電子束在經過週期性光柵結構時，會發射輻射，而此輻射我們稱之為Smith-Purcell radiation(SPR)，此輻射據有利用調控光柵週期來改變各個波段的輻射角度的特性， 若再透過Surface Plasmon(SP)效應來增強特定輻射的波段，來達成鎖頻的效果，即可產生一據有指向性的單頻輻射波。
此次研究目的在於透過SP-locked SPR的特性，與有限時域差分法軟體Lumerical來模擬與驗證，產生單頻匯聚光點(convergent beam)，透過PEC光柵週期與IMI基板的設計來達成，當電子束從材料底下經過時，各組光柵會發射出相同波長但不同角度的輻射光，且每束輻射光皆會往匯聚光點的位置發射，並以此設計為基礎，加以設計出多色匯聚光點(multi-color convergent beam)的成果，其是透過RGB三個區域拼接而成，每個區域發射的輻射波長與方向皆不同，最後我們還發現了，在單頻匯聚光點的結構下，將電子束的行進方向逆向，可以由原本的匯聚光點結果切換為發散輻射(divergent radiation)的結果
本次研究在於提供一個方法來設計一個可產生匯聚光點的光學元件，且在未來可以運用在許多光學領域中。

In this work, the generation of a convergent beam via using the SP-locked SPR is proposed by an insulator-metal-insulator (IMI) substrate with chirped gratings on the substrate. The chirped gratings are designed such that a convergent beam containing a single wavelength is formed directly above the gratings when an electron bunch passes beneath the substrate. The wavelength of the convergent beam changes with the refractive index of dielectric layer of the IMI structure, which is determined by the frequency of SP on the IMI substrate excited by the electron bunch.
Moreover, reversing the direction of electron bunch will make the emitted light from the proposed structure to switch from a convergent beam to a divergent beam. Finally, the formation of a convergent beam containing red, green and blue lights just above the chirped gratings is also demonstrated.

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