金屬光子晶體應用於兆赫輻射控制之研究

Abstract

由於金屬在兆赫波段 (1012 赫茲) 具有極小而可忽略的吸收，利用金屬來製作適用於兆赫波段的光子晶體結構是一個相當好的選擇。此種結構是利用低成本並容易取得的不□鋼材料(SUS-304)，經由雷射加工的方式來產生具三角形排列之週期性圓孔的金屬光子晶體。利用兆赫時域光譜技術來量測樣品的穿透光譜，當兆赫波正向入射晶體時，我們發現禁止能帶和允許能帶的出現，此即為預期中的光子晶體現象，我們也報導利用相同結構的鋁合金光子晶體結果，他們的光譜特性與理論預期結果相符。然而對於不同的偏振態入射並不影響穿透光譜，即穿透光譜與偏振態無關，此亦為預期中的現象。另外近年來由於在表面電漿造成異常穿透提升的研究蓬勃發展，我們藉由在晶體表面貼上薄膜膠帶的方式來探討金屬光子晶體的兩側介質對穿透異常提升的影響。最後我們利用兩片晶體製作成具有特定間距的共振腔，發現會使得穿透峰更顯得陡峭，此可歸類於法布禮-派羅效應的影響。

Owing to negligible loss of metals in THz region, metals are good candidates for photonic crystals. Metallic photonic crystals with a periodical triangular array of circular holes were fabricated in THz region. The structures were made of low-cost, easily available stainless steels (SUS-304), and an array of holes was drilled by laser cutting. Using THz time-domain spectroscopy to obtain transmission spectra, phenomena of allowed and forbidden bands similar to photonic band gaps appeared when waves were normally incident, and the band can be well defined by Chen’s theory. This was also observed using the same structure of aluminum alloy crystals. The same spectra with varying polarizations of a normal incident THz wave ware found. It showed polarization independence. Then extraordinary transmission due to surface plasma effects by attaching tapes to crystals was explored. Finally, a Fabry-Perot etalon of two crystals with specific spacing was made. The sharper transmission peak caused by etalon effects was observed.