電子束通過光柵會激發三種電磁波輻射，Smith-Purcell輻射、Mimic-SPP輻射以及Original-SPP輻射，其中Smith-Purcell輻射可做Millimeter Wave的輻射源，可應用領域非常廣泛，如軍事用途、生物醫療、民間產業，尤其是應用在生物醫療上，更是最近重要的話題，所以本篇論文著重在Smith-Purcell輻射的介紹。然而Smith-Purcell輻射要能實際應用的輻射源皆需大功率和性能良好，而高功率Smith-Purcell輻射目前還有待開發，這是目前Smith-Purcell輻射發展遇到的瓶頸。
本論文探討利用數值模擬方式研究當光柵表面鍍上Ag薄膜、改變薄膜厚度或是薄膜長度改變時的Smith-Purcell輻射的特性，試圖從中找尋可能增強Smith-Purcell輻射的方法。

The Smith-Purcell Radiation (SPR) is investigated using a two dimensional finite-difference-time-domain (FDTD) method. The permittivity of metal was represented using the Drude model. During the simulation, we observed three kinds of EM radiations when an electron beam passing over a diffraction grating. We think three kinds of EM radiation were basic SPR, mimic-SPP, and original surface plasmon polariton (SPP), caused by the periodic grating structure. In this paper, we also show surface plasmon polaritons can be enhanced SPR, in order to study the enhancement of Smith-Purcell Radiation, we use two models, model 1 is a perfect conducting grating (PEC) and model 2 is an Ag layer on the perfect conducting grating, in the simulation, we can find that by covering Ag layer on the perfect conducting grating, the amplitude of the electric field is enhanced two times than that only for perfect conducting grating. In the end of the article, we observed property of SPR which different of film length and thickness.

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