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研究生：	葉蕙溱 Yeh, Hui-Chen
論文名稱：	光場對摻雜偶氮染料膽固醇液晶結構之影響與其在可調控光子元件之應用 Effects of Light on Structures of Dye-doped Cholesteric Liquid Crystals and Their Applications in Controllable Photonic Elements
指導教授：	傅永貴 Fuh, Ying-Guey Andy 李佳榮 Lee, Chia-Rong
學位類別：	博士 Doctor
系所名稱：	理學院 - 光電科學與工程研究所 Institute of Electro-Optical Science and Engineering
論文出版年：	2008
畢業學年度：	96
語文別：	英文
論文頁數：	107
中文關鍵詞：	雙光子效應、全像光柵、光異構化、偶氮染料、液晶、空間濾波器
外文關鍵詞：	spatial filter, bi-photonic effect, liquid crystal, azo-dye, photoisomerization, holographic grating
相關次數：	點閱：95 下載：7
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染料摻雜液晶由於具有相當大的雙折射性，而且可經由液晶與受激染料分子間之交互作用而調控其光學特性，在全光控裝置的發展中多年來一直受到相當大的矚目。ㄧ般來說，偶氮染料分子在暗態時的穩定結構為trans態，然而，在適當短波長的光(一般在綠光或紫外光波段)激發下，染料分子的結構會轉變為cis態，同時會引致液晶結構產生改變，若同時以較長波長的光照時，cis異構物將快速轉變回trans的結構，使得液晶的結構維持在原來狀態。這種偶氮染料結構上的改變過程稱為光異構化反應。
本論文包含三個部分，簡要描述如下:
(1)第一部分主題是在摻雜偶氮染料的膽固醇液晶薄膜中，利用綠光激發後，使得液晶薄膜產生二維光柵結構。由於綠光引致染料產生trans-cis同分異構化反應，以及此過程中伴隨的熱效應，使膽固醇液晶的螺距變長。當綠光關掉後，薄膜中會立刻產生二維光柵的液晶結構。此光柵之產生起源於螺距縮短的過程中，由於彈性恢復力作用下所產生的不穩定現象。當綠光強度增加時，此二維光柵結構可維持較久時間，當以強的紅光照射時，二維光柵會較快消失。並且，光柵的間距與樣品螺距大小和光強度皆有關係。
(2)第二部分主題為以摻雜偶氮染料之膽固醇液晶薄膜作成可光控制之雙光子光柵元件。在此研究中，我們利用摻雜偶氮染料之膽固醇液晶，利用雙光子效應，作成可光調控光柵。主要地，在兩束相干之線偏振紅光重疊產生的干涉場中，利用圓偏振綠光的照射與否，可控制光柵的開或關。此雙光子光柵產生的機制是：在紅光干涉場光弱區，綠光激發下，染料分子產生由trans轉為cis的同分異構化反應，引致染料分子轉向光前進的方向，在紅光干涉場光弱區，紅光激發下則引致染料分子快速由cis轉回trans的同分異構化反應，此時會抑制染料分子轉向。因此最後，在紅光干涉場光弱與光強區的結構在空間中分別有類垂直與類平面螺旋之週期性分佈，雙光子光柵因而產生。
(3)第三部分主題是以摻雜偶氮染料之膽固醇液晶薄膜作成可光調控之半反半穿空間濾波器。此可光控空間濾波器的產生機制歸因於利用光致同分異構化反應調控膽固醇液晶之反射頻譜紅位移程度。以不同的入射光強度，經過物產生的不同繞射圖樣可被選擇性地穿透或反射，而得到high或notch-pass的穿透影像，以及相對應的low或band-pass的反射影像。此外，以傅利葉分析模擬和實驗的結果相當吻合。

