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Abstract
Relativistic electron beams create optical radiation when interacting with tailored nanostructures. This phenomenon has been so far used to design grating-based and holographic electron-driven photon sources. It has been proposed recently that such sources can be used for hybrid electron- and light-based spectroscopy techniques. However, this demands the design of a thin-film source suitable for electron-microscopy applications. Here, we present a mesoscopic structure composed of an array of nanoscale holes in a gold film which is designed using transformation optics and delivers ultrashort chirped electromagnetic wave packets upon 30–200 keV electron irradiation. The femtosecond photon bunches result from coherent scattering of surface plasmon polaritons with hyperbolic dispersion. They decay by radiation in a broad spectral band which is focused into a 1.5 micrometer beam waist. The focusing ability and broadband nature of this photon source will initiate applications in ultrafast spectral interferometry techniques.
Highlights
Relativistic electron beams create optical radiation when interacting with tailored nanostructures
The lens operates by focusing the radiation as a result of the hyperbolic dispersion of the SPPs, which is due to the engineering of the spatial distribution of holes
An advantage of the electron-driven photon source (EDPHS) design in combination with spectral interferometry[35] is that the time between the electron excitation of the sample structure and the electron-generated optical probe is controlled on the attosecond scale
Summary
Relativistic electron beams create optical radiation when interacting with tailored nanostructures This phenomenon has been so far used to design grating-based and holographic electron-driven photon sources. Slower electrons interacting with optical and plasmonic gratings will emit coherent Smith–Purcell radiation which can interfere with the plasmon-induced radiation[28] Such a mechanism of radiation might be used to realize a miniaturized electron-driven photon source (EDPHS), though the large angular distribution of the emitted photons from the interaction of nonrelativistic electrons with nanostructures imposes the incorporation of feedback elements or closed waveguide geometries[29,30,31]. Holographic designs are perfectly suited for controlling the directionality of the emission[33] In this approach, the interference pattern of the electron-induced plasmons at the gold/air interface with a light field at a specific wavelength and with a desired shape is used to generate the required hologram; this method is highly frequency-selective. Our design principle facilitates the direct incorporation of the introduced EDPHS inside an electron microscope, to further pave the way for concomitant electron–photon spectroscopy and interferometry[35]
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