Abstract
The coupling between surface plasmons and free electrons may be used to amplify waves or accelerate particles. Nonetheless, such an interaction is usually weak due to the small interaction length or velocity mismatching. Here a mechanism for enhancing the coupling between plasmonic fields and relativistic electrons is proposed. By using a weakly gradient meta-surface that supports the spoof surface-plasmons (SSP), the phase velocity of SSP mode can be manipulated and quasi-velocity-matching between SSP and electrons may be achieved. The dynamic coupling equations suggest that, due to the strong coupling, the energy can be extracted continuously from the relativistic electrons. The sustained increase of SSP in a narrow frequency band has been demonstrated by the particle-in-cell simulations, where the output power of SSP attains 65 W at 1 THz (with 28 mm interaction length) and the coupling efficiency is enhanced by two orders of magnitude. The results may find potential applications for designing new compact and efficient THz wave sources.
Highlights
The coupling between surface plasmons and free electrons may be used to amplify waves or accelerate particles
The electric-field force will change the velocity of electrons, especially in the strong coupling regime
Metasurface may refer to a special kind of quasi-two-dimensional film surfaces, which are structured artificially with periodic, quasiperiodic or aperiodic order, owning exotic optical properties in such as the refraction, absorption, phase, and polarization, etc
Summary
The coupling between surface plasmons and free electrons may be used to amplify waves or accelerate particles. Such an interaction is usually weak due to the small interaction length or velocity mismatching. It was shown that, when an electron beam passes through an unstructured metal film (or near a metallic nanostructure), the propagating SPP mode (or localized plasmon mode) can be excited[8,9] Based on this effect, a Cherenkov radiation source operating in the visible or ultraviolet frequency range was proposed[10]. The dynamic coupling equations indicate that, with the QVM design, the energy of relativistic electrons can be extracted continuously and efficiently in short interaction length. We present the www.nature.com/scientificreports particle-in-cell (PIC) simulations in the THz band, showing that the output power or coupling efficiency can be enhanced by two orders of magnitude
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