臺灣博碩士論文加值系統

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。

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.

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

1.H. Kogelnik, and C. V. Shank, “Coupled-wave theory of distributed feedback lasers, Journal of Applied Physics 453, 2327‒2335 (1972).

2.V. I. Kopp, Z.-Q. Zhang, and A. Z. Genack, “Lasing in chiral photonic structures, Progress in Quantum Electronics 27, 369‒416 (2003).

3.D. C. O'Shea, W. R. Callen, and W. T. Rhodes, Introduction to Lasers and Their Applications (Addison Wesley, Boston, 1977).

4.F. Castles, F. V. Day, S. M. Morris, D. H. Ko, D. J. Gardiner, M. M. Qasim, S. Nosheen, P. J. Hands, S. S. Choi, R. H. Friend, and H. J. Coles, “Blue-phase templated fabrication of three-dimensional nanostructures for photonic applications, Nature Materials 11, 599‒603 (2012).

5.J. Guo, H. Wu, F. Chen, L. Zhang, W. He, H. Yang, and J. Wei, “Fabrication of multi-pitched photonic structure in cholesteric liquid crystals based on a polymer template with helical structure, Journal of Materials Chemistry 20, 4094 (2010).

6.A. Muñoz, M. E. McConney, T. Kosa, P. Luchette, L. Sukhomlinova, T. J. White, T. J. Bunning, and B. Taheri, “Continuous wave mirrorless lasing in cholesteric liquid crystals with a pitch gradient across the cell gap, Optics Letters 37, 2904‒2906 (2012).

7.M. E. McConney, V. P. Tondiglia, J. M. Hurtubise, L. V. Natarajan, T. J. White, and T. J. Bunning, “Thermally induced, multicolored hyper-reflective cholesteric liquid crystals, Advanced Materials 23, 1453‒1457 (2011).

8.M. E. McConney, T. J. White, V. P. Tondiglia, L. V. Natarajan, D.-k. Yang, and T. J. Bunning, “Dynamic high contrast reflective coloration from responsive polymer/cholesteric liquid crystal architectures, Soft Matter 8, 318 (2012).

9.C.-C. Chien, J.-H. Liu, and A. V. Emelyanenko, “Fabrication and characterization of imprinted photonic crystalline polymer matrices via multiple UV polymerizations, Journal of Materials Chemistry 22, 22446 (2012).

10.M. E. McConney, V. P. Tondiglia, J. M. Hurtubise, T. J. White, and T. J. Bunning, “Photoinduced hyper-reflective cholesteric liquid crystals enabled via surface initiated photopolymerization, Chemical Communications 47, 505‒507 (2011).

11.S. S. Choi, S. M. Morris, W. T. Huck, and H. J. Coles, “Simultaneous red-green-blue reflection and wavelength tuning from an achiral liquid crystal and a polymer template, Advanced Materials 22, 53‒56 (2010).

12.P. G. d. Gennes, and J. Prost, The Physics of Liquid Crystals (Clarendon Press, Oxford, 1993).

13.C. V. Yelamaggad, G. Shanker, U. S. Hiremath, and S. Krishna Prasad, “Cholesterol-based nonsymmetric liquid crystal dimers: an overview, Journal of Materials Chemistry 18, 2927‒2949 (2008).

14.K. Busch, S. Lölkes, R. B. Wehrspohn, and H. Föll, “Photonic Crystals : Advances in Design, Fabrication, and Characterization, (Wiley-VCH, Weinheim, Germany, 2004).

15.S.-T. Wu, and D.-K. Yang, Reflective Liquid Crystal Displays (John Wiley ＆ Sons Ltd., Chichester, England, 2001).

16.H. Choi, J. Kim, S. Nishimura, T. Toyooka, F. Araoka, K. Ishikawa, J. W. Wu, and H. Takezoe, “Broadband Cavity-Mode Lasing from Dye-Doped Nematic Liquid Crystals Sandwiched by Broadband Cholesteric Liquid Crystal Bragg Reflectors, Advanced Materials 22, 2684 (2010).

