Enhancement of ultrafast electron photoemission from metallic nanoantennas excited by a femtosecond laser pulse

We have demonstrated for the first time that an array of nanoantennas (central nanotips inside sub-micrometer pits) on an aluminum surface, fabricated using a specific double-pulse femtosecond laser irradiation scheme, results in a 28-fold enhancement of the non-linear (three-photon) electron photoemission yield, driven by a third intense IR femtosecond laser pulse. The supporting numerical electrodynamic modeling indicates that the electron emission is increased not owing to a larger effective aluminum surface, but due to instant local electromagnetic field enhancement near the nanoantenna, contributed by both the tip's 'lightning rod' effect and the focusing effect of the pit as a microreflector and annular edge as a plasmonic lens.