在液晶中許多的光非線性現象是源自於光與物質間的交互作用所引起。由於液晶擁有折射率隨溫度變化以及雙折射的性質，當光束進入液晶中，光場對液晶分子重新取向或光強造成液晶溫度改變皆會使光束感受到的折射率改變，因此雷射光在液晶中會產生一些有趣的光非線性現象。本論文主要研究液晶中光的非線性行為，以及利用蝕刻ITO玻璃控制電場分佈來探討光電領域上的應用。其中，主要分成三個實驗來討論及研究:
第一，利用外加電場輔助，在液晶中可以使用較低強度的光場對液晶分子重新取向，導致折射率的改變，產生自聚焦效應，當自聚焦效應平衡繞射效應，光束在液晶中會形成空間光孤子。另外，研究光孤子的交互作用，光孤子會建立一個折射係數的勢井，另一道光孤子會受到勢井的影響被吸引，若兩道光孤子之間的距離及角度適當，將會形成螺旋狀的形式向前傳播。
第二，實驗中蝕刻ITO玻璃形成光柵型電極分佈，在外加電場下重新排列液晶分子，使液晶分子形成週期性排列,研究光束在液晶中傳遞的情形。藉著conscopic實驗，觀察在不同電壓下，液晶折射率的變化情形，並且利用數學軟體模擬實驗結果，了解折射率的梯度變化。將光束打進液晶所形成的通道中，改變入射位置及角度，我們已經觀察到幾種現象，包括光孤子，波狀的光束，全反射和偶合的情形。
第三，我們將實驗溫度控制在臨界溫度附近，液晶折射率對溫度的變化會變得更明顯，並且在臨界溫度附近，雷射光較容易拉動液晶分子，我們改變不同的雷射光強度，可以觀察到不同光的非線性行為。接著，我們藉由conoscopy結合顯微鏡觀察液晶分子，這個技術提供一個方便的方法可以同時觀察光的非線性行為以及液晶分子受光場影響後的排列情形。

Many phenomena associated with nonlinear optics are produced by the light-matter interaction in liquid crystals. Nematic liquid crystals possess the properties of the birefringence and that refractive indexes of nematic liquid crystal vary with temperature. As a light beam propagates in liquid crystals, the light beam experiences changes of refractive indexes because the optical field reorientates molecules or the optical intensity changes the temperature of liquid crystal. Then, some interesting phenomena of optical nonlinearity produce in liquid crystals. This study investigates mainly the nonlinear behaviors in nematic liquid crystals. By etching ITO glasses to control distribution of electric field, we discuss applications in photo-electric field. These works are described as follows:
First, a low voltage was applied to a planar nematic liquid crystal cell; the director field can be reoriented using a low intensity. Then, the self-focusing effect produces due to a variation of refractive indexes. The light beam in nematic liquid crystal forms a spatial soliton by producing the effect of the self-focusing to balance the diffraction. Additionally, we study the interaction between solitons. One soliton creates a potential well of refractive index, anther one will be attracted in the potential well. As the separated distance between two solitons and the pumping angle are appropriate, two solitons propagate in the form of spiral.
Second, we study the behavior of light in a periodic refractive index medium. The director field of the nematic liquid crystal (NLC) is reorientated in a grating–like indium-tin-oxide electrode cell by applying a controllable-voltage. The variation of refractive index with voltage varied 0v to 10v was observed by a conoscopic method. Numerical simulations have reproduced the main features of the gradient distribution of refractive index in the waveguide. Several phenomena of a polarized laser beam that propagated in the waveguide with different incident angles and positions have observed by a CCD camera, including solitons, undulate beam, the total internal reflection and beam coupling.
Third, at the temperature close to nematic-isotropic phase transition temperature, the variation of refractive index in the liquid crystal becomes obvious to the change of temperature. And, a laser beam can easily reorientate molecules. We changed beam intensity in liquid crystal cell, different nonlinear phenomena were observed. Besides, A combined microscopic and conoscopic technique was used in experiments as a convenient way to analyze the optical nonlinearity that is associated with the molecular configuration of nematic liquid crystal.

第一章 緒論
1.1液晶簡介
1.1.1 液晶歷史……………………………………………………1
1.1.2 液晶種類……………………………………………………2
1.2光孤子簡介
1.2.1 孤粒子………………………………………………………5
1.2.2 空間光孤子…………………………………………………6
第二章 液晶物理
2.1秩序參數……………………………………………………………..8
2.2 連續彈性體理論…………………………………………………….9
2.3 液晶光電特性
2.3.1 液晶光學異向性……………………………………………11
2.3.2 電場對絕緣向列型液晶的影響……………………………15
2.3.3 Freederickzs轉變……………………………………………16
第三章 液晶的非線性光學特性
3.1 Optical Freedericks transition (OFT)……………………………..17
3.2 雷射光引致液晶分子重新取向…………………………………...21
3.2 液晶的熱效應
3.3.1 Thermally enhanced reorientational nonlinearity……………23
3.3.2 熱的非線性…………………………………………………24
第四章 外加輔助電場幫助雷射光引致液晶分子重新排列
4.1 前言…...……………………………………………………………27
4.2 實驗方法
4.2.1 樣品製作……………………………………………………29
4.2.2 聚光干涉實驗檢測樣品……………………………………32
4.2.3 實驗裝置……………………………………………………36
4.3實驗結果與討論
4.3.1 液晶中雷射光引致光孤子…………………………………37
4.3.2 液晶中光孤子的交互作用…………………………………44
參考文獻………………………………………………………………..48
第五章 雷射光在柵狀電極所形成液晶波導的傳播行為
5.1 前言……………………………………………………………...…50
5.2 實驗方法
5.2.1 樣品製作…………………………………………………....51
5.2.2 實驗裝置……………………………………………………54
5.3實驗結果與討論
5.3.1單條電極在液晶cell中形成的液晶波導………………….55
5.3.2二條電極在液晶cell中形成的液晶波導………………….71
5.3.3多條電極在液晶cell中形成的液晶波導………………….76
參考文獻………………………………………………………………..81
第六章 在臨界溫度(TNI)附近液晶cell中光的非線性現象
6.1 前言……………………………………………………………...…83
6.2 實驗方法
6.2.1 樣品製作……………………………………………………85
6.2.2 實驗裝置……………………………………………………86
6.3實驗結果與討論
6.3.1 雷射光在液晶中引致相位變化……………………………88
6.3.2 雷射光在臨界溫度(TNI)附近液晶cell中的傳播行為……95
參考文獻………………………………………………………………120
第七章 總結…………………………………………………………..121

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