17.I. C. Khoo, Liquid Crystals: Physical Properties and Nonlinear Optical Phenomena (John Wiley ＆ Sons, New York, 1995).

18.S.-H. Lin, C.-Y. Shyu, J.-H. Liu, P.-C. Yang, T.-S. Mo, S.-Y. Huang, and C.-R. Lee, “Photoerasable and photorewritable spatially-tunable laser based on a dye-doped cholesteric liquid crystal with a photoisomerizable chiral dopant, Optics Express 18, 9496‒9503 (2010).

19.T. J. White, R. L. Bricker, L. V. Natarajan, V. P. Tondiglia, C. Bailey, L. Green, Q. Li, and T. J. Bunning, “Electromechanical and light tunable cholesteric liquid crystals, Optics Communications 283, 3434‒3436 (2010).
20.K. Ki-Han, S. Dong Han, S. Zheng-Guo, P. Byung Wok, P. Kyoung-Ho, L. Joun-Ho, and Y. Tae-Hoon, “Fast switching of long-pitch cholesteric liquid crystal device, Optics Express 19, 10174‒10179 (2011).

21.L. Shin-Ying, and C. Liang-Chy, “A polymer-stabilized single-layer color cholesteric liquid crystal display with anisotropic reflection, Applied Physics Letters 91, 1‒3 (2007).

22.J. Guo, H. Cao, J. Wei, D. Zhang, F. Liu, G. Pan, D. Zhao, W. He, and H. Yang, “Polymer stabilized liquid crystal films reflecting both right- and left-circularly polarized light, Applied Physics Letters 93, 201901 (2008).

23.J. Xiang, and O. D. Lavrentovich, “Blue-phase-polymer-templated nematic with sub-millisecond broad-temperature range electro-optic switching, Applied Physics Letters 103, 051112 (2013)

24.B. E. A. Saleh, and M. C. Teich, Fundamentals of Photonics (John Wiley ＆ Sons, New York, 2007).

25.A. Yariv, and P. Yeh, Photonics, 6th ed. (Oxford University Press, New York, 2007).

26.J. T. Verdeyen, Laser Electronics, 3rd ed. (Prentice Hall, Inc., 1995).

27.沈柯, 雷射原理教程 (亞東書局, 臺北市, 1990).

28.H. Kogelnik, and C. V. Shank, “Stimulated emission in a periodic structure, Applied Physics Letters 18, 152 (1971).

29.H. Takezoe, Liquid Crystals Beyond Displays: Chemistry, Physics, and Applications (John Wiley ＆ Sons, Inc., New Jersey, 2012).

30.D. S. Wiersma, “The physics and applications of random lasers, Nature Physics 4, 359‒367 (2008).

31.N. M. Lawandy, R. M. Balachandran, A. S. L. Gomes, and E. Sauvain, “Laser action in strongly scattering media, Nature 368, 436‒438 (1994).


32.H. Cao, Y. G. Zhao, S. T. Ho, E. W. Seelig, Q. H. Wang, and R. P. H. Chang, “Random laser action in semiconductor powder, Physical Review Letters 82, 2278‒2281 (1999).

33.D. Wiersma, “Laser physics - The smallest random laser, Nature 406, 132 (2000).

34.V. M. Apalkov, M. E. Raikh, and B. Shapiro, “Random resonators and prelocalized modes in disordered dielectric films, Physical Review Letters 89, 016802 (2002).

35.R. C. Polson, and Z. V. Vardeny, “Random lasing in human tissues, Applied Physics Letters 85, 1289‒1291 (2004)
.
36.Q. H. Song, L. Wang, S. M. Xiao, X. C. Zhou, L. Y. Liu, and L. Xu, “Random laser emission from a surface-corrugated waveguide, Physical Review B 72 (2005).

