Enhancement of Coherent THz Smith-Purcell Radiation by Resonance Overlapping

Frequency-locked coherent Smith-Purcell Radiation (SPR) is emitted when a train of pre-bunched electron beam passes close to the surface of a metallic grating, which develops an energy density spectrum restricted to harmonics of the bunching frequency. For the lamellar grating with narrow grooves, the radiation spectrum from a single electron can also have a feature of narrow band, which is related to the grating structure and the beam energy. The combination of them is proposed in this paper. By properly choosing the parameters, the peak frequency of single electron radiation can be overlapped with the harmonics of the bunching frequency of the electron bunch train, leading to the generation of extremely intense narrow-band THz radiation.