Tuneable Terahertz Surface Plasmons Excitation in a Metal-Air-Metal Symmetrical Structure by Relativistic Electron Beam

One notable issue related to terahertz radiation generation is the tuneability of the source. In this manuscript, we study the properties of plasmons that arise when a beam passes through the gap between the plates. These metallic plates are separated by an air gap. A fast-moving electron beam can propagate in the gap between metallic plates without any divergence due to the minimum value of SPs electric field at the center of structure. As the electron beam is moving through the gap, it resonantly excites the SPs by the Cherenkov interaction between electron beam and SPs, at metal- air interfaces. These THz surface plasmons are transformed into THz radiation. The frequency of generated THz radiation can be tuned with varying the gap between the metallic plates and the electron beam energy. The proposed structure will open the possibility to design a compact source for coherent and tuneable THz radiation generation in broad spectrum regime, which will be useful for medical diagnostics, photonics devices, etc.