當電子束通過期性金屬結構時會激發Smith-Purcell輻射(SPR)，而Smith-Purcell輻射的輻射波段與結構週期成正比，故我們可利用Smith-Purcell輻射可做為可見光、紅外光、兆赫波波段等輻射光源。但目前Smith-Purcell輻射遇到的最大瓶頸在於功率太小，所以我們需要找到能實際應用且提高功率的輻射機制 。
本篇論文利用有限時域差分法(FDTD)軟體Lumerical探討三種增強Smith-Purcell輻射的機制，分別為表面電漿效應(Surface plasmon polarition)、類表面電漿效應(Mimic surface plasmon)以及侷域性表面電漿效應(Localized surface plasmon)。我們將Smith-Purcell輻射波段鎖定於可見光波段，並且比較電子束通過光柵與週期性次波長表面結構(metasurface)時所激發Smith-Purcell輻射的差異，改變結構週期、大小、形狀、電子束速度等變因加以分析。

An electron beam passing over metallic gratings can generates Smith-Purcell radiation (SPR). The emission frequency and angle strongly depend on the period of gratings which can be designed. However, the electromagnetic wave radiated by SPR is non-directivity and has low radiated power. The FDTD method is used to simulate the process of radiation emission. In this work, we investigate three kinds of mechanisms of enhancement of SPR. One is enhanced by surface plasmon polarition (SPP) excitation, another is enhanced by mimic surface plasmon polarition (MSP) excitation, and the other is enhanced by localized surface plasmon (LSP). The third mechanism cannot use the grating to excite, so we change the grating to periodic metasurface. Furthermore, the enhanced emission frequency changes with the period, size and shape of the structure and the electron beam energy. The three kinds of mechanisms can be applied to realizing the compact and tunable visible light source.

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