Amplification of the evanescent field of free electrons

So, J.K., Ou, J-Y., Adamo, G., MacDonald, K.F., García de Abajo, F.J. and Zheludev, N.I. (2012) Amplification of the evanescent field of free electrons. SPIE Photonics Europe 2012, , Brussels, Belgium. 16 - 19 Apr 2012.

Abstract

We show that the conversion of the evanescent field of free electrons into optical radiation can be enhanced by amplifying the electrons' evanescent field. In the same way a layer of plasmonic metal can be used to amplify evanescent fields in the 'poor-man's superlens', it can be used to enhance Smith-Purcell radiation.

The electromagnetic energy of free electrons exists in the form of evanescent waves and can be decoupled into light only when they are in close proximity to a slow-wave medium or optical inhomogeneity. Since the exponentially decay rate of such evanescent waves is proportional to the ratio of the frequency of the electromagnetic field to the velocity of the particle, high velocity, relativistic particles are more efficient in generating light in the optical part of the electromagnetic spectrum. Here, instead of increasing the energy of the particles to gain a higher level of conversion, we utilize a thin silver layer to amplify the rapidly decaying evanescent waves of non-relativistic free electrons. A silver layer a few tens of nanometres thick placed between the free electrons and nano-grating provides an order of magnitude enhancement of Smith-Purcell radiation in the UV range.

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Contributors

Author: J-Y. Ou

Author: K.F. MacDonald

Author: N.I. Zheludev

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