Azo-dye-doped liquid crystals (LCs) have received considerable interest in the development of all optically controllable devices due to the LCs’ large birefringence and the ability to be flexibly controlled through interaction with the photo-excited azo-dyes. The azo molecules are generally stable in trans-state in dark and tend to change structurally to cis-isomers under the stimulus of light with an appropriate short wavelength (generally in green or UV region), resulting in a significant change of the structure of the LCs. The cis-isomers may cis-trans back-isomerize to the trans-state under the irradiation of light with a long wavelength such that the LC structure keep in the original state. The transformations of the azo dyes under illumination are called photoisomerization.
The thesis entitled “Effects of light on structures of dye-doped cholesteric liquid crystals and their applications in controllable photonic elements” includes three works. These works are briefly described as follows:
(1) The topic of the first work is “Photo-induced two-dimensional gratings based on dye-doped cholesteric liquid crystal films.” This work elucidates photoinduced two-dimensional (2D) gratings in dye-doped cholesteric liquid crystal films. The helical pitch is increased by green-beam-induced trans-cis isomerization and a concomitant thermal effect. Two-dimensional gratings appear when the green beam is turned off. Grating formation results from elastic instability caused by restored strain arising from helical pitch reduction. Grating lifetime increases as green beam intensity increases and declines under irradiation with a strong red beam. Variation in grating spacing with green intensity with various pitches is also examined.
(2) The topic of the second work is “Optically switchable biphotonic gratings based on dye-doped cholesteric liquid crystal films.” This study elucidates optically switchable gratings based on biphotonic effect in dye-doped cholesteric liquid crystal films. When one circularly polarized green beam is switched on (off), the gratings can be turned on (off) by illumination with an interference field generated by two linearly-polarized red beams. The biphotonic gratings (BGs) are formed by two mechanisms — green-beam-induced dye-reorientation through trans-cis isomerization, and red-beam-induced suppression of dye-reorientation by cis-trans back-isomerization. These mechanisms result in a spatially periodic distribution with homeotropic-like and planar-like structures, respectively, in dark and bright regions of the interference field, generating the BGs.
(3) The topic of the third work is “Optically-controllable transflective spatial filter with high- and low-pass or notch- and band-pass functions based on a dye-doped cholesteric liquid crystal film”. This study developed an optically-controllable transflective spatial filter in a dye-doped cholesteric liquid crystal (DDCLC) film. The mechanism of the optical tunability of the spatial filter is attributable to the photoisomerization-induced controllability of the red-shift of the reflection band in the DDCLC cell. At various intensities of incident beam, different spatial distributions of diffraction pattern via the object can be selected to be filtered, such that various high- (low-) pass, or notch- (band-) pass transmitted (reflected) images through the optical Fourier transformation processing can be obtained. A simulation based on Fourier analysis was developed, and it was highly consistent with experimental results.

Abstract................................................................................................I
Acknowledgements.......................................................................................VI
Contents..............................................................................................VII
List of Figures........................................................................................XI
List of Tables........................................................................................XVI

Chapter 1  Introduction.................................................................................1

Chapter 2  Properties of Liquid Crystals................................................................3
        2.1  Liquid Crystal Phases......................................................................3
2  Classification of Liquid Crystals..........................................................3
2.1  Lyotropic Liquid Crystals................................................................3
2.2  Thermotropic Liquid Crystals.............................................................4
3  Anisotropic Physical Properties of Liquid Crystals.........................................7
3.1  Birefringence............................................................................7
3.2  Electric Field Effects in an Insulating Nematic.........................................10
4  Elastic Continuum Theory of Liquid Crystals...............................................11

Chapter 3  Optical Properties of Cholesteric Liquid Crystals...........................................13
1  Introduction to Cholesteric Liquid Crystals...............................................13
2  Optics in Cholesteric Liquid Crystals by the Berreman’s 4×4 Matrix Method................15
2.1  Derivation of Matrix Wave Equations.............................................15
2.2  Dispersion Relation.............................................................20
2.3 Reflectance and Transmittance in Finite Slabs Between Isotropic Media............21
2.4  Distorted Helical Structures....................................................24
3  Optical Properties of an Ideal Helical Structure..........................................25
3.1  Dispersion Relation.............................................................26
3.2  Bragg Reflections...............................................................27
3.3  Waveguiding Effect..............................................................29
3.4  Optical Rotatory Power..........................................................30
4  Agents Influencing the Pitch..............................................................31
4.1  Temperature.....................................................................31
4.2  Concentration of the Chiral Dopant..............................................31
4.3  External Fields.................................................................32

Chapter 4  Effects of Light on Molecular Orientation of Liquid Crystals................................34
1  Direct Optical Torque in Nematics.........................................................34
1.1  Optical Nonlinearities of Nematic Liquid Crystals...............................34
1.2  Optical Fredericksz Transition..................................................38
2  Dye-Induced Torque in Dye-Doped Nematics..................................................39
2.1  Janossy Effect..................................................................39
2.2  Gibbons Model...................................................................41
3  Photoisomerization........................................................................41
4  Adsorption Effect.........................................................................44
5  Biphotonic Effect.........................................................................44

