Electron rescattering at metal nanotips induced by ultrashort laser pulses

We investigate plateau and cutoff structures in photoelectron spectra from nanoscale metal tips interacting with few-cycle near-infrared laser pulses. These hallmarks of electron rescattering, well-known from atom-laser interaction in the strong-field regime, appear at remarkably low laser intensities with nominal Keldysh parameters of the order of greater than or similar to 10. Quantum and quasiclassical simulations reveal that a large field enhancement near the tip and the increased backscattering probability at a solid-state target play a key role. Plateau electrons are by an order of magnitude more abundant than in comparable atomic spectra, reflecting the high density of target atoms at the surface. The position of the cutoff serves as an in situ probe for the locally enhanced electric field at the tip apex.