Paper: 2016 Nanofocused Plasmon-Driven Sub-10 fs Electron Point Source

Nanofocused Plasmon-Driven Sub-10 fs Electron Point Source

Reviews and Highlights Quantum Science Molecular and Soft-matter Ultrafast Nano-optics and Nanophotonics Mineralogy and Geochemistry

Melanie Muller, Vasily Kravtsov, Alexander Paarmann, Markus B. Raschke, and Ralph Ernstorfer
ACS Photonics 3, 611 (2016).

Progress in ultrafast electron microscopy relies on the development of efficient laser-driven electron sources delivering femtosecond electron pulses to the sample. In particular, recent advances employ photoemission from metal nanotips as coherent point-like femtosecond low-energy electron sources. We report the nonlinear emission of ultrashort electron wave packets from a gold nanotip generated by nonlocal excitation and nanofocusing of surface plasmon polaritons. We verify the nanoscale localization of plasmon-induced electron emission by its electrostatic collimation characteristics. With a plasmon polariton pulse duration less than 8 fs at the apex, we identify multiphoton photoemission as the underlying emission process. The quantum efficiency of the plasmon-induced emission exceeds that of photoemission from direct apex illumination. We demonstrate the application for plasmon-triggered point-projection imaging of an individual semiconductor nanowire at 3 μm tip?sample distance. On the basis of numerical simulations we estimate an electron pulse duration at the sample less than 10 fs for tip?sample distances up to a few micrometers. Plasmon-driven nanolocalized electron emission thus enables femtosecond point-projection microscopy with unprecedented temporal and spatial resolution, femtosecond low-energy electron in-line holography, and a new route toward femtosecond scanning tunneling microscopy and spectroscopy.