半同軸狀金屬孔洞陣列於兆赫波之穿透特性

Abstract

在本論文中我們設計不同晶格常數、週期、厚度、以及單一晶格內兩個扇形金屬孔洞不同排列方式的半同軸狀次波長金屬孔洞陣列片，並且以兆赫波時域掃描系統量測其穿透率，以及使用時域有限差分法模擬分析其物理圖像，希望藉由實驗以及模擬來研究不同幾何結構參數對於異常光穿透率的影響。當改變晶格常數及週期時，我們發現異常穿透率現象發生在具有表面電漿耦合頻率大於或接近於單一金屬孔洞之截止頻率的樣品，並且其電場分佈主要集中在金屬孔洞之中；而當表面電漿耦合頻率小於單一金屬孔洞之截止頻率時，穿透率則會隨金屬孔洞的週期增加而快速下降，並且電場明顯地散佈在金屬表面上。當改變金屬片厚度時，我們發現金屬片厚度增加時穿透率峰值會隨之下降，但是峰值頻率並不會隨之變化。在改變單一晶格內兩個扇形金屬孔洞排列方式的實驗中，我們發現當兩個金屬孔洞之間進行水平方向的移動時，距離由最初的40微米移至300微米，其穿透率峰值頻率會往低頻的方向移動；而當我們將兩個金屬孔洞之間進行垂直方向的位移時，距離由0微米移至300微米，同樣也會發現穿透率峰值頻率會往低頻的方向移動。

In this thesis, we designed the semi-coaxial metal hole arrays with different lattice constant, period, film thickness, and the arrangement of two metallic sectorial holes to study the influence of these different geometrical parameters on the extraordinary optical transmission phenomenon. We measured these samples by terahertz time-domain spectroscopy (THz-TDS), and discussed the physical picture by using finite different time domain (FDTD) method. When we varied the lattice constant and period of semi-coaxial metal hole arrays, the extraordinary optical transmission is observed in those samples with the surface plasmon frequencies higher or closed to the cut-off frequency of metallic sectorial waveguide, and the electric field is distributed in the metallic hole. For the samples with the surface plasmon frequencies lower than the cut-off frequency of metallic sectorial waveguide, the transmission peaks are decayed rapidly as the period of hole arrays is increasing. As we varied the thickness of metallic film, we found the transmission peaks decayed as the film thickness is increasing, but the peak frequencies are unchanged. In the experiment of the variation of the arrangement of two metallic sectorial holes in a unit cell, we observed the peak frequency shifted to the lower frequency when the distance between two metallic sectorial holes of one unit cell shifted from 40 micrometer to 300 micrometer in the horizontal direction. Also in the vertical direction, the distance between two metallic sectorial holes of one unit cell shifted from 0 micrometer to 300 micrometer, we found the peak frequency shifted to the lower frequency.