本論文利用 Z-scan 技術研究摻雜偶氮染料之液晶薄膜之非線性特性，比較向
列型液晶與膽固醇液晶之非線性效應之特性差異，其目的是想得到一個與入射光
偏振無關之強非線性效應。Z-scan 技術的原理是由於樣品的非線性折射會產生自
聚焦或者自發散效應，利用其自聚焦或者是自發散的程度計算其相位，進而推估
折射率變化。此技術只需使用單一光束和簡單的實驗架設，就可以量測材料的非
線性吸收係數與非線性折射係數，是一個架設簡單觀察容易，量測物質非線性特
性強而又力的實驗架設。
在本論文的第一部分，我們使用 Z-scan 技術量測到偶氮染料掺雜液晶薄膜
(azo-dye-doped liquid crystal，ADDLC)之非線性效應。由於水平配向液晶薄膜
的雙折射性及染料分子長短軸之吸收率差異，當入射偏振光與液晶排列方向相同
時，具有比各向同性態時大之自發散現象。而入射光與液晶排列方向垂直時，則
是自聚焦效應，且 值比各向同性態小。由此可知，水平排列的 ADDLC 之非線性
效應具有很強的偏振相關性。
而在第二部分，為得到與偏振無關之液晶非線性特性，我們製作摻雜偶氮染
料的膽固醇液晶，讓液晶處於平面螺旋結構(planar texture)的排列，並讓膽固
醇液晶之反射波段避開入射光波長。我們研究了不同染料濃度引致的非線性效應
差異，並量測不同偏振入射光的影響，發現隨著染料濃度的增加 n2也會增加，且
不同偏振引致之非線性係數相同。此時入射光在液晶中的折射率為一平均折射率
效果。偶氮染料也因為主客效應呈現螺旋排列，不同偏振光對染料的吸光率一致。
由上述實驗結果，利用染料參雜之膽固醇液晶平面螺旋結構，我們可以得到
具有液晶之高非線性效應特性，同時排除液晶之高偏振相關性，成功得到一偏振
獨立且高非線性效應之光學材料。

In this thesis, the nonlinear properties of dye-doped liquid crystal films measured
via Z-scan technique are presented, and we’ve also compared the features of nonlinear
effect between nematic and cholesteric liquid crystals, because the purpose was to
obtain a strong nonlinear effect which is polarization independent. The nonlinear
refraction of the samples would induce self-focusing/self-defocusing effect, therefore
the Z-scan technique was utilized for the measurements in this study. The degrees of
self-focusing/self-defocusing effect can be used to calculate the optical Kerr constants n2
related to the variation of refractive indices. Moreover, this technique is
uncomplicated and powerful for nonlinear effect observations, because it only requires a
single laser beam and a simple setup to measure both nonlinear refractive indices and
nonlinear absorption coefficients.
In the first section of the study, we had investigated the nonlinear effect of
azo-dye-doped liquid crystal (ADDLC) films by Z-scan technique. Owing to the
birefringence provided by homogeneous-alignment liquid crystal films and the
absorption difference between the long axis and the short axis of the azo dye, the
self-defocusing effect in nematic phase was larger than that in isotropic state as the
polarization of incident light was parallel to the long axis of aligned liquid crystals.
While we set the incident polarization perpendicular to the long axis of liquid crystals, a
self-focusing effect was observed and the in nematic phase was found smaller than
that in isotropic state. As a result, it can be analyzed that the nonlinear effect of
homogeneous aligned ADDLC films is intensely polarization-dependent.
In the second section, in order to acquire a polarization-independent nonlinear
effect, we fabricated the azo-dye-doped cholesteric liquid crystal (ADDCLC) films
which were arranged in planar texture with the reflection bands managed to avoid the III
wavelength of incident light. We had studied the nonlinear effects in different
concentrations of the azo dye and also measured the influence of incident polarizations.
We discover that when the concentration of dyes was raised, the n2 increased as well;
the nonlinear indices were almost the same in various polarized light. The incident light
suffered an average refractive index in an ADDCLC film, and azo dye arranged in
helices resulted in identical absorption to different polarized light. In summary,
employing ADDCLCs with planar texture in nonlinear optical applications, we could
achieve not only strong nonlinear effects but also high polarization independence in
liquid crystals.

摘要 ................................................................................................................................................ I
Abstract ......................................................................................................................................... II
目錄 ............................................................................................................................................. IV
圖目錄 ......................................................................................................................................... VI
表目錄 ......................................................................................................................................... IX
第一章 液晶簡介 ..................................................................................................................... 1
1-1 前言 ............................................................................................................................. 1
1-2 何謂液晶 ..................................................................................................................... 1
1-3 液晶分類[2] ................................................................................................................. 2
1-3-1 棒狀分子之各相特性[2] ............................................................................................ 3
1-4 液晶的物理特性[3] ..................................................................................................... 6
第二章 理論 ........................................................................................................................... 13
2-1 光引致分子重新轉向效應 .............................................................................................. 13
2-1-1 正力矩效應-Janossy model[5-9].............................................................................. 13
2-1-2 負力矩效應-Gibbons model[10-12] ............................................................................ 15
2-1-3 光激發同素異構化反應[13-15] .............................................................................. 16
2-1-4 光致熱效應 .............................................................................................................. 17
2-2 Z-scan technique[3] .......................................................................................................... 17
2-2-1 三階非線性項的介紹 .............................................................................................. 18
2-2-2 Z-scan 架設下的非線性折射率 .............................................................................. 21
2-2-3 Z-scan 架設下的非線性吸收 ................................................................................... 24
2-2-4 Z-scan 理論[15] ........................................................................................................ 26
第三章 實驗樣品準備 ........................................................................................................... 30
3-1 實驗所用材料 ................................................................................................................. 30
3-1-1 向列型液晶-E7 ........................................................................................................ 30
3-1-2 偶氮染料-DR1 ......................................................................................................... 32
3-1-3 旋性物質-CB15........................................................................................................ 33
第四章 實驗光路架設與方法 ............................................................................................... 39
4-1 Z-scan 實驗光路架設 ....................................................................................................... 39
4-2 實驗流程與步驟 ............................................................................................................. 40
第五章 結果與討論 ............................................................................................................... 44
5-1 摻雜偶氮染料向列型液晶之Z-scan 量測 ..................................................................... 44
(1) 液晶導軸方向與偏振光平行 ................................................................................... 44
(2) 液晶導軸方向與偏振光垂直 ................................................................................... 47
5-2 摻雜偶氮染料膽固醇液晶之Z-scan 量測 ..................................................................... 49
(1) 不同溫度下的Z-scan 曲線 ....................................................................................... 50
(2) 不同角度的偏振光的Z-scan 曲線特性 ................................................................... 60
第六章 結論 ........................................................................................................................... 62
第七章 參考文獻 ................................................................................................................... 64

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