Plasmonic amplification of free-electron evanescent fields

So, J.-K., Ou, J.Y., Adamo, G., García de Abajo, F.J., MacDonald, K.F. and Zheludev, N.I. (2013) Plasmonic amplification of free-electron evanescent fields. Institute of Physics Singapore (IPS) Meeting '13, Singapore. 04 - 06 Mar 2013.

Abstract

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.

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 the use of an intermediate silver layer to amplify the free-electron evanescent field before it is out-coupled into light by a nano-grating. The presence of a silver layer provides for the excitation of phase-velocity matched surface plasmons, and leads to the amplification of the electrons' evanescent field.

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Contributors

Author: J.Y. Ou

Author: K.F. MacDonald

Author: N.I. Zheludev

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