37.D. Huang, E. A. Swanson, C. P. Lin, J. S. Schuman, W. G. Stinson, W. Chang, M. R. Hee, T. Flotte, K. Gregory, C. A. Puliafito, and J. G. Fujimoto, “Optical coherence tomography, Science 254, 1178‒1181 (1991).

38.B. Redding, M. A. Choma, and H. Cao, “Spatially Incoherent Random Lasers for Full Field Optical Coherence Tomography, CLEO: Laser Science to Photonic Applications, 1‒3 (2011).

39.B. Redding, M. A. Choma, and H. Cao, “Speckle-free laser imaging using random laser illumination, Nature Photonics 6, 497 (2012).

40.Y. J. Liu, X. W. Sun, H. I. Elim, and W. Ji, “Gain narrowing and random lasing from dye-doped polymer-dispersed liquid crystals with nanoscale liquid crystal droplets, Applied Physics Letters 89, 011111 (2006).

41.C. R. Lee, J. D. Lin, B. Y. Huang, T. S. Mo, and S. Y. Huang, “All-optically controllable random laser based on a dye-doped liquid crystal added with a photoisomerizable dye, Optics Express 18, 25896‒25905 (2010).

42.C. R. Lee, J. D. Lin, B. Y. Huang, S. H. Lin, T. S. Mo, S. Y. Huang, C. T. Kuo, and H. C. Yeh, “Electrically controllable liquid crystal random lasers below the Fréedericksz transition threshold, Optics Express 19, 2391‒2400 (2011).

43.S. Ferjani, A. De Luca, V. Barna, C. Versace, and G. Strangi, “Thermo-recurrent nematic random laser, Optics Express 17, 2042‒2047 (2009).

44.G. Strangi, S. Ferjani, V. Barna, A. De Luca, C. Versace, N. Scaramuzza, and R. Bartolino, “Random lasing and weak localization of light indye-doped nematic liquid crystals, Optics Express 14, 7737‒7744 (2006).

45.M. Glogarova, G. Strangi, S. Ferjani, V. Barna, A. De Luca, C. Versace, N. Scaramuzza, R. Bartolino, P. Palffy-Muhoray, and M. Copic, “Random lasing in dye doped nematic liquid crystals: the role of confinement geometry, Proceedings of the SPIE 6587, 65870‒65879 (2007).

46.S. Ferjani, V. Barna, A. De Luca, C. Versace, and G. Strangi, “Random lasing in freely suspended dye-doped nematic liquid crystals, Optics Letters 33, 557-559 (2008).

47.C.-W. Chen, H.-C. Jau, C.-T. Wang, C.-H. Lee, I. C. Khoo, and T.-H. Lin, “Random lasing in blue phase liquid crystals, Optics Express 20, 23978‒23984 (2012).

48.S. M. Morris, D. J. Gardiner, P. J. W. Hands, M. M. Qasim, T. D. Wilkinson, I. H. White, and H. J. Coles, “Electrically switchable random to photonic band-edge laser emission in chiral nematic liquid crystals, Applied Physics Letters 100, 071110 (2012).

49.R. Ozaki, T. Shinpo, and H. Moritake, “Improvement of orientation of planar cholesteric liquid crystal by rapid thermal processing, Applied Physics Letters 92, 163304 (2008).

50.M. Mitov, and N. Dessaud, “Going beyond the reflectance limit of cholesteric liquid crystals, Nature materials 5, 361‒364 (2006).

51.M. Mitov, and N. Dessaud, “Cholesteric liquid crystalline materials reflecting more than 50% of unpolarized incident light intensity, Liquid Crystals 34, 183‒193 (2007).

52.T. Manabe, K. Sonoyama, Y. Takanishi, K. Ishikawa, and H. Takezoe, “Toward practical application of cholesteric liquid crystals to tunable lasers, Journal of Materials Chemistry 18, 3040 (2008).