Coherent Control of Relativistic Electron Dynamics in Plasma Nanophotonics

Femtosecond laser pulses, amplified to ultrahigh intensities, can driveelectrons in solids to relativistic energies via collective motion, paving theway for miniaturized particle accelerators and powerful extreme-ultravioletlight sources. However, precisely controlling the space-time properties ofthese ultra-fast electrons on sub-femtosecond timescales remains a formidablechallenge due to the complex nature of interaction at such extreme fields.Here, we present a novel approach to coherently control the local fields onsub-femtosecond timescales at the interface between vacuum and a spatiallystructured plasma generated from a periodic array of dielectric nanopillars. Weexperimentally demonstrate and theoretically explain that such control offields enables enhanced acceleration and steering of relativistic electrons ina desired direction. Furthermore, our simulations predict the coherentformation of sub-femtosecond electron bunches from the nanopillars. Ourresearch brings nanophotonics to the realm of strong-field plasma physics andrepresents the enabling advancement for in-situ control of high-energyparticles, paving the way for novel applications in plasma technology.