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Title: | 於染劑參雜液晶中實現光控制二倍頻與其在超解析顯微鏡之應用 Optical controllable second harmonic generation based on dye-doped liquid crystal film and its application to super resolution microscopy |
Authors: | Kuan-Chieh Chen 陳冠杰 |
Advisor: | 朱士維(Shi-Wei Chu) |
Keyword: | 二倍頻,液晶,抑制,光控制,超解析顯微術, second harmonic generation,liquid crystal,suppression,optically control,superresolution microscopy, |
Publication Year : | 2014 |
Degree: | 碩士 |
Abstract: | 不論電控制或是光控制二倍頻皆被應用於光通訊和光儲存技術上。相較於電控制二倍頻,光控制二倍頻不但有更高的準確性,同時在控制的圖樣上也有更多的自由度。然而過往光控制二倍頻的結果有著些許壞處,包括低開關對比、有限的開關次數和較長的反應時間。
在這篇論文中,我們提出於染劑參雜液晶中利用光致轉變達成光控制二倍頻。和之前的光控制二倍頻比起來,這個方法不但可以重複開關,還有80%的調製深度以及秒以下的反應時間。 此外我們也提出兩個可能的機制。包括optical Fredericks 轉變和nematic-isotropic 相轉變。經過實驗證實,後者比較可能為主要機制。由於二倍頻無法在isotropic相中產生。藉由此特性,二倍頻可以有效被抑制達到高開關對比。另一方面,因為液晶的分子特性,反應時間相較於之前的實驗大幅縮短。最後,因為液晶並沒有產生任何化學變化,所以這是個可重複開關的光控制二倍頻。 在論文的最後,我們也提出光控制二倍頻的新應用─超解析顯微術。Reversible saturable optical fluorescence transitions (RESOLFT) microscopy雖然已是一個成熟的技術,但由於其建立在螢光的開關。所以不可避免的光漂白和有限的開關次數成為一個待解決的問題。由於二倍頻並不會有光漂白的問題,所以光控制二倍頻很有機會取代螢光作為超解析顯微術的核心機制。 In the past, electrically or optically controllable second harmonic generation (SHG) has been applied to optical communication and storage. Compared with electrical control, optical one permits not only higher precision but also higher freedom in forming control pattern. However, previous methods of optically controllable SHG suffer from several drawbacks, including low on-off contrast, limited switch cycles and very long response time. Here, we demonstrate a new idea of optically controllable SHG based on the light-induced transition of dye-doped liquid crystal (DDLC) film. Compared with other optical methods, it is a reversible switch with 80-percent modulation depth and second-scale response time. There are two possible mechanisms for this high-contrast, high-speed SHG switch, including optical Fredericks transition and nematic-isotropic phase transition. Based on transmittance, which is not altered by light, we have determined that nematic-isotropic phase transition is more likely the dominant mechanism. Because SHG is not allowed in isotropic phase and the dynamic motion of liquid crystal is much sooner than the materials, which were used in previous results, high-contrast and high-speed controllable SHG is realized. Besides, it is a reversible switch since chemical action is not involved in liquid crystal. With the capability to optically switch on/off an optical signal, one novel application is superresolution microscopy. Reversible saturable optical fluorescence transitions (RESOLFT) microscopy, one of superresolution technics, is based on reversible switch of fluorescence. However, fluorescence suffers from photobleaching and the limit of switching cycles. On the other hand, SHG from liquid crystal does not exhibit bleaching effect at all. Therefore, with similar scheme of RESOLFT microscopy, repeatable optically controllable SHG has potential in super resolution microscopy. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/8007 |
Fulltext Rights: | 同意授權(全球公開) |
Appears in Collections: | 物理學系 |
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