Phase-of-the-Phase Electron Momentum Spectroscopy on Single Metal Atoms in Helium Nanodroplets

Magnesium atoms fully embedded in helium nanodroplets are exposed to two-color laser pulses, which trigger multiphoton above-threshold ionization (ATI). This allows exemplary study of 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, indicating the impact of the droplet on the concerted emission process. Phase-of-the-phase spectroscopy, however, reveals a marked loss in the 2 omega-omega 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.

Automated summary

Magnesium atoms embedded in helium nanodroplets were studied using two-color laser pulses, and it was found that the droplet environment has a significant impact on single electron propagation. The angle-resolved photoelectron spectra showed differences compared to free atoms, with scattering in the neutral helium environment causing an almost isotropic angular distribution. Moreover, the appearance of higher-energy electrons indicated the influence of the droplet on the emission process. Phase-of-the-phase spectroscopy revealed a loss in the phase dependence of the electron signal. A Monte Carlo simulation including laser-assisted electron scattering successfully reproduced the experimental spectra and provided insights into electron emission from disordered systems under strong fields.