Spoof surface plasmons (SSP) on the corrugated metal surfaces has attracted intense research interests and can find many interesting applications such as wave guiding, imaging, sensing, etc in microwave and terahertz (THz) band. Previous studies show that the intense near-field of SSP mode on the metallic grating can be used to develop a new enhanced radiation source which is induced by injected electron beam. In this paper, we study SSP mode on a modified metallic grating, i.e. the inverse L-shaped sub-wavelength metallic grooves. The general dispersion relation is obtained with a modal expansion method by solving field expressions in different regions along with proper boundary conditions. The theoretical result is also verified by finite integration method and good agreement is observed. Based on the dispersion result, a terahertz radiation source on the inverse L-shaped metallic grooves is proposed and studied by FDTD simulation. The results reveal that SSP mode can be efficiently excited by injected electron beam when the dispersion is matched well with each other. Also, the output power revolution of SSP mode and electron beam energy change are presented in the structure. The presented studies are instructive to design more efficient THz electronic sources based on the generation of SSP on the corrugated metal surface with gradient groove depth.
We investigate the ISAR imaging in background noises by using the analytical solutions and physical optics within the terahertz region. When increasing the frequency band wide, the scattering signals of the metal sphere are enhanced by the coherent measurement technique, and the background noises are effectively canceled. Furthermore, the resolution of SAR imaging is improved to precisely locate the scattering centers of objects. However, the increased band wide seemly decreases the contrast of imaging due to the discrete grids of filtered back projection algorithm.