  Physical mechanisms of electron emission from fibre optic nanotips, namely,
tunnelling, multi-photon, and thermionic emission, either prevent fast
switching or require intense laser fields. Time-resolved electron emission from
nano-sized sources finds applications ranging from material characterisation to
fundamental studies of quantum coherence. We present a nano-sized electron
source capable of fast-switching (<1 ns) that can be driven with low-power
femtosecond lasers. The physical mechanism that can explain emission at low
laser power is surface plasmon enhanced above-threshold photoemission. An
electron emission peak is observed and provides support for resonant plasmonic
excitation. The electron source is a metal-coated optical fibre tapered into a
nano-sized tip. The fibre is flexible and back illuminated facilitating ease of
positioning. The source operates with a few nJ per laser pulse, making this a
versatile emitter that enables nanometrology, multisource electron-lithography
and scanning probe microscopy.
  Keywords: fibre optic nanotip, surface plasmon resonance, multi-photon
emission, above-threshold emission
