Observation of laser-assisted electron scattering in superfluid helium

TL;DR

This paper reports the first observation of laser-assisted electron scattering (LAES) in superfluid helium, demonstrating energy transfer to free electrons in a condensed phase environment, which opens new avenues for studying electron dynamics in liquids.

Contribution

It provides the first experimental evidence of LAES in a superfluid helium environment, supported by simulations, revealing how electrons gain energy through multiple scattering processes in a liquid.

Findings

Electrons gain tens of photon energies via LAES in superfluid helium.

LAES occurs in condensed phase, previously only observed in gases.

Simulations support experimental observations of energy transfer mechanisms.

Abstract

Laser-assisted electron scattering (LAES), a light-matter interaction process that facilitates energy transfer between strong light fields and free electrons, has so far been observed only in gas phase. Here we report on the observation of LAES at condensed phase particle densities, for which we create nano-structured systems consisting of a single atom or molecule surrounded by a superfluid He shell of variable thickness (32-340 angstrom). We observe that free electrons, generated by femtosecond strong-field ionization of the core particle, can gain several tens of photon energies due to multiple LAES processes within the liquid He shell. Supported by Monte Carlo 3D LAES and elastic scattering simulations, these results provide the first insight into the interplay of LAES energy gain/loss and dissipative electron movement in a liquid. Condensed-phase LAES creates new possibilities for space-time studies of solids and for real-time tracing of free electrons in liquids.