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系統識別號 U0026-2208201418462700
論文名稱(中文) 溫控轉換雷射模態於可空間調控膽固醇液晶模板之研究與應用
論文名稱(英文) Thermally-controlled laser-mode conversion based on spatially tunable photonic bandgap cholesteric liquid crystal templates
校院名稱 成功大學
系所名稱(中) 光電科學與工程學系
系所名稱(英) Department of Photonics
學年度 102
學期 2
出版年 103
研究生(中文) 林星玗
研究生(英文) Hsin-Yu Lin
學號 L76011142
學位類別 碩士
語文別 英文
論文頁數 88頁
口試委員 指導教授-李佳榮
口試委員-莫定山
口試委員-李偉
口試委員-鄭協昌
口試委員-黃宣瑜
中文關鍵字 膽固醇液晶模板  空間可調控性  雷射模態轉換  隨機雷射  能隙邊緣雷射 
英文關鍵字 cholesteric liquid crystal polymer template  spatial tunability  laser-mode conversion  random laser  bandedge lasing emission 
學科別分類
中文摘要 本論文成功發展可溫控轉換雷射模態之可空間調控回灌型膽固醇液晶模板雷射元件,此雷射元件之製作經由四個製程階段完成: 聚合硬化前、聚合硬化後、洗掉後與重灌後四階段。實驗結果顯示此元件之光子能隙可空間調控範圍幾乎涵蓋整個白光區域 (405 nm 至 752 nm),而且其可空間調控雷射模態可於較低溫之隨機雷射模態與較高溫之能隙邊緣雷射模態作轉換。當模板回填之染料摻雜向列型液晶處於較低溫之向列態時,由於位於奈米孔洞之向列態液晶與模板間折射率不匹配會造成受激產生的螢光經過多重散射造成增益放大,而產生隨機雷射;當回填液晶處於較高溫之各向同性態時,液晶與模板間折射率匹配使得模板之膽固醇光子能隙結構顯現,進而產生能隙邊緣模式雷射輸出。
  此外,在經過反向自然擴散產生具有螺距梯度之膽固醇樣品製成的回灌型模板雷射會產生許多缺點,例如結構缺陷多、雷射閥值相對較高、雷射線寬相對較寬、可空間調控範圍相對較窄、製程時間長;實驗結果顯示,於擴散過程伴隨利用快速熱退火技術可使得製成具有螺距梯度之回灌型膽固醇液晶模板雷射之結構與雷射特性皆改善許多;尤其,最低雷射能量閾值更可低至60 nJ/pulse。本元件由於具有許多優勢,如結構穩定且無缺陷、低雷射閥值、可廣頻域空間調控且可雷射模態轉換之雷射特性,相信其在未來具有相當潛力可應用於光電子學與顯示器等領域。
英文摘要 A spatially tunable dye-doped liquid crystal (DDLC) refilling cholesteric liquid crystal (CLC) polymer template device with a thermally controlled laser-mode conversion is successfully developed in this study. This laser device is fabricated through four stages: before curing, after curing, after washing out, and after refilling. Experimental results show that the tunable spectral range for the photonic bandgap (PBG) of the laser device covers nearly the entire white region (405 nm to 752 nm). The spatially tunable laser mode can be converted between random lasing operation at low temperatures and bandedge lasing operation at high temperatures. The mismatch between the refractive indices of the refilling nematic LC (NLC) in the nanopores and the template leads to multiple scattering of pumped fluorescence emission and to random lasing. After the refilling LCs become isotropic, the index match between the LC and the template causes the PBG of the template to appear and results in bandedge lasing emission.
The refilling template laser fabricated by forming a gradient-pitched CLC through nature diffusion has many drawbacks, including the formation of defects, relatively high energy threshold, wide linewidth, narrow tunable spectral range, and long processing time. The experimental results show that the structural and lasing features of the gradient-pitched refilling CLC template laser improve if rapid thermal annealing is repeatedly adopted during thermal diffusion, particularly the ultralow energy threshold of 60 nJ/pulse. The developed device has many advantages, such as having a highly stable and defect-free structure, an ultralow lasing threshold, and wide spatial tunability and lasing-mode convertibility. Hence, the device has high application potential in photonics and display.
論文目次 摘要 I
Abstract II
Acknowledgements IV
List of Figures V
List of Tables XII
Contents XIII
Chapter one Introduction 1
Chapter Two Properties of Liquid Crystals 4
2-1 Introduction to Liquid Crystals 4
2-2 Classification of Liquid Crystals 5
2-2-1 Lyotropic Liquid Crystals 5
2-2-2 Thermotropic Liquid Crystals 5
2-3 Physical Properties of Liquid Crystals 9
2-3-1 Optical Anisotropy 10
2-3-2 Dielectric Anisotropy 13
2-3-3 Elastic Continuum Theory of Liquid Crystals 14
Chapter Three Cholesteric Liquid Crystal and Polymer Templates 16
3-1 Optical Properties of Cholesteric Liquid Crystals 16
3-2 Factors Influencing on Helical Pitch 18
3-2-1 Temperature 18
3-2-2 Concentration of chiral dopants 18
3-2-3 Magnetic and Electric Field 19
3-2-4 Optical Field 21
3-3 Cholesteric Liquid Crystal Polymer Templates 21
3-3-1 Backgrounds of Cholesteric Liquid Crystal Polymer Templates 21
3-3-2 Wash-Out/Refill Technique 23
3-4 Tunability of Cholesteric Liquid Crystal Polymer Templates 25
3-4-1 Electric Field 25
3-4-2 Temperature 27
3-4-3 Optical Field 28
Chapter Four Laser mechanism 30
4-1 Basic Principles of Lasers 30
4-1-1 Interactions between Photons and Atoms 30
4-1-2 Population Inversion 33
4-1-3 Process of Lasing Emission 36
4-2 Distributed Feedback Lasers 37
4-3 Photonic Band-Edge Lasers of Cholesteric Liquid
Crystals 38
4-4 The Introduction of Random Lasers 40
4-4-1 Mechanism of Random Lasers 40
4-4-2 Classification of random lasers 41
4-4-3 Random Lasers of Liquid-Crystal-Based Materials 43
Chapter Five Sample Fabrication and Experimental
Setups 46
5-1 Materials 46
5-2 Sample Fabrication 50
5-2-1 Preparation of Glass Substrates 51
5-2-2 Fabrication of Empty Cells 52
5-2-3 Mixtures for Fabrication of CLC Polymer templates 52
5-2-4 Fabrication of DDNLC-refilling CLC Polymer template cells 54
5-3 Experimental setups 59
Chapter Six Results and Discussion 61
6-1 Spatially-Tunable PBG of DDNLC-Refilling CLC Polymer Template Sample at Various Stages 61
6-2 Laser-Mode Convertible and Spatially-Tunable DDNLC-Refilling CLC Template Laser 64
6-2-1 Spatially-Tunable Laser Modes of a Refilling CLC Template Laser 64
6-2-2 Mechanisms for the Laser-Mode Conversion 68
6-3 Refined DDNCL-refilling CLC Template Laser Through Thermal Diffusion and Rapid Thermal Annealing 70
6-3-1 Linear Distribution of Photonic Band Gaps 70
6-3-2 Widely Tunable Range of Lasing Emissions 73
6-3-3 Lasing Emissions with Ultralow Energy Threshold 76
Chapter Seven Conclusion and Future works 82
7-1 Conclusion 82
7-2 Future works 83
Reference 84
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