本論文中，討論了高尖峰功率下雙光子吸收對於兆赫波之產生的特性與影響。首先我們介紹輻射原理Drude-Lorentz 模型，並引入了低溫砷化鎵(LT-GaAs)的載子模型，分別模擬出單光子與雙光子個別對兆赫波所產生的影響。在理論的部分由模擬結果可知，隨著激發的光強度提升，單光子吸收所產生的兆赫波將達到飽和，而雙光子吸收則沒有飽和限制。此外，由於雙光子吸收與高尖峰功率有關，因此我們也探討了在不同脈寬與不同散焦(相同脈寬不同尖峰功率)下雙光子吸收與單光子吸收的差異。在實驗的部分，我們成功的利用8fs雷射激發光導天線，觀察到了光致電流非線性增加，突破原有80fs雷射的飽和限制。更藉由室溫偵測器(Golay cell)直接量測光導天線所輻射的兆赫波強度，定量的說明了雙光子吸收效應對於兆赫波的影響。
最後我們利用自行架設之兆赫波干涉儀，量測兆赫波強度的干涉行為，因其經傅氏轉換後在數學上可表示為兆赫波的頻譜振幅，可藉以量測單光子與雙光子的頻譜差異。

In this thesis, the characterization of the Two-photon absorption (TPA) induced extra photocurrent for Terahertz (THz) radiation under high peak power is studied. First of all, through combining the Drude-Lorentz model and the Low Temperature GaAs (LT-GaAs) carrier model, we simulate the influence of the THz under One-photon absorption (SPA) and TPA respectively. The theoretical simulation shows that: As the input power increase, the THz radiation generated by SPA will behave with nature of saturation. However, the generated THz radiation will keep increasing without saturation when the TPA has been taken into account. By adjusting the spot size with defocusing the excitation, we also investigate the photocurrent under various peak intensities. The result further confirms the nature of the nonlinear increase come form TPA rather than SPA
In addition, we experimentally observed the properties of photocurrent increase nonlinearly as the THz photoconductive antenna is excited by 8fs laser pulses. To quantative investigate the THz radiation, the Golay-Cell photodetector is used to measure the THz power. Finally, to characterize the broadband THz, a home-made THz interferometer is also demonstrated. Using the interometer, we compare and discuss the difference between role of SPA and TPA for THz radiation at frequency domain, respectively.

第一章、 緒論．．．．．．．．．．．．．．．．．．．．．．．．．．．．． 1
第二章、 兆赫波產生與偵測系統．．．．．．．．．．．．．．．．．．．．． 3
2.1 光導天線基本原理．．．．．．．．．．．．．．．．．．．．．．． 3
2.1.1 光導天線(Photo Conductor Antenna-P.C.A) ．．．．．．．．．．． 3
2.1.2 輻射原理Drude-Lorentz 模型．．．．．．．．．．．．．．．．．． 4
2.2 兆赫輻射偵測原理．．．．．．．．．．．．．．．．．．．．．．．14
2.2.1 偵測使用光導天線．．．．．．．．．．．．．．．．．．．．．．．14
2.2.2. 自由空間電光取樣法(EO sampling) ．．．．．．．．．．．．．．．16
2.3 結論．．．．．．．．．．．．．．．．．．．．．．．．．．．．．18
第三章、 高尖峰功率下雙光子吸收效應．．．．．．．．．．．．．．．．．．19
3.1 光導材料．．．．．．．．．．．．．．．．．．．．．．．．．．．19
3.1.1 砷離子佈植砷化鎵．．．．．．．．．．．．．．．．．．．．．．．19
3.1.2 低溫砷化鎵．．．．．．．．．．．．．．．．．．．．．．．．．．20
3.1.3 飽和問題．．．．．．．．．．．．．．．．．．．．．．．．．．．20
3.2.1 雙光子吸收對於載子產生率之影響．．．．．．．．．．．．．．．．24
3.2.2 雙光子吸收對於光致電流與兆赫波之影響．．．．．．．．．．．．．26
3.2.3 相同脈寬不同散焦下雙光子吸收對光致電流影響．．．．．．．．．．29
3.3.1 高尖峰功率下雙光子吸收效應．．．．．．．．．．．．．．．．．．31
3.3.2 高尖峰功率下雙光子吸收對於兆赫波幅射之影響．．．．．．．．．．32
3.3.3 不同雙光子吸收係數下對於兆赫波之影響．．．．．．．．．．．．．35
3.4.1 討論結構因子之屏蔽效應．．．．．．．．．．．．．．．．．．．．36
3.4.2 屏蔽效應下對於雙光子吸收對於兆赫波之影響．．．．．．．．．．．39
3.5 結論．．．．．．．．．．．．．．．．．．．．．．．．．．．．．42

第四章 實驗與分析．．．．．．．．．．．．．．．．．．．．．．．．．．．43
4.1.1 不同偏極角度下雙光子吸收特性．．．．．．．．．．．．．．．．．44
4.1.2 系統架構．．．．．．．．．．．．．．．．．． ．．．．．．．． 44
4.1.3 實驗結果．．．．．．．．．．．．．．．．．． ．．．．．．．． 45
4.2 不同散焦距離下的光致電流．．．．．．．．．．．．．．．．．．．46
4.3 不同脈寬下的光致電流．．．．．．．．．．．．．．．．．．．．．48
4.4 不同散焦與不同外加偏壓下之兆赫波特性．．．．．．．．．．．．．51
4.4.1 室溫偵測器．．．．．．．．．．．．．．．．． ．．．．．．．． 51
4.4.2 系統架構．．．．．．．．．．．．．．．．． ．．．．．．．．． 52
4.4.3 相同功率相同光斑大小、脈寬不同的下之兆赫波．． ．．．．．．． 53
4.4.4 不同散焦距離不同外加偏壓下的兆赫波強度．．．．．．．．．．．．56
4.6 結論．．．．．．．．．．．．．．．．．．．．．．．．．．．．．57
第五章、單雙光子頻譜特性．．．．．．．．．．．．．．．．．．．．．．． 59
5.1.1 單雙光子頻譜特性．．．．．．．．．．．．．．．．．．．．．．．59
5.1.2 不同脈寬下單雙光子頻譜模擬．．．．．．．．．．．．．．．．．．59
5.1.3 屏蔽效應下單雙光子頻譜分析．．．．．．．．．．．．．．．．．．63
5.2 兆赫波干涉系統．．．．．．．．．．．．．．．．．．．．．．．．66
5.2.1 兆赫波干涉系統架構．．．．．．．．．．．．．．．．．．．．．．66
5.2.2 干涉數學行為與模擬結果．．．．．．．．．．．．．．．．．．．．67
5.3 干涉實驗結果．．．．．．．．．．．．．．．．．．．．．．．．．69
5.4 結論．．．．．．．．．．．．．．．．．．．．．．．．．．．．．71
第六章、結論與未來展望．．．．．．．．．．．．．．．．．．．．．．．． 72
6.1 結論．．．．．．．．．．．．．．．．．．．．．．．．．．．．．72
6.2 未來展望．．．．．．．．．．．．．．．．．．．．．．．．．．．73
參考文獻．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．． 74
Publication List．．．．．．．．．．．．．．．．．．．．．．．．．．． 77

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