在本論文中，我們藉由偵測摻雜偶氮染料液晶薄膜(DDLC)的動態光柵形成過程來探討染料分子受光後吸附在基板表面的動態現象，引致液晶定向排列效果。我們以兩道相干激發光束(氬離子雷射，波長514.5nm)在DDLC樣品上產生週期性干涉條紋，由偵測光(氦氖雷射，波長632.8nm)的一階繞射動態的強度變化，發現隨著激發光照射的時間增加，會造成液晶分子的重新排列；我們由實驗證實染料分子(Methyl Red)在干涉條紋光強處受光激發之後會逐漸吸附到樣品的玻璃基板內面，對液晶分子提供垂直激發光電場方向的負向力矩，並因染料吸附，在基板內面吸附區形成有如波紋的結構。由實驗量測結果發現，液晶分子會因染料吸附量之不同而影響液晶分子的排列方向，其中以兩主要因素主導液晶分子排列方向：(1)染料吸附提供一垂直激發光電場之負向力矩，導致液晶排列垂直激發光電場方向。(2)表面波紋造成的溝槽結構提供液晶一表面錨定力，導致液晶排列平行激發光電場方向。本實驗以氬離子雷射分兩道光，能量均為5mW照射樣品，以偵測光動態偵測一階繞射強度，發現在200秒前，因染料吸附提供液晶分子一垂直激發光電場之負向力矩，導致液晶排列傾向垂直激發光電場方向，而此時基板已有週期性波紋形成，但因溝槽深度尚淺，所以液晶排列方向由染料吸附對液晶之作用力所主導；在200~1300秒之間，由於溝槽深度因染料吸附而增深，提供液晶一表面錨定力大於染料吸附對液晶之作用力，導致液晶排列平行激發光電場方向；在1300秒之後，由於染料持續受光激發造成吸附，形成不規則枝條狀結構覆蓋在溝槽上，使溝槽對液晶排列之作用力減弱，取而代之的是染料吸附對液晶之作用力，導致液晶排列垂直激發光電場方向。我們可以藉由偏振激發光，控制液晶排列方向。

In this thesis, we study the dynamic behavior of the photoalignment effect on Dye Doped Liquid Crystal (DDLC) films. The two pump beams derived from an Argon ion laser (λ=514.5nm) set up a periodic interference of light on the DDLC sample, generating a phase grating. The dynamics of the first-order diffraction intensity of the probe beam (He-Ne laser,λ=632.8nm) are studied. Based on the obtained result, we confirm that the photoexcited Azo-dye molecules absorb onto the inner surface and induce a negative torque to reorient the liquid crystal molecules in the high-intensity regions of interference pattern. At the same time, we also observe the laser-induced ripple structure in the high-intensity regions of interference pattern. According to our experimental results, we conclude that there are two competing alignment torques to align the liquid crystals : (1) the Photo-excited dye molecules absorb on the substrates, and induced a negative torque to reorient the liquid crystal molecules in a direction perpendicular to the pump beam polarization , (2) the laser-induced surface ripple structure produce an azimuthal anchoring energy to reorient the liquid crystal molecules in a direction parallel to the pump beam polarization. The dynamics show three-stage results. When the power of each pump beam is 5mW, we observe that the photoexcited dye molecules absorb onto the inner surface and induce a negative torque to reorient the liquid crystal molecules in a direction perpendicular to the pump beam polarization in the first 200s. At the same time, we also observe the laser-induced ripple structure in the high-intensity regions of interference pattern. The amplitude of depth is low, so the azimuthal anchoring energy is week. During the period of 200-1300s, the ripple depth is high enough, so the ripple alignment torque is greater then the negative torque induced by the adsorbed dye molecules. As a result, the liquid crystals align along the ripple direction. Finally at times after 1300s, the adsorbed dyes form disorder net-work type structure over the ripple structure. The torque induced by the ripple on LCs becomes week again, so the negative torque is dominant in this stage, and aligns LCs in the direction perpendicular to the pump-beam’s polarization (which is parallel to the ripple direction). This interesting result allows us to control the alignment of liquid crystals in a cell, which is important for display application.

參考文獻
1. 松本正一、角田市良 合著 劉瑞祥 譯 液晶之基礎與應用 國立編譯館 台灣 (1996).
