Terahertz Smith-Purcell Radiation from Surface Plasmon Wave in One-Dimensional Photonic Crystal Structure using Counter-Streaming Electron Beam

A new THz Smith-Purcell radiation (SPR) free electron laser (FEL) using counter-streaming electron beams (CSEBs) on a one-dimensionally structured metal slab is introduced. The analytical dispersion curve and the calculated SPR-intensity of the CSEBs-SPR system explain how plasmon-transmissions between the CSEBs lower the tansition-threshold from a spontaneous emission to a stimulated one as well as enhance the radiation intensity. The self-frequency-locking effect of the system is verified by numerical simulations based on particle-in-cell (PIC) computation. On summary of the numerical analyses, the transition-threshold of CSEBs-SPR is lowered down to 2-3% of a conventional SPR. The radiation intensity of the former is about two orders of magnitude larger than that of the latter at the same beam-current density