本論文利用Z-scan technique技術研究摻雜金奈米粒子配向膜的液晶之非線性光學特性。Z-scan technique光路架設簡易且對於物質非線性折射係數(光學柯爾係數n2)的量測具高靈敏度，其原理是基於樣品折射率隨光強度變化產生的光自聚焦或自發散效應，會使遠場產生改變，反推而得其相位及折射率的變化。
我們利用Z-scan technique觀察到，於配向膜掺雜金奈米粒子會大大增加液晶盒的光學柯爾係數，其原因是由於金奈米粒子透過表面電漿共振吸收入射光能量後所產生的熱效應，進而產生自發散效應。我們亦觀察不同的金奈米粒子掺雜濃度與不同的配向膜塗佈次數對液晶盒之非線性係數的影響，實驗成果得到最大的光學柯爾係數可達-4.29×10-4（cm2/W）。不同的入射光偏振分向與不同的環境溫度亦會對n2有所影響。實驗結果顯示在25~40℃間，平行液晶導軸方向的入射光使液晶盒產生自發散效應(n2＜0)，垂直液晶導軸方向的入射光使液晶盒產生自聚焦效應(n2＞0)，且於40℃時各自量測最大的光學柯爾係數。其結果可由液晶之非尋常光與尋常光折射率對溫度的關係圖來解釋。
此外，外加電壓的效應亦被探討，發現隨著電壓的增加，液晶盒 ｜n2｜值會先增大至一最大值，之後再慢慢遞減。且入射光強度越大，最大數值n2所需的電壓越小。這是由於光強度越高，溫度越高，克服Freederickz Transition所需的電壓較低，液晶較易被拉向電場方向。

This thesis studies the nonlinear properties of liquid crystals (LCs) with the cell substrates being treated with Au-nanoparticle-doped alignment films using the Z-scan technique, which is a simple but powerful technique to measure the optical Kerr constant of materials. The measurement is based on the spatial beam distortion observed in the far field as the laser baem is focused by lens and then pass through the nonlinearly sample which is z-scanned around the focus point.
Firstly, the use of Au-nanoparticle-doped alignment films in a LC cell to enhance the optical Kerr constant (n2) of LCs due to the thermal effect is demonstrated. The thermal effect is due to the light absorption induced by the localized surface plasmon resonance (LSPR) of the Au-nanoparticles, and induces self-defocusing effect of the sample. Besides, the results show that n2 can be further enhanced by increasing Au-nanoparticle concentration in the alignment film, or the spin coating times. It is found that the maximum n2, which is -4.29×10-4(cm2/W) can be obtained with the uses of optimum parameters.
Polarization and temperature effects are also studied. The optical nonlinearality of the sample with the LC director parallel and perpendicular to the beam polarization is self-defocusing and self-focusing effect, respectively, at temperatures below the clear point. The maximum ｜n2 ｜value is observed at 40℃ for both cases. The results can be properly explained by the use of the temperature-dependent refractive index traces of extra-ordinary and ordinary light. In addition, the nonlinear effect of the sample with an application of an AC voltage (1000 Hz, 0~30 Vp-p) is investigated。It is found that｜n2｜ increases to a maximum value initially, and then decreases with the applied voltage. Also, the higher input intensity requires the lower voltage to observe the maximum value. The phenomenon is due to the fact that the threshold voltage decreases with temperature.

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