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全像光柵在液晶及高分子材料的研究

全像光柵在液晶及高分子材料的研究. 黃宣瑜 國立中山大學物理系 非線性光學實驗室 奈米科技研發中心 博士後研究. Experiment. I : Temperature and polarization dependence of transient gratings in azo-dye- doped liquid crystals II : The enhancement of diffraction in liquid crystals on dye-doped polymer films. Introduction. 主要特徵：

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全像光柵在液晶及高分子材料的研究

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  1. 全像光柵在液晶及高分子材料的研究 黃宣瑜 國立中山大學物理系 非線性光學實驗室 奈米科技研發中心 博士後研究

  2. Experiment I: Temperature and polarization dependence of transient gratings in azo-dye- doped liquid crystals II: The enhancement of diffraction in liquid crystals on dye-doped polymer films

  3. Introduction 主要特徵： 1.分子長軸方向有序 2.重心位置無序 (director axis) S(θ) = <3cos2θ-1> 向列相(nematic)液晶分子的排列圖及方位秩序

  4. n n o o n n e e q q n n ( ( ) ) eff eff q q 液晶的正單光軸晶體光學雙折射性

  5. 若Δε>0 uE minimum 若Δε<0 uE minimum Dielectric anisotropy of the liquid crystals E Δε=ε∥-ε⊥ LC

  6. 5CB液晶折射率隨溫度的變化

  7. 5CB液晶方位秩序隨溫度的變化

  8. Dye-Induced Torque in Dye-Doped NematicsJanossy model (“Positive” torque) n Ground-state of dye molecules Excited-state of dye molecules n

  9. Gibbons model (“Negative” torque) E

  10. Photoisomerization Effect Induced LC Reorientation Upon absorbing light, azo-dye molecules may undergo a photo-inducedconformationalchange, which is called photoisomerization effect.

  11. l p x I1 x x x x q r r r k k k L 2 I2 q q q q z z z z I y y y y r r r k k k 1 Laser induced grating

  12. Imax=4I0 Imin=0 I1=I2=I0 Λ The definition of the first order diffraction efficiency:

  13. Experimental setup OSCILLOSCOPE MIRROR Nd: YAGLASER DETECTOR APERTURE BEAM SPLITTER POLARIZER FILTER He-Ne LASER MIRROR SAMPLE

  14. Results and discussion Experiment I-1: A∥/A⊥=4.5 (Pump , Probe) ( ⊥, ∥) (⊥, ⊥) (∥, ∥) (∥, ⊥)

  15. (Pump, Probe) (⊥,∥)

  16. 31℃ 31.5℃ 30.5℃ 30℃ 29.5℃

  17. (Pump, Probe)

  18. no nav ne nav 激發光源偏振垂直導軸 n 29.5~31.0℃ ~ 0.112 ~ 0.058 31.5℃~32.5℃

  19. nav nav 激發光源偏振平行導軸 n

  20. Conclusions of Experiment Ⅰ-1 1.產生瞬態光柵的機制有兩個。 2.寫入光的偏振平行於導軸時的一階繞射訊號較大。 3. 一階繞射訊號衰減時間會隨溫度的上升而增加。

  21. Experiment II: The enhancement of diffraction in liquid crystals on dye-doped polymer films

  22. DR1-PMMA薄膜在不同的pulse energy作用下之一階繞射效率

  