floquet formalism in describing strong-field photoionization

Abstract

Using extreme-ultraviolet attosecond-pulse-trains, we investigate the photoionization dynamics of a Helium atom in the presence of moderately-strong (~10^12 W/cm^2) femtosecond laser pulses. The electronic structure of a laser-dressed atom is traced in real-time through precision measurements of ion-yields and photo-electron angular distributions. Quantum interferences between photo-excitation paths are interpreted using the Floquet formalism. As the laser pulse intensity ramps on femtosecond timescales, we observe transitions between ionization channels mediated by different atomic resonances. The quantum phase of interfering paths is extracted for each channel and compared with simulations. Our results elucidate photoionization mechanisms in strong-fields and open the doors for photo-absorption/ionization control schemes.