Bimodal Spoof Surface Plasmons Excitation on a Depth-Modulated Composite Grating by Electron Beam

Spoof surface plasmon modes (SSPs) on the corrugated metallic surfaces are promising to develop a series of novel functional devices and systems in both microwave and Terahertz (THz) band. Due to its strong near-field localization and the versatile dispersion control, SSP mode excitations by injected energy beams (lasers or electron beam) are intensively studied in recent years. However, previous studies and demonstrations are mostly limited to single band high-efficient excitation on the single metallic grating. In this work, a bimodal SSP mode excitation on a periodical rectangular metallic groove depth-modulated grating with a closed metal plate by the same injected electron beam is proposed and studied by using particle-in-cell simulations. The dual-model SSP mode waveguide propagation is caused by integrating two kinds of uniform metallic grating with different groove depth, which can be excited and sustained by the same injected electron beam on two distinct frequency band independently. In order to verify the mentioned concept, a bimodal SSP mode excitation by using the high-energy electron beam is modeled and implemented in THz frequency. Besides, the excited strong electric field output spectrums in high frequency of
$\mathrm{f}_{1}=0.96\text{THz}$
and low frequency band of
$\mathrm{f}_{2}=0.77\text{THz}$
are presented and analyzed. The topic and studies are beneficial to the development of SSP-based dual-band or multi-band high-power radiation source in THz spectrums.