Observation of laser-assisted electron scattering in superfluid helium

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 create nano-structured systems consisting single atom or molecule surrounded by superfluid He shell variable thickness (32-340 angstrom). We observe generated femtosecond strong-field ionization core particle, can gain several tens photon energies due to multiple processes within liquid shell. Supported Monte Carlo 3D elastic simulations, these results provide first insight into interplay gain/loss dissipative movement liquid. Condensed-phase creates new possibilities space-time studies solids real-time tracing electrons liquids.