2. Hasegawa M and Taira Y, J.Photopoly. Sci. Technol. 8 241 (1995).
3. Lu J, Deshpande S V, Gulari E, Kanichi J and Warren W L, J. Appl. Phys. 80, 5028 (1996).
4. Dyadyusha A, Kozinkov V, Marusii T, Reznikov Y, Reshetnyak V and Khizhnyak A, Ukr. Fiz. Zh. 36, 1059 (1991).
5. Schadt M, Schmitt K, Kozinkov V and Chigrinov V G Jpn. J. Appl. Phys. 31, 2135 (1992).
6. Wayne M. Gibbons, Paul J. Shannon, Shao-Tang Sun, and Brian J. Swetlin, Nature 351, 49(1991).
7. W. M. Gibbons, T. Kosa, P. Palffy-Muhoray, P. J. Shannon ,and S. T. Sun, Nature 377, 43(1995).
8. I. Jánossy and A.D. Lloyd, Mol. Cryst. Liq. Cryst. 203, 74 (1991).
9. I. Jánossy and L. Csillag, Phys.Rev. A 44, 8410 (1991).
10. A. Y.-G. Fuh, C.-C. Liao, K.-C. Hsu, C.-L. Lu, T.-S. Mo “Laser-induced ripple structure of dopant on the substrates in a dye-doped liquid crystal cell and its alignment effect ’’ Journal of Nonlinear optical Physics and Materials (In press).
11. B. Bahoadur, Liquid Crystals-Applications and Uses, World Scientific Press, Singarpore(1990).
12. L. M. Blinov and V. G. Chigrinov, Electrooptic Effects in Liquid Crystal Materials, Springer-Verlag, New York(1994).
13. H. J. Eichler, P. Gunter, and D. W. Pohl, Laser-Induced Dynamic Gratings, Springer-Verlag Berlin Heidelberg (1986).
14. Robert W. Boyd, Nonlinear Optics, Academic Press, London (1992).
15. Pochi Yeh, Introduction to Photorefractive Nonlinear Optics, John Wiley ＆ Sons, Inc. New York, (1993).
16. T. V. Galstyan, B. Saad, M. M. Denariez-Roberge, J. Chem. Phys, 107, 9319(1997).
17. F. Simoni, O. Francescangeli, Y. Reznikov, S. Slussarenko, Opt. Lett, 22, 549(1997).
18. A. Y.-G. Fuh, C.-C. Liao, K.-C. Hsu, C.-L. Lu, and C.-Y. Tsai Opt. Lett, 26, 1767(2001).
19. Berreman D W ,Phys. Rev. Lett. 28, 1683 (1972).
20. R. W. Wood, Philos. Mag. 4, 396(1902).
21. Paul A. Temple and M. J. Soileau, IEEE J. Quantum Electronics 17, 2067(1981).
22. S. R. J. Brueck and D. J. Ehrlich, Phys. Rev. Lett. 48, 1678(1982).
23. H. M. Van Driel, J. E. Sipe, and Jeff F. Young, Phys. Rev. Lett. 49, 1955(1982).
24. Fritz Keilmann, Phys. Rev. Lett. 51, 2097(1983).
25. M. J. Soileau, IEEE J. Quantum Electronics 20, 464(1984).
26. R. J. Wilson and F. A. Houle, Phys. Rev. Lett. 55, 2184(1985).
27. Anthony E. Siegman, IEEE J. Quantum Electronics 22, 1384(1986).
28. S. E. Clark, N. C. Kerr, and D. C. Emmony, Appl. Phys. 22, 527 (1989).
29. W. Y. Y. Wong, T. M. Wong, and H. Hiraoka, Appl. Phys. A 65, 519 (1997).
30. T. V.Galstyan, B. Saad, M. M. Denariez-Roberge, J. Chem. Phys. 107, 9319 (1997).
31. A. G. Chen, D. J. Brady, Opt. Lett. 17, 441 (1992).
32. T. V.Galstyan, V. Drnoyan, S. M. Arakelian, Phys. Lett. A, 217, 52 (1996).
33. P. G. de Gennes and J. Prost, The Physics of Liquid Crystals,2nd ed, Clarendon Press, Oxford (1993).
34. I. C. Khoo, S. Slussarenko, B. D. Guenther, M. Y. Shih, P. Chen, W. V. Wood, Opt. Lett, 23, 253 (1998).