Investigation of terahertz coherent Smith-Purcell radiation in three-section periodical grating

In this paper, a three-section periodical grating structure (PGS) is investigated for Smith-Purcell (SP) backward wave oscillator (BWO). The first and second sections are used to pre-modulate the electron beam and the open grating (section-III) is for terahertz SP radiation. By theoretical analysis and particle-in-cell simulations, the SP radiation is studied in detail. The results show that the three-section PGS can drastically reduce the starting current of SP BWO, thereby generate the high frequency terahertz waves.