Time of flight-photoemission electron microscope for ultrahigh spatiotemporal probing ofnanoplasmonic optical fields

Abstract

Nanoplasmonic excitations as generated by few-cycle laser pulses on metal nanostructuresundergo ultrafast dynamics with timescales as short as a few hundred attoseconds (1 as = 10−18 s). So far, the spatiotemporal dynamics of optical fields localized on the nanoscale(nanoplasmonic field) have been hidden from direct access in the real space and timedomain. An approach which combines photoelectron emission microscopy and attosecondstreaking spectroscopy and which provides direct and non-invasive access to thenanoplasmonic field with nanometer-scale spatial resolution and temporal resolution of theorder of 100 as has been proposed (Stockman et al 2007 Nat. Photon. 1 539). To implementthis approach, a time of flight-photoemission electron microscope (TOF-PEEM) with∼25 nm spatialand ∼50 meV energy resolution, which has the potential to detect a nanoplasmonic field withnanometer spatial and attosecond temporal resolution, has been developed andcharacterized using a 400 nm/60 ps pulsed diode laser. The first experimental resultsobtained using this newly developed TOF-PEEM in a two-photon photoemission modewith a polycrystalline Cu sample and an Ag microstructure film show that the yield andthe kinetic energy of the emitted photoelectrons are strongly affected by the nanolocalizedplasmonic field.