兆赫波是一介於高頻微波與遠紅外光之間的電磁波，其頻率一般定義在0.1兆赫到10兆赫之間。還擁有一些其它電磁頻段所沒有的特殊性質，例如:可用在危險氣體、藥品、毒品，甚至是爆裂物......等有機物的檢測應用上，所以近年來利用兆赫波的分子感測和影像技術激起廣泛的研究。本論文則設計和製作各種不同多層孔洞堆疊結構元件，與利用兆赫波反共振中空波導為基礎之內視鏡實現揮發性氣體感測。
我們使用親水性聚對苯二甲酸乙二酯( polyethylene terephthalate；PET)材料，多層堆疊具孔洞結構之PET薄膜，製作四種不同元件，用以感測揮發性氣體分子。根據兆赫波時域光譜儀所量測到的吸收率和等效折射率變化，來達到辨識不同種類、不同濃度、和相似氣體但依不同混合比例之揮發性氣體。本論文對不同元件結構進行氣體偵測之靈敏度探討。實驗結果顯示該親水性多層孔洞結構對丙酮具有特定辨識性(specific detection)，且最佳偵測靈敏度發生在具最小微孔洞之均勻多層堆疊結構，其最低可偵測的丙酮氣體莫耳密度為0.07 nano-mole/mm3，相當於4.12 ppm。該靈敏度可以應用到臨床醫學的辨識酮酸中毒，以及工業環境安全檢測。
另外，我們也利用以反共振中空波導為基礎之兆赫波內視鏡，成功辨識不同濃度之有機氣體分子。由於兆赫波在波導中的多重反射可以增加電磁波和待測樣品的作用長度，以及利用波導中之反共振模態，使得我們只要以一根30公分之玻璃管即可達到辨識微量揮發氣體。對於丙酮蒸氣，其最小可偵測的莫耳密度為0.07 nano-mole/mm3，相當於4.08 ppm；而對於氨氣，最小可偵測的莫耳密度為0.85 nano-mole/mm3，相當於29.95 ppm。並且在即時監控量測不同濃度之丙酮蒸氣實驗中，顯示該蒸氣偵測系統的反應時間介於300~800秒之間，並具有高度重複性。該系統對未來在臨床上人體之呼氣檢測、沼澤毒氣及危險氣體遙測具有相當的應用潛力。

Terahertz (THz) wave is located between microwave and visible light and with frequency ranging from 0.1 THz to 10 THz. Based on the spectral fingerprints in this frequency range, various dangerous materials, such as organic vapors, drugs, poisons and explosives, with similar appearances can be directly identified without labeling process. Recently, THz technology grows rapidly and various THz applications have been extensively developed, which are attributed to the great advances of THz generation and detection techniques, especially in THz molecular sensing and bio-imaging. In this thesis, we designed different multi-layer porous stacked structures, and utilized THz anti-resonant reflecting hollow-core waveguide based endoscope to realize volatile gas sensing.
We fabricated four kinds of multilayer-stacked porous structures using hydrophilic porous polyethylene terephthalate (PET) thin film for volatile gas sensing. Based on the variations of THz absorption coefficient and the effective refractive index measured by terahertz time-domain spectroscopy, we are able to successfully identify different kinds, concentrations and even different mixing ratio of volatile gases. In this thesis, we also explore the detection sensitivity under different geometric parameters of devices, such as thin-film-arrangement and pore size. The experimental results show that the demonstrated multilayer-stacked porous device enables to specific detection of acetone vapor, and the best detection sensitivity achieved 0.07 nano-mole/mm3, corresponding to 4.12 ppm. It occurs in the uniform-stacked porous device with pore size of 45μm. The results implies it is potentially applied to medical, industrial, and environmental gas detection.
In addition, we also used the terahertz endoscope based the anti-resonant reflecting hollow-core waveguide to successfully identify different kinds and concentrations of volatile gases. Because multiple reflections of terahertz wave in the waveguide can increase the interaction length between electromagnetic waves and analytes, and use evanescent wave of anti-resonant modes in the waveguide to detect, allow us can achieve recognition trace volatile gases by a 30cm-long glass pipe. For acetone vapor, the minimum detectable molecular density can be achieved 0.07 nano-mole/mm3, corresponding to 4.08 ppm; while for ammonia vapor, the minimum detectable molecular density can be achieved 0.85 nano-mole/mm3, corresponding to 29.95 ppm. And in the real-time monitoring and measurement of different concentrations of acetone vapor experiments showed that the vapor detection system response time is less than 300 seconds, and has a high degree of repeatability. The system for the future of the human body in clinical breath testing, toxic gas in the swamp and dangerous gas remote sensing has considerable potential applications.

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