The investigation of strong-field light-matter interactions is increasingly being applied to surfaces and nanostructures. Local enhancement and sub-wavelength confinement facilitate highly nonlinear optics in tailored optical near-fields. Using ultrashort pulses at visible and near-infrared frequencies, metallic nanotips have been shown to allow for enhanced nonlinear photoelectron emission confined to nanometric volumes; numerous effects regarding strong-field emission and carrier-envelope sensitivity were recently identified [1-3]. Currently, there is increasing interest in the impact of spatial inhomogeneity on electron dynamics in nanoscale systems[4]. Here, we investigate localized photoelectron emission from single gold nanotips with ultrashort laser pulses at near- and mid-infrared frequencies. We observe localized optical field emission throughout a wavelength range from 800 nm to 8 μm. The emission is found to be polarization sensitive, and photoelectron energies of hundreds of electronvolts are recorded. Simulations within a two-step photoemission model reveal that the dynamics are governed by the spatial confinement of the driving field. The talk will disseminate these recent results [5,6] and will present novel applications in time-resolved electron imaging based on such localized electron sources.
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