本論文研究光學差頻產生（DFG）和極化子散射（SPS）在5%摻雜濃度的 摻鎂鈮酸鋰（5% 〖MgO:LiNbO〗_3）中產生連續波（CW）之太赫茲 （THz）輻射的實驗。為了達到能激發上述兩種非線性光學的強度，設計成由雷射腔內的高強度共振光來產生太赫茲輻射。極化子散射太赫茲中之基本（fundamental）波和斯托克（Stokes）波分別是由使用 0.2% 和 0.25% 摻雜濃度的摻釹釩酸釔(〖Nd:YVO〗_4)作為雷射晶體的雷射腔生成，兩個雷射腔的雷射波長分別為1064.2 nm和1072.6 nm並且以一個相位匹配角對齊，兩個腔體產生了數瓦的腔內功率. 本論文的實驗緊湊地建構了一個斯托克雷射腔，而不僅僅是一個共振腔。高功率的斯托克波可以指數性地放大太赫茲輻射。透過焦電式光感測器和鎖相放大器的測量，測量之連續太赫茲波的輻射功率達到奈瓦（nW）等級。
本論文也呈現了設計這兩個高品質因子（Q-factor）之雷射腔的步驟，第一個是利用腔體震盪法（CRD）去測量三個超高反射率鏡子的反射率。第二個則是研究團隊設計的法布立－佩羅標準具（etalon），它的自由光譜範圍（FSR，40 nm）、透射率（約100%）和適當的半高全寬（FWHM，10.5 nm），在本論文中證明能夠從釹摻雜（Nd^(3+)）的雷射晶體選擇1064.2或1070.5 – 1073.4nm的共振波長。最後，經過電腦運算設計了抗反射次波長光柵（AR SWG）的耦合器，讓太赫茲從矽基板穿透至空氣中的穿透率達到近100%，而該次波長光柵僅需在矽基板加工出次波長大小的微結構，不需複雜、困難的光學鍍膜技術。

This study investigates the potential for continuous-wave (CW) terahertz (THz) radiation generation through optical difference-frequency generation (DFG) and stimulated polariton scattering (SPS) in 5% MgO-doped lithium niobate (LiNbO₃). An intracavity configuration is implemented to facilitate high-intensity laser-induced nonlinear optical (NLO) processes. Two Nd:YVO₄ laser crystals, doped at 0.2% and 0.25%, are placed in two separate laser cavities to generate the fundamental and Stokes waves, respectively. The resonant wavelengths in the two cavities are 1064.2 nm and 1072.6 nm. These cavities are precisely aligned according to the phase-matching angle for SPS in LiNbO₃. The dual lasers generate several watts of intracavity power, providing a strong pump and Stokes field, subsequently enabling THz-wave emission through DFG. The CW THz radiation power, on the nanowatt (nW) scale, is detected using a pyroelectric detector and lock-in amplifier.
To generate a strong intracavity power, this thesis constructs the two low-loss laser cavities. Various strategies have been developed to address this challenge. First, a cavity ring-down (CRD) experiment is used to measure the mirror reflectivity of supermirrors (R > 99.5%). Second, an intracavity etalon is incorporated to select the precise wavelength of the Stokes wave. A custom-designed etalon with a high free spectral range (FSR) of 40 nm, near 100% transmission peak, and a full width at half maximum (FWHM) of 10.5 nm successfully selects the resonant mode between 1064.2 nm and 1070.5–1073.4 nm in the Nd³⁺ gain crystal. Lastly, a computationally designed optical microstructure, specifically an anti-reflection (AR) sub-wavelength grating (SWG), enhances THz radiation coupling from a silicon substrate to air. The SWG achieves near 100% transmission with simple periodic grating fabrication, eliminating the need for complex optical coatings at THz wavelengths.

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