當電子束通過週期性金屬光柵時，激發出Smith-Purcell輻射，此輻射可透過光柵週期來改變輻射角度。若再透過Surface Plasmon特性來提升特定輻射的波段，即可產生指向性的單頻輻射波。然而目前Smith-Purcell輻射只能產生沿電子束方向的輻射波，所以我們增加Yagi-Uda奈米天線陣列的機制來產生與電子束方向垂直輻射的特性並進行討論。
本研究利用FDTD Lumerical solution進行模擬，在Yagi-Uda奈米天線陣列上利用表面電漿操控Smith-Purcell輻射來產生匯聚光點的研究。我們分析三種不同類型的Yagi-Uda奈米天線的驅動器來產生匯聚光點，分別為在共振下長軸與偏振方向呈平行與垂直及在非共振下的條件，而我們發現到共振條件的奈米天線，其輻射角度為50度，而非共振條件為60度。另外，我們可以改變非共振條件的驅動器尺寸來改變遠場的輻射強度，並以此特性來設計出多個光點的結果，本研究可提供一個新方法在光學成像、全息術等領域中。

In this work, the generation of convergent light spot via using electron beam moving parallel to the Yagi-Uda nanoantenna arrays based on surface plasmon-manipulated Smith-Purcell radiation is proposed and investigated by FDTD simulation. We demonstrated three different types of Yagi-Uda nanoantenna’s feed to generate convergent light spot : the polarization which is parallel, vertical to the long axis of the feed under resonance and under non-resonance condition. In the case of resonance, the emission angle of the nanoantenna is 50 degree, while the non-resonance is 60 degree. Moreover, the size of the non-resonant feed can change the radiation intensity of the far field, so we can do more optical control on the optical element. This work offers potential applications in the fields of optical imaging, holography, etc.

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