飛秒脈衝整型技術於兆赫波時析光譜儀之研究

Abstract

在本論文中，我們使用飛秒脈衝雷射整形技術研究鎖模雷射中之啾頻對於產生及偵測兆赫波輻射之影響。實驗結果發現，在兆赫輻射產生端，利用些微之正啁啾光來激發兆赫波光導天線會得到較強之兆赫波輸出，且具有較寬之頻譜。在偵測端，使用零色散之最短脈衝來偵測會得到最高之時域最大值，而且具有正負色散不對稱性之行為。我們使用一維Drude-Lorentz模型來模擬兆赫輻射的產生和偵測過程，藉此分析驗證我們的實驗結果。最後，我們使用此同調控制兆赫波時析光譜儀來研究若干樣本在兆赫波頻段之特性，如金屬孔洞陣列，乳糖及石英。我們並討論利用光導天線對進行兆赫波時析頻譜研究時可能會導致之偵測效應。實驗證明我們使用此同調控制之兆赫波時析光譜儀可以比一般的兆赫波時析光譜儀獲得較可信賴之光學常數。

In this thesis, we utilize femtosecond laser pulse shaping technology to study the role of chirp in generation and detection mechanism of Terahertz pulses with LT-GaAs photoconductive antenna. Experimental results show that the PC antenna excited with slightly up-chirped laser will generate THz pulses with higher peak amplitude, total power and broader bandwidth. In the detection process, similar behaviors have been observed. We use one dimensional Drude-Lorentz model to simulate THz generation and detection processes to analysis our experiment results. Finally, we use this coherently controlled THz-Time Domain Spectrometer to study the properties of several samples, such as fused silica, metal hole array and lactose. Experimental results show that we can utilize this spectrometer to get more reliable optical constants than the conventional approach.