臺灣博碩士論文加值系統

摘要
本論文主要包含三個實驗。實驗I是聚合物 / 液晶混合材料添加少量主-客型染料分子做成全像光柵時，動態繞射效率變化的研究。在各種不同的液晶濃度和硬化強度下，量得的繞射曲線呈波浪起伏變化，有二至三個波峰產生。經由光散射實驗的研究，我們提出一個聚合反應機制，認為光照射初期形成一密度光柵和吸收光柵，可將繞射效率提升而量得第一波峰，其餘繞射波峰則是聚合光柵和吸收光柵相互加成的結果。利用此反應機制模型配合繞射理論公式，模擬所得的動態繞射曲線和量測結果有著相當程度的符合。
實驗II是全向光柵形成後，可做成光開關元件其機制之探討。利用單一氬離子雷射做為加熱光源，氦-氖雷射做為偵測光束，結果顯示氬離子雷射照射樣品時，第一階繞射效率有著顯著的增加。此變化我們認為主要是由熱膨脹效應所引起。光柵受熱形變，聚合物聚集較密處會擠壓液晶顆粒，使液晶分子整體有秩序的偏轉，如此造成聚合物聚集較密處和液晶聚集較密處相對折射率增加，所以繞射效率隨之增加。
實驗III其材料如同實驗I，利用單一氬離子雷射照射樣品時可形成繞射同心圓圖形。其成因是樣品中未溶解的微小顆粒可散射光線，這些散射光線經樣品後面玻璃反射後彼此間相互干涉而把PDLC薄膜硬化。樣品硬化完全後氬離子雷射又可當重建光源 ，重建此繞射同心圓影像。本實驗影像的記錄和重建僅需一道氬離子雷射，這和傳統全像術有著相當的不同。

Abstract
There are three major experiments in this thesis. The first experiment is to study the dynamical behavior of the first-order diffraction efficiency of gratings formed in polymer-dispersed liquid crystal films (PDLC) doped with a guest-host dye. Gratings were formed in PDLC films fabricated with various LC-polymer mixtures, and cured with different intensities. The results show that there are several peaks in the curve of the first-order diffraction efficiency versus time. From the light scattering studying, it is believed that the first peak is due to the density grating and absorption grating. The density grating is due to an amount of molecules gathering in the high-intensity regions. The absorption grating is resulted from the polymerization reaction that produces a large amount of free electrons in the high-intensity regions. The other peaks are caused by the superposition of absorption and phase grating. The phase grating is generated by the phase separation of LCs and monomers during the polymerization process. Based on the results obtained from the light scattering experiment, we proposed a model to explain the experimental results. The theory derived from this model is found to fit the results well.
The second experiment is following the grating formation it is irradiated by a single Ar+ laser beam while probed by a He-Ne laser. Experimental results indicate that the first-order diffracted intensity of the probe beam significantly increases. Such an optically switchable diffraction effect is attributed to thermal expansion. The G-206 dye absorbs Ar+ laser, subsequently resulting in thermal expansion. The liquid crystal (LC) droplets are then squeezed so that the LC molecules within the droplets are reoriented collectively. Thus, the refractive index difference between the LC-rich and polymer-rich stripes, Δn, increases.
The third experiment is studying the generated holographic ring patterns by a single beam (Ar+ laser) incident onto a polymer-dispersed liquid crystal (PDLC) film. The incident laser beam initially acts as a writing beam, and then induces “point” light sources due to micron-sized particles in the film. Interference between the incident beam and the induced “point” light sources then produces holographic ring patterns, which are permanently recorded in situ on the film. After recording, the incident beam becomes a reference beam and reconstructs the “point” source wavefronts. The interference among these reconstructed “point” light sources produces a Quetelet-type scattering ring in a screen placed behind the PDLC film.

封面
目錄
圖表索引
中文摘要
英文摘要
第一章 緒論
1-1液晶物理
1-1.1液晶分類
1-1.2光學異向性
1-1.3溫度對向列相液晶的影響
1-2聚合物化學
1-3PDLC薄膜光學特性
1-3.1PDLC反應動力學
1-3.2客主型染料/液晶薄膜
1-4論文概要
第二章 理論
2-1 雷射引致光柵
2-2 光柵物理
2-2.1光柵的分類
2-2.2體積光柵和薄膜光柵的特性探討
2-2.3Bragg 或Raman-Nath光柵之判斷準則
2-3 Raman-Nath繞射公式的推導
2-4 PDLC全像光柵形成的機制
第三章 實驗準備
3-1 材料介紹
3-2 樣品製作
第四章 實驗I:聚合物/液晶混合薄膜添加染料分子做成全像光柵時其動態繞射效率的研究
4-1實驗裝置
4-2結果與討論
第五章實驗II:利用聚合物/液晶混合材料添加染料分子做成可光開關式的全像光柵其特性研究
5-1實驗裝置
5-1.1測試光開關效應
5-1.2檢測光開關之物理意義
5-1.3光柵表層結構之觀測
5-2結果與討論
第六章 實驗III:利用單一光源記錄聚合物/液晶混合薄膜產生繞射全像
6-1實驗裝置
6-2結果與討論
第七章 總結與展望
參考文獻
附錄
論文著作

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