現在關於THz的研究與應用由於其重要性越來越被人所關注，關於THz提高光強度及頻率窄化的要求也越來越重要。傳統的THz光參量振盪器均爲建立signal波的振盪，從而達到窄頻的效果。由於光參量產生器的過程中會產生signal及idle波，所欲我們從單純的signal波振盪拓展到THz波的振盪。衆所周知，一般情況下THz的波長在30 μm到3000 μm之間。我們選擇非線性晶體LiNbO_3作爲實驗材料，其原因一是因爲其非線性係數較大，二是其作爲常用非線性晶體方便易得。在THz光參量產生器中，THz的波長爲100μm到300μm。並且根據非線性過程中的相位匹配原理，THz波與泵浦光存在一個65度的夾角。通常狀態下，這種偏移會對實驗造成不好的影響，但是我們把這種情況與光柵進行了組合，從而產生了在y表面進行光柵反射的分佈式回饋光參量振盪器。通過鐳射或是切割的機械式方式在晶體表面製作光柵。並且根據穿透式光柵的特性，可以在與晶體表面垂直的方向上量測到THz的信號。根據光柵原理，通過在不同角度量測THz的能量大小，可以確定其對應的THz波長及大小，THz其波長半高寬在18μm,換算成頻率爲0.19THz。泵浦光中心波長爲1064.36nm。signal光中心波長爲1071.21nm,其波長半高寬爲0.6nm。

Nowadays the research and application of THz are more and more popular. The THz source of narrow band and high power output are becoming more and more important. The traditional method of getting a narrow band THz wave by optical parametric generation is to establish an optical parametric oscillation for signal. In this thesis, we expanded the THz parametric oscillation from the signal wave to the THz wave. As it is known, the wavelengths of THz wave range from 30μm to 3000μm. We chose the nonlinear crystal to do the experiment because of its high nonlinear coefficient and easy accessibility. In the THz parametric generation field, the wavelengths of THz range from 100μm to 300μm. Additionally, according to the phase matching condition for the nonlinear optics process, there is a 65 degree angle between the THz wave and pump light. In general, this walk-off effect is bad for the THz research; however we combine this effect with the grating effect to establish a y-surface reflection distributed feed-back THz parametric oscillation crystal. The grating is fabricated on the surface by the mechanical method of laser cutting. According to the transmittance effect of grating, we measured the THz wave in the vertical direction to the surface grating, which verifies our design. The narrow band THz can be measured by detecting the THz power in different angles because of the transmittance grating effect. The THz bandwidth is about 18 μm in wavelength or 0.19 THz in frequency. Correspondingly, the pump wavelength is 1064.36 nm and the signal wavelength is 1071.21 nm with a 0.6-nm FWHM bandwidth.

Abstract II
摘要 IV
Chapter 1 Introduction 1
A. Motivation 1
B. THz Source 4
C. THz Parametric Generation 5
D. Improvement of THz Performance 8
Reference 10
Chapter 2 Theoretical Analysis 12
A. Nonlinear Process in Noncentrosymmetric Material 12
B. THz Parametric Generation 16
C. THz Output Coupler 24
D. Waveguide Theory 29
E. Distributed Feedback 33
F. THz Parametric Oscillation 38
Reference 42
Chapter 3 Grating Design and Fabrication 45
A. Methods of Fabrication 45
B. Design 51
C. Measurement 54
Reference 57
Chapter 4 Experimental Result and Analysis 58
A. Experiment Setup 58
B. Result Analysis 60
Chapter 5 Conclusion and Future Work 67
A. Conclusion 67
B. Future Work 68

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