Amplification of the Evanescent Field of Free Electrons
Jin-Kyu So, F. Javier García de Abajo, Kevin F. MacDonald, Nikolay I. Zheludev
1st January 0001
pp 1236 - 1240
electron beam, plasmonics, evanescent field amplification, Smith-Purcell emission, free-electron light sources
Evanescent optical fields existing in close proximity to illuminated bjects contain detailed information on length scales smaller than the wavelength. They do not propagate to external observers but can be
accessed using negative-index lenses, or coupled to propagating waves via subwavelength apertures, to achieve imaging resolution beyond the diffraction limit. Free electrons moving in vacuum also carry imperceptible localized, visible-frequency evanescent fields, and we demonstrate experimentally here that these fields can be amplified by a plasmonic film as electrons fly over the surface, offering new avenues toward the exploitation of electron evanescent fields for enhanced microscopy and nanoscale light generation. Amplifiers are fabricated at the tips of tapered optical fiber probes decorated with nanogratings to resonantly scatter electron fields to UV/vis light. We record amplification factors up to 3.4 in the ~850 THz (~350 nm) spectral range for medium-energy (40-50 keV) electrons.
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