Amplification of the Evanescent Field of Free Electrons

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• 作者：Jin-Kyu So ; F. Javier Garc铆a de Abajo ; Kevin F. MacDonald ; Nikolay I. Zheludev
• 刊名：ACS Photonics
• 出版年：2015
• 出版时间：September 16, 2015
• 年：2015
• 卷：2
• 期：9
• 页码：1236-1240
• 全文大小：433K
• ISSN：2330-4022

文摘

Evanescent optical fields existing in close proximity to illuminated objects 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 鈭?50 THz (鈭?50 nm) spectral range for medium-energy (40鈥?0 keV) electrons.