Plasmonic amplification of free-electron evanescent fields

TL;DRAbstract

We show experimentally for the first time that free-electron evanescent fields can be amplified by a plasmonic nanolayer in a manner analogous to the way in which optical fields are amplified in the poor-man's superlens.<br/> <br/>The manipulation of evanescent electromagnetic fields has been a key motivation in the field of plasmonics. However, one class of evanescent field has been excluded from consideration here - the evanescent field of moving free electrons. The electromagnetic energy of free electrons exists in the form of evanescent waves and it can be out-coupled to light only when the electrons are in close proximity to a 'slow-wave medium' or optical inhomogeneity. The former causes the well-known phenomenon of Cerenkov radiation, the latter diffraction or Smith-Purcell radiation. Here, in analogy to the 'poor-man's superlens', wherein the evanescent component of light from an object is restored by a thin silver layer to beat the diffraction limit, we demonstrate

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