Nonadiabatic Tunneling Of Photoelectrons Induced By Few-Cycle Near-Fields

Our work investigates strong-field processes in the vicinity of nanostructures with a characteristic size of around 100 nm. In particular, we use 7 fs laser pulses at 80 MHz from a Ti: sapphire femtosecond laser oscillator to excite localized surface plasmons on different gold nanoparticles. Such nanoparticles can localize the light field to nanometric volumes, while also enhancing the field strength. We determine the enhancement by measuring the kinetic energy spectrum of the electrons that are photoemitted from the surface of the nanoparticle as a function of incident laser intensity [1] , [2] . From the shape of the energy spectra, and the retrieved field enhancement values, we are able to follow the transition between two regimes: the first is characterized by multiphoton emission [MPE], while in the second (at higher intensities), tunneling [TE] of the electrons through the potential barrier distorted by the laser field is more pronounced. There have been studies of these two emission regimes for select systems, but little is known about the transition region between them, the so-called non-adiabatic tunneling.