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| 研究生： |
李佳榮 Lee, Chia-Rong |
|---|---|
| 論文名稱： |
添加偶氮染料分子聚合物球型之『聚合物-液晶』混合薄膜作為全像光柵記錄的研究與應用 Studies of Holographic Grating Recordings and Their Applications based on Azo-Dye-Doped Polymer-Ball-Type Polymer-Dispersed Liquid Crystal Films |
| 指導教授： |
傅永貴
Fuh, Ying-Guey |
| 學位類別： |
博士 Doctor |
| 系所名稱： |
理學院 - 物理學系 Department of Physics |
| 論文出版年： | 2003 |
| 畢業學年度： | 91 |
| 語文別： | 英文 |
| 論文頁數： | 94 |
| 中文關鍵詞： | 液晶 、聚合物 、偶氮染料 、全像光柵 、吸附 |
| 外文關鍵詞： | azo-dye, polymer, liquid crystal, adsorption, holographic grating |
| 相關次數： | 點閱：63 下載：4 |
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由於奇特的異向性質，一些物質（如偶氮染料）近年來越來越受到科學家們的重視。許多研究學者將偶氮染料添加於某些如聚合物與/或液晶等有機物質內形成主客系統進而發現及研究許多因主客互相耦合而產生的有趣現象。最重要的現象莫過於所謂的光致分子轉向效應。總括來說這個效應可能由以下幾個效應產生：光折變效應、Janossy效應及光致同份異構化效應。在這本論文中我們所使用的系統是添加偶氮染料之聚合物與液晶混合薄膜。我們的目標除了要研究在這個系統裡所發生的有趣物理機制之外，研發可控制之全像元件的製造及其應用亦是我們討論的課題。
在這本論文中，我們研究的主題大致上可分為兩部份。第一部份是添加偶氮染料分子聚合物球型之『聚合物-液晶』混合薄膜在強度全像光柵的研究與其應用。主要地，我們成功地藉由簡單的強度全像技術於我們的系統製作了兩個非傳統型的可控制全像光柵元件。這樣的光柵可分成兩到階段完成；第一階段是將添加與未添加了偶氮染料的兩個『聚合物-液晶』混合材料薄膜以紫外光照射使其經相分離過程後均形成聚合物球均勻分佈的聚合物球型PDLC。第二階段再以兩道氬離子雷射光的疊加照射，於此兩PDLC薄膜中各自形成一個潛伏於散射中的聚合物密度光柵。這樣的光柵是由於可選擇性的二次光聚合反應形成的。適當地藉由各加熱或外加電壓於此兩光柵時，潛伏的聚合物密度光柵會因液晶與聚合物折射率的相配而顯現出來。若更進一步地觀測所產生的一階繞射效率與溫度、外加電壓及入射光線偏振方向的關係，則可發現有添加與未添加染料的光柵其實驗結果差異很大。這樣的差異是由於在添加染料的光柵元件內，經光激發而吸附於聚合物球上的偶氮染料分子引致周圍液晶分子一致轉向效果所形成的。液晶與染料分子最後傾向垂直於激發光線偏振方向及傳播方向。因此，藉由外加熱或電場，此添加染料的光柵元件可於一個與偏振有關與無關的光柵間做切換。
在研究全像光柵上另一個部分是偏振全像光柵。偏振全像技術對研究異向性物質是一個相當重要的方法。具有偏振選擇性的偏振全像光柵經常可用在影像處理及測偏振元件的應用上。基於此點我們將研究內容的第二部分著眼於添加偶氮染料分子聚合物球型之『聚合物-液晶』混合薄膜在偏振全像光柵的研究及測偏振元件應用上。我們證明了添加偶氮染料的『聚合物-液晶』混合薄膜可用兩道線偏振相垂直(s-及p-偏振)的連續激發雷射光束疊加來製成偏振光柵。此偏振光柵是由於偶氮染料受激發光干涉場偏振狀態呈週期性分佈(光強一定)激發所致。這些受激的染料分子經歷了光致同份異構化、轉向效果、擴散作用直到最後吸附在聚合物球表面上，並同時觸發了液晶分子呈週期性轉向。經過實驗結果的分析發現所得的偶數與奇數階繞射光束其偏振與入射光的偏振有關。因此，此偏振光柵可因入射光偏振的不同而作成偏振或非偏振分光器。更甚者，我們使用瓊斯矩陣方法與向量繞射理論來發展經偏振光柵所得繞射光偏振特性的模擬，所得結果與實驗值吻合。另外，我們亦使用了兩道時寬為20奈秒、總能量為15mJ/cm2單脈衝雷射光作為激發光束製作了一個可於2ms內快速記錄的偏振光柵。其特性及形成的機制與使用連續激發光源製成的偏振光柵相似。此可快速記錄的偏振光柵可電切換，然而若經熱處理則有部份可被消除掉；此現象可能是由於吸附作用較弱的部份染料分子經熱干擾後脫附導致記憶效果降低所致。
Some materials (e. g. azo derivatives) have been intensively studied because of their peculiar anisotropic properties. Many researchers added azo derivatives into some organic materials, e. g. polymers and/or liquid crystals, to form the guest-host systems and dedicated in the investigation of many interesting effects through the coupling of the guest and the host. The most significant effect in such guest-host systems is the photo-induced molecular reorientation effect, which conclusively results from the photorefractive effect, Janossy effect, and/or photoisomerization effects. The aims of this thesis work are, in addition to the studies of the interesting physics occurred in the system of polymer-dispersed liquid crystals doping with azo dyes, the fabrications of controllable holographic elements and the studies of their applications.
This thesis contains mainly two parts. The first part is the study of holographic gratings and their switching applications based on azo-dye-doped Polymer-Ball-Type Polymer-Dispersed Liquid Crystal (PBT-PDLC) films. Primarily, we successfully fabricate two unconventional controllable intensity holographic gratings based on the azo-dye-doped and undoped PBT-PDLC films. The next step photo-polymerization of the LC/prepolymer composites with the superposing illumination of two Ar+ laser beams after UV irradiation is demonstrated to produce a latent density grating. Such a grating is formed by selective secondary photo-polymerization and hidden in the light-scattering PBT-PDLC sample at room temperature. Matching the indices of LCs and polymer by heating or applying a voltage can make the density grating appear. The measured variations of diffraction efficiencies with temperature, voltage and states of polarization of diffracted beams in dye-doped and undoped cells show that the dye-doped grating is quite different from the undoped one. The discrepancy is attributable to the reorientation effect of LCs through their interaction with the photo-induced adsorption of the doped dyes on the surface of polymer balls in the dye-doped cell. The final orientation of LCs and dyes tend to be orthogonal to the polarization and propagation directions of the pump beams. The doped grating, therefore, can be thermally or electrically switched between a polarization-dependent and -independent grating.
The second part is the study of the polarization grating (PG) in the doped PBT-PDLC system. Polarization holography is an important technique for investigating the anisotropic materials. The polarization selectivity of a PG makes them promising for uses in images processing and polarimetric components, etc.; this part of research, therefore, is focused on the study of polarization holographic gratings and their polarimetric applications based on azo-dye-doped PBT-PDLC films. We demonstrate that the azo-dye-doped PBT-PDLC films can be served to fabricate polarization gratings (PGs) written by two orthogonally (s- and p-) polarized writing beams originated from a cw laser. The formation of the PG is attributable to that the interfering light field with a spatial variation of polarization states and constant intensity excited the azo-dye molecules. They undergo the photoisomerization, reorientation, diffusion and then adsorb on the surfaces of the polymer balls, and finally reorient the LCs. Analyses of the measured results show that the polarization of the diffracted beams depends on that of the incident light. Therefore, the PGs can be served as polarized or unpolarized beam splitters, depending on the polarization of incident light. A model based on the Jones matrix method and the vectorial diffraction theory is developed and fit well with the experimental results. Finally, an optical recording of the PG is achieved in ~ 2ms by using single pulse laser beams, having a duration of ~ 20ns and a total energy density of ~15mJ/cm2. The properties and mechanism of the formed PG are similar to those by using cw pump beams. Such a fast recorded PG is electrically switchable, and partially erasable by thermal treatment. Parts of dye molecules with weaker adsorption desorb probably from the surface of the polymer balls, because of thermal disturbance, which bring about a partially-erasable PG.
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校內：立即公開校外：2002-10-07公開