Attosecond physics phenomena at nanometric tips

Attosecond science is based on electron dynamics driven by a strong
optical electric field and has evolved beyond its original scope in
gas-phase atomic and molecular physics to solid-state targets. In this
review, we discuss a nanoscale attosecond physics laboratory that has
enabled the first observations of strong-field-driven photoemission and
recollision at a solid surface: laser-triggered metallic nanotips. In
addition to the research questions of rather fundamental nature,
femtosecond electron sources with outstanding beam qualities have
resulted from this research, which has prompted follow-up application in
the sensing of electric fields and lightwave electronics, ultrafast
microscopy and diffraction, and fundamental matter-wave quantum optics.
We review the theoretical and experimental concepts underlying
near-field enhancement, photoemission regimes and electron acceleration
mechanisms. Nanotips add new degrees of freedom to well known
strong-field phenomena from atomic physics. For example, they enable the
realization of a true sub-optical-cycle acceleration regime where
recollision is suppressed. We also discuss the possibility of
high-harmonic generation due to laser irradiation of metallic
nanostructures.