| 摘要: | 本論文所使用之偶氮苯材料照射紫光可使其從反式轉變為順式結構；而照射可見光可從順式轉變回反式，此反應稱為光致異構化反應，且此反應為可逆反應，亦即可多次來回變換。偶氮苯材料之順式及反式結構通常具有不同的物理特性，因此廣泛應用於光控元件的製作。
本論文使用負型向列型液晶(HNG30400-200)、右旋手性分子(R1011)及左旋偶氮苯手性分子(ChAD-2-S)，並利用偶氮苯手性分子在反式結構與順式結構時之螺旋扭轉力差異，使膽固醇液晶反射頻譜隨照光波長及強度的不同而改變。本研究主要分為三部分，第一部分利用綠光及紫光同時照射該偶氮苯膽固醇液晶，在綠光強度固定的情況下，隨紫光強度增加，偶氮苯膽固醇液晶的反射頻譜往短波長藍移，可調整兩道光之強度以調控膽固醇液晶之反射頻譜，並觀察到當兩道入射光於適當強度範圍內皆增加時，其反射頻寬亦隨強度拓寬。此外，研究兩道入射光於液晶盒同面及反面入射時其頻譜變化之差異。第二部分利用光罩覆蓋該偶氮苯膽固醇液晶盒，在光罩側使用紫光照射，比較無光罩側有無使用綠光照射之膽固醇液晶盒反射頻譜之差異，並利用雙光同時照射製作二元膽固醇液晶盒，在空間上達成頻譜拓寬效果。第三部分將膽固醇液晶盒透過部分照光方式製作兩不同區域，分別反射短波長光及長波長光，利用反射鏡使寬頻光線來回經過膽固醇液晶盒不同區域各兩次，使反射頻譜相鄰區域之波長的光線能保留，使光線處理後留下窄頻寬成分。
;The trans-cis (cis-trans) transitions of azobenzene materials adopted in this thesis occur when they are illuminated with an ultraviolet (visible) light. Such a reversible reaction is called the photoisomerization effect. The physical properties of trans-isomers are usually different from those of cis-isomers, so azobenzenes can be widely applied to the applications of photosensitive optical devices.
In this thesis, the mixture of nematic liquid crystals (LCs) with negative dielectric anisotropy (HNG30400-200), right-handed chiral dopant (R1011), and left-handed chiral azobenzene (ChAD-2-S) was adopted. The disparities of the adopted chiral azobenzenes between trans-isomers and cis-isomers, such as the tunable helical twisting power (HTP), play the key to shift the reflection band of the cholesteric LCs (CLCs) with the illumination of different wavelength light sources. The topics in the thesis include three parts. The first one is to study the tunable reflection bands of the CLCs by simultaneously illuminating with green and purple light onto the CLCs. With the illumination of green light having a constant intensity, the CLC reflection band will be blue-shifted. The range of shifted wavelength increases with the increase of the intensity of purple light within a specific range. We also observed that the reflection band can be broadened by proper increasing the intensities of both lights. Additionally, the shifts of the reflection bands, resulting from the simultaneous illumination of green and purple lights from the same side and the opposite sides of the CLC cell were investigated. Second, binary planar textures with two different pitch lengths, generated by illumination of light through a suitable mask, in a single CLC cell are also proposed to spatially broaden the reflection band of the CLCs. The difference between the reflection band, resulting from the illumination of a single purple light, and that obtained by the simultaneous illumination of purple and green lights, was examined. As described in the first part, the simultaneous illumination of green and purple lights from the same side and the opposite sides of the CLC cell is worth to be discussed. In the last part, the approach to obtain a light source having a narrow bandwidth was proposed. With the illumination of purple light onto the part of the CLC cell, two regions, reflecting lights with different wavelength ranges, can be obtained. A wide-band light source becomes a narrow-band one if the incident light passes through the two regions in the CLC cell twice. As a result, the undesirable component of light can be filtered out, and a narrow band unpolarized light source can be retained. |