Chapter 5  Holographic Gratings........................................................................46
1  Laser-Induced Grating by Two Coherent Plane Waves.........................................46
2  Classification of Gratings................................................................52
2.1  Amplitude and Phase Gratings....................................................52
2.2  Thin (plane) and thick (volume) gratings........................................53
2.3  Volume reflection and volume transmission gratings..............................55
3  Diffraction Theory in Thin Transmission Gratings..........................................55
3.1  Scalar Diffraction Theory in Thin Transmission Gratings.........................56
3.2 	Vectorial Diffraction Theory in Thin Transmission Gratings.....................58

Chapter 6  Spatial Filtering...........................................................................59
1  Fourier Analysis..........................................................................59
2  Fourier Methods in Diffraction Theory.....................................................62
3  Spatial Filtering.........................................................................63
3.1  Spatial Frequencies.............................................................63
3.2  Abbe’s Theory of Image Formation...............................................65
3.3  Spatial Filtering...............................................................65

Chapter 7  Photoinduced Two-dimensional Gratings Based on Dye-doped Cholesteric Liquid Crystal Films...69
1  Introduction..............................................................................69
2  Experiments...............................................................................70
2.1  Experimental Preparation........................................................70
2.2  Experimental Setup..............................................................73
3  Results and Discussion....................................................................74

Chapter 8  Optically Switchable Biphotonic Gratings Based on Dye-doped Cholesteric Liquid Crystal Films
1  Introduction..............................................................................80
2  Experiments...............................................................................81
2.1  Experimental Preparation........................................................81
2.2  Experimental Setup..............................................................82
3  Results and Discussion....................................................................83

Chapter 9  Optically Controllable Transflective Spatial Filter with High- and Low-pass or Notch- and 
           Band-pass Functions Based on a Dye-doped Cholesteric Liquid Crystal Film....................90
1  Introduction..............................................................................90
2  Sample preparation........................................................................91
3  Results and Discussion....................................................................93
Chapter 10  Conclusion and Future works...............................................................103

References............................................................................................105
                                    

[1]P. G. de Gennes and J. Prost, The Physics of Liquid Crystals (Oxford University Press, New York, 1993).
[2]S. Chandrasekhar, Liquid Crystals (Cambridge University Press, 1992).
[3]I. C. Khoo, Liquid Crystals: Physical Properties and Nonlinear Optical Phenomena (John Wiley & Sons, New York, 1995).
[4]Pochi Yeh, and Claire Gu, Optics of Liquid Crystal Displays (John Wiley & Sons, New York, 1999).
[5]A. Yariv, Optical Electronics in Modern Communications (Oxford University Press, New York, 1997).
[6]W. Helfrich, Appl. Phys. Lett. 17, 531 (1970).
[7]W. Helfrich, J. Chem. Phys. 55, 839 (1971).
[8]R. C. Jones, J. Opt. Soc. Am. 31, 488 (1941).
[9]S. Teitler and B. W. Henvis, J. Opt. Soc. Am. 60, 830 (1970).
[10]D. W. Berreman, J. Opt. Soc. Am. 62, 502 (1972).
[11]C. W. Oseen, Trans. Faraday Soc. 29, 833 (1933).
[12]A. Sugita, H. Takezoe, Y. Ouchi, A. Fukuda, E. Kuze, and N. Goto, J. J. Appl. Phys. 21, 1543 (1982).
[13]A. Lien, Appl. Phys. Lett. 57, 2767 (1990).
[14]F. Simoni and O. Francescangeli, J. Phys: Condensed. Matter. 11, R439 (1999).
[15]M. Sheik, A. A. Said, T. H. Wei, D. J. Hagan, and E. W. Van Stryland, IEEE J. Quantum Electron. 26, 760 (1990)
[16]I. Jánossy and T. Kosa, Opt. Lett. 17, 1183 (1992); I. Jánossy, Phys, Rev. E 49, 2957 (1994); T. Kosa and I. Jánossy, Opt. Lett. 20, 1230 (1997).
[17]L. Marrucci, Mol. Cryst. Liq. Cryst. 321, 57 (1998).
[18]W. M. Gibbons, P. J. Shannon, S.-T. Sun, and B. J. Swetlin, Nature (London) 351, 49 (1991).
[19]Andy Y.-G. Fuh, C.-C. Liao, K.-C. Hsu, C.-L. Lu and C. -T. Tsai, Opt. Lett. 26, 1767 (2001).
[20]A. Y.-G. Fuh, C.-R. Lee and T.-S. Mo, J. Opt. Soc. Am. B 19, 2590 (2002).
[21]A. Y.-G. Fuh, C.-C. Liao, K.-C. Hsu and C.-L. Lu, Opt. Lett. 28, 1179 (2003).
[22]W. Urbach, H. Hervet and F. Rondelez, J. Chem. Phys. 83, 1877 (1985).
[23]H. J. Eichler, P. Günter and D. W. Pohl, Laser-Induced Dynamic Gratings (Springer-Verlag, Berlin, 1985) Chap. 2.
[24]P. Yeh, Introduction to Photorefractive Nonlinear Optics (John Wiley & Sons, New York, 1993).
[25]N. K. Viswanathan, S. Balasubramanian, L. Li, S. K. Tripathy and J. Kumar, Jpn. J. Appl. Phys. 38, 5928 (1999).
[26]E. Hecht, Optics (Addison Wesley, San Francisco, 2002).
[27]P. C. Mehta and V. V. Rampal, Lasers and Holography (World Scientific, Singapore, 1993) Chap. 4.
[28]P. Yeh, Introduction to Photorefractive Nonlinear Optics (John Wiley & Sons, New York, 1993).
[29]J. Tervo and J. Turunen, Opt. Lett. 25, 785 (2000).
[30]M. Kleman and O. D. Lavrentovich, Soft Matter: An Introduction (Springer, New York, 2003), p. 405.
[31]N. A. Clark and R. B. Meyer, Appl. Phys. Lett. 22, 493 (1973).
[32]M. Delaye, R. Ribotta, and G. Durand, Phys. Lett. 44A, 139 (1973).
[33]B. I. Senyuk, I. I. Smalyukh, and O. D. Lavrentovich, Opt. Lett. 30, 349 (2005).
[34]S.-W. Kang and L.-C. Chien, Appl. Phys. Lett. 90, 221110 (2007).
[35]J. P. Hurault, J. Chem. Phys. 59, 2068 (1973).
[36]T. Ishikawa and O. D. Lavrentovich, Phys. Rev. E 63, 030501(2001).
[37]W. Helfrich, Appl. Phys. Lett. 17, 531 (1970).
[38]W. Helfrich, J. Chem. Phys. 55, 839 (1971).
[39]H.-C. Yeh, G.-H. Chen, C.-R. Lee, and T.-S. Mo, Appl. Phys. Lett. 90, 261103 (2007).
[40]Y. Yu and T. Ikeda, J. Photochem. Photobiol. C 5, 247 (2004).
[41]H.-K. Lee, K. Doi, H. Harada, O. Tsutsumi, A. Kanazawa, T. Shiono, and T. Ikeda, J. Phys. Chem. B 104, 7023 (2000).
[42]H. Rau, Photochemistry and Photophysics (Chemical Rubber, Boca Raton, 1990), Vol. II, pp. 119-141.
[43]L. M. Blinov, Electro-Optical and Magneto-Optical Properties of Liquid Crystals (Wiley, Chichester, 1983), p. 225.
[44]W. M. Gibbons, P. J. Shannon, S. Sun, and B. J. Swetlin, Nature (London) 351, 49 (1991).
[45]H.-K. Lee, A. Kanazawa, T. Shiono, T. Ikeda, T. Fujisawa, M. Aizawa, and B. Lee, Chem. Mater. 10, 1402 (1998).
[46]M. Pei, Y.-J. Wang, and G. O. Carlisle, Opt. Eng. 40, 1481 (2001).
[47]U. Gubler, D. Wright, W. E. Moerner, and M. B. Klein, Opt. Lett. 27, 354 (2002).
[48]C.-R. Lee, T.-S. Mo, K.-T. Cheng, T.-L. Fu, and A. Y.-G. Fuh, Appl. Phys. Lett. 83, 4285 (2003), and reference therein.
[49]M.-R. Lee, J.-R. Wang, C.-R. Lee, and A. Y.-G. Fuh, Appl. Phys. Lett. 85, 5822 (2004).
[50]M. Y. Shih, A. Shishido, and I. C. Khoo, Opt. Lett. 26, 1140 (2001).
[51]T.-H. Lin and A. Y.-G. Fuh, Appl. Phys. Lett. 87, 011106 (2005).
[52]Y. Yu and T. Ikeda, J. Photochem. Photobiol. C 5, 247 (2004).
[53]H.-C. Yeh, G.-H. Chen, C.-R. Lee, and T.-S. Mo, J. Chem. Phys. 127, 141105 (2007).

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校外：2008-06-18公開

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