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

J Phys Chem Lett. 2022 Feb 17;13(6):1526-1532. doi: 10.1021/acs.jpclett.2c00110. Epub 2022 Feb 8.

Abstract

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 2ω-ω 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.