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研究生:吳柏辰
研究生(外文):Po-ChenWu
論文名稱:染料摻雜液晶注入毛細管產生雷射輸出之研究及應用
論文名稱(外文):Investigation of lasing emissions in dye-doped liquid crystal infiltrated capillary cylinder and their applications
指導教授:李佳榮
指導教授(外文):Chia-Rong Lee
學位類別:碩士
校院名稱:國立成功大學
系所名稱:光電科學與工程學系
學門:工程學門
學類:電資工程學類
論文種類:學術論文
論文出版年:2012
畢業學年度:100
語文別:英文
論文頁數:70
中文關鍵詞:液晶隨機雷射回音廊模態雷射光致異構化效應
外文關鍵詞:liquid crystalrandom lasingwhispering-gallery mode lasingphotoisomerization
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本論文研究首次發現並探討染料摻雜液晶注入毛細管之可全光控雷射現象與應用。實驗結果顯示此雷射元件具有雙雷射模態— 隨機雷射與回音廊模態雷射。藉由將激發脈衝聚焦在毛細管液晶區中央與邊緣位置可達到切換此兩種不同雷射模態效果。
除此之外,當摻雜偶氮染料於液晶時,此雷射器不僅可藉位移激發位置以切換兩種雷射模態,還可實現全光調控雷射輸出。此雷射器之隨機雷射與回音廊雷射模態之輸出特性可藉由交替照射紫外光和綠光來加以控制。照射紫外光時偶氮染料會發生trans到 cis 形態之同素異構化反應,進而引致液晶之等溫相變(向列相等溫轉變為istropic相);而照射綠光將讓偶氮染料從 cis 回復到 trans態,並引致液晶從isotropic相變回向列相。在此等溫相變過程中,液晶區域的有序性跟介電性會受到影響,並引致隨機雷射輸出強度變化。同時由於等溫相變會導致材料的吸收與螢光頻譜相對之變化,造成回音廊模態雷射輸出波長之變化。

This study investigates for the first time an all-optically controllable laser device based on a dye-doped liquid crystal (DDLC) infiltrated capillary cylinder. This laser capillary can be operated between two various lasing modes, the random lasing and the whispering-gallery mode (WGM) lasing, by changing the focusing position of the pumped pulses on the center or the periphery of the LC region of the capillary.
With the addition of the azo dye in the DDLC of the laser capillary, not only the interchangeability between the two types of lasing modes but also all-optically controllability for the laser can be achieved. The random and WGM lasings can be controlled by successively irradiating one UV and one green beams on the laser capillary. The mechanism of the all-optical controllability of the laser capillary is attributed to the isothermal nematic(N)→isotropic(I) and I→N phase transitions of LCs, respectively, due to UV-light-induced trans→cis and green-light-induced cis→trans back isomerizations of the azo dye. During the process of isothermal N←→I phase transition of LCs, the spatial fluctuation of the order and thus of the dielectric tensor in LCs may vary, which may alter the scattering strength of the light in LCs and thus the intensity of the generated random lasing. In addition to the optical modulation for the intensity of the random lasing, the wavelength of the WGM lasing can be tuned via photoinduced isothermal N←→I phase transition in virtue of the relative variations of the absorption and the emitted fluorescence spectra of the laser dye.
摘 要 I
Abstract II
Acknowledgements III
Table of Contents IV
List of Figures VII
List of Tables XIII

Chapter One Introduction 1

Chapter Two Properties of liquid crystal 4
2.1 Discovery of liquid crystal 4
2.2 What is liquid crystal ? 4
2.3 Classification of liquid crystal 5
2.4 Physical properties of liquid crystals 8

Chapter Three Fundamentals of laser and photosensitive materials 14
3.1 Theory of laser 14
3.2 Random laser 20
3.2.1 Mechanism of random laser 20
3.2.2 Classification of random laser 21
3.2.3 The multiple scattering and random lasing effects in nematic liquid crystals 22
3.3 Whispering-gallery mode lasing 24
3.3.1 Background of whisper-gallery mode 24
3.3.2 Basic properties of whisper-gallery mode 25
3.4 Photosensitive material 27
3.4.1 Photochromism 27
3.4.2 Photoisomerization of azobenzene derivatives 29
3.4.3 Photo-induced isothermal phase transition of azo-dye-doped liquid crystals 30

Chapter Four Sample preparation and experimental setup32
4.1 Materials and sample fabrication 32
4.1.1 Materials 32
4.1.2 Fabrication of DDLC capillary cylinder sample 36
4.2 Experimental setups 38
4.2.1 Setup for measuring the lasing emissions in DDLC capillary cylinder samples 38
4.2.2 Setup for measuring the all-otically controllable lasing emissions in azo-dye-added DDLC capillary cylinder samples 40

Chapter Five Results and discussion 41
5.1 Random lasing emission of dye-doped liquid crystal 41
5.1.1 Random lasing emission in dye-doped liquid crystal infiltrated capillary cylinder 42
5.1.2 Polarization of random lasing emission in dye-doped liquid crystal infiltrated capillary cylinder 45
5.2 Measuring whispering gallery mode laser 48
5.2.1 Whispering gallery mode lasing emission in dye-doped liquid crystal infiltrated capillary cylinder 48
5.2.2 Polarization of whispering gallery mode lasing emission in dye-doped liquid crystal infiltrated capillary cylinder 51
5.3 Lasing emissions at different pumped locations 52
5.4 All-optically controllable random lasing emission and whispering gallery mode lasing emission based on dye-doped liquid crystal infiltrated capillary cylinder with doping azo-dye 57
5.4.1 All-optically controllable random lasing emission in the capillary cylinder 57
5.4.2 All-optically controllable whispering gallery mode lasing emission in the capillary cylinder 62

Chapter Six Conclusion and Future works 66
6.1 Conclusion 66
6.2 Future works 67

List of Reference 68

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