探討黑爾弗里希形變對膽固醇液晶之穿透及反射頻譜調制;Investigations of transmissive and reflective spectra of cholesteric liquid crystals modulated by Helfrich deformation

Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/89443

Title:	探討黑爾弗里希形變對膽固醇液晶之穿透及反射頻譜調制;Investigations of transmissive and reflective spectra of cholesteric liquid crystals modulated by Helfrich deformation
Authors:	程素慧;Cheng, Su-Hui
Contributors:	光電科學與工程學系
Keywords:	黑爾弗里希形變;貝里曼矩陣;帶寬變化;Helfrich deformation;Berreman 4 × 4 matrix;bandwidth variation
Date:	2022-09-15
Issue Date:	2022-10-04 11:15:17 (UTC+8)
Publisher:	國立中央大學
Abstract:	本論文研究主要探討黑爾弗里希形變(Helfrich deformation)的膽固醇液晶之頻譜特徵及其原因，分為兩部分主題，第一部分為分析在不同物理參數下，對Helfrich deformation的膽固醇液晶之影響，藉由量測外加電壓下的穿透頻譜及觀察偏光顯微鏡下的結構，確立各條件下Helfrich deformation出現之電壓值，並比較各條件之反射波段變化，討論其差異及原因。在此部分研究透過改變液晶盒厚度、配向膜種類及濃度配比參數，發現摻雜液晶二聚體的膽固醇液晶，可降低Helfrich deformation出現之電壓值，且各條件之穿透頻譜皆具有頻譜拓寬效果，並且水平配向可增強此效果。本論文第二部分主題為分析Helfrich deformation的膽固醇液晶之頻譜特徵，此頻譜特徵與以往膽固醇液晶不同，其反射波段於穿透頻譜及反射頻譜不同，本論文對此現象的推論為此結構中產生類似波導作用，透過貝里曼4 × 4矩陣模擬以佐證，並將膽固醇液晶結構分為三層結構進行討論，分別為中間層的Helfrich deformation結構與接近基板的兩層邊界層一般膽固醇液晶平面態結構，從模擬頻譜圖了解各層結構間發生的穿透及反射，而在邊界層與中間層間反射光因Helfrich deformation的結構特性，發生來回反射的現象，使Helfrich deformation的膽固醇液晶之反射波段，在反射頻譜與穿透頻譜不同。;In this thesis, we mainly investigate the spectral characteristics and their root causes of cholesteric liquid crystals (CLCs) with Helfrich deformation. The research topic includes the following two parts. In the first part, we analyze the influences of different physical parameters on the CLCs with Helfrich deformation. According to the measured transmissive spectra of the CLCs applied with electric fields and the observed images under a polarized optical microscopy, the threshold voltage of the Helfrich deformation in each condition can be confirmed. In addition, we also elucidate the differences between them and the corresponding reasons according to the changes of the reflection bands. Furthermore, by varying the cell gap, alignment film, and concentration of the adopted materials, it is found that the CLCs doped with liquid crystal dimer have a lower threshold voltage of the Helfrich deformation, and the transmission spectrum of each condition possesses the feature of broadening the reflection band width. Besides, the homogenous alignment layer can enhance this effect. In the second part, we analyze the spectral characteristics of CLCs with Helfrich deformation, which differ from those of the previous CLCs. The obtained wavelength bands of the transmission spectra and the reflection spectra are different. The cause of this phenomenon can be verified by the Berreman 4 × 4 matrix simulation, and be concluded to be similar to waveguide effect due to such structures. The CLC structures are divided into three layers for simple discussion, namely the middle layer with the Helfrich deformation structure and the boundary layers closed to the substrates with general planar textures of CLCs. The transmission and reflection between the layers of the structures can be clarified from the simulated spectra. Due to the structural characteristics of the Helfrich deformation, the reflected light is reflected back and forth between the boundary layers and the middle layer, so the wavelength bands of the measured reflection and transmission spectra of CLCs with Helfrich deformation are different.
Appears in Collections:	[Graduate Institute of Optics and Photonics] Electronic Thesis & Dissertation

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