Attosecond Probing of Nanoplasmonic Fields

Attosecond science (1as = 10-18 s) is based on steering electrons by the electric field of a laser pulse and on the subsequent recollision with the parent matter. Recent advances have extended attosecond science to nano-scale solid-state systems, opening up a new research field at the interface of surface science, ultrafast spectroscopy, nonlinear optics and nano-optics [1,2]. Photoemission from metallic nanotips has been shown to be extremely sensitive to the waveform of ultrashort laser pulses, hence enabling direct measurements of optical fields in amplitude and phase with nanometer and attosecond resolution [1].

Here we demonstrate sensing of plasmonic near-fields at nanostructures and macroscopic optical fields in free space. In a first study, we determine the magnitude of plasmonic field enhancement at metallic nanotips of different sizes and materials [3]. We are also able to resolve the phase shift of the near-field with respect to the incident far-field by comparing photoemission from nanotips to a reference experiment with a gas-phase target [4]. To the best of our knowledge, our study constitutes the first measurement of the attosecond time delay in the optical response of a nanostructure performed directly at the position of the plasmonic hotspot. We simultaneously achieve resolutions on the order of 100 as and 5 nm. This opens to door for imaging electron dynamics in plasmonic circuits at the spatio-temporal resolution frontier.

[1] M. Krueger et al., Nature 475, 78 (2011).
[2] M. Ciappina et al., Rep. Prog. Phys. 80, 054401 (2017).
[3] S. Thomas, M.K. et al., Nano Lett. 13, 4790 (2013).
[4] M. Krueger et al., manuscript in preparation (2018).