Phase-of-the-phase electron momentum spectroscopy on single metal atoms in helium nanodroplets

TL;DR

This study investigates how helium nanodroplets influence electron emission from embedded magnesium atoms under laser pulses, revealing scattering effects and phase dependence loss through spectroscopy and simulations.

Contribution

It introduces phase-of-the-phase spectroscopy combined with Monte-Carlo simulations to analyze electron dynamics in a neutral medium, highlighting medium-induced scattering effects.

Findings

Electron angular distributions become isotropic due to scattering.

Higher energy electrons are observed, indicating droplet impact.

Loss of phase dependence in electron signals is detected.

Abstract

Magnesium atoms fully embedded in helium nanodroplets are exposed to two-color laser pulses, which trigger multiphoton above-threshold ionization (ATI). This allows to exemplarily study the contribution of a dense, neutral and finite medium on single electron propagation. The angular-resolved photoelectron spectra show striking differences with respect to results obtained on free atoms. Scattering of the individual Mg photoelectrons, when traversing the neutral helium environment, causes the angular distribution to become almost isotropic. Furthermore, the appearance of higher energy electrons is observed, pointing out the impact of the droplet on the concerted emission process. Phase-of-the-phase spectroscopy, however, reveals a marked loss in the \2ww phase dependence of the electron signal. Taking into account sideband formation on a quantitative level, a Monte-Carlo simulation which includes laser-assisted electron scattering can reproduce the experimental spectra and give insights into the strong-field-induced electron emission from disordered systems.