近年來奈米金屬結構與電磁波之間的相互作用所產生的表面電漿子(surface plasmon)已受到光學領域上學者高度的關注，因為其光場可以產生強近場並突破繞射極限(diffraction limit)，此重大發現對於次波長元件的應用相當有發展性。在奈米尺度下的透鏡也是利用金屬與介電質之間所產生的表面電漿子效應，進而強化奈米透鏡的聚焦效果並提高黃光微影曝光的解析度，讓半導體晶片的製程能夠進一步突破更微小的奈米等級。
本研究主要利用電子束蒸鍍機(E-beam Evaporator)將玻璃基板上面鍍上一層銀薄膜，再使用雙束型聚焦離子束(Dual Beam-Focused Ion Beam)在銀薄膜上蝕刻出一個同時具有凹槽與狹縫之同心圓結構。通過改變凹槽位置，我們研究了由此結構發出光束的聚焦特性。此外也使用了532nm和405nm兩種不同波長的雷射光去觀察當不同波長之雷射光打到金屬奈米結構所產生不同的表面電漿傳播效應。研究發現當調整凹槽在一個適當的位置時，金屬奈米狹縫結構發出405nm的光會產生一個長焦深和次波長尺寸的光點，532nm波長的雷射光也會隨著凹槽位置變化產生不同的發射光束。此外，銀金屬對於405nm雷射光與532nm雷射光有不同的吸收率，造成不同雷射光分別擁有了各自在銀金屬表面上的傳播長度。
為了驗證實驗的準確性，我們也使用了有限時域差分法(Finite Difference Time Domain)驗證實驗結果。最後模擬結果與實驗結果也非常的吻合。

The circular slit surrounded by surface groove (CSSG) structure can provide a long depth of focus (DOF) with different shapes of focusing spots for the different wavelengths of inci-dent light by modulating the locations of circular grooves. Furthermore, the mean radius of the circular groove can modulate the focusing properties of transmitted light from the CSSG structure. The focusing properties of transmitted light for 405 nm wavelength can be en-hanced to possess a long DOF and higher intensity by the circular groove on a proper loca-tion. It can be applied to micro-machining and photolithography because the transmitted light of the CSSG structure can provide a long working distance to eliminate other variations (such as vibration) during the fabrication process. The transmitted light of CSSG structure for 532 nm wavelength is expected to be a doughnut shape with a long propagation distance. The doughnut shape of the beam with a long propagation distance can be a versatile tech-nique for optical trapping by its radiation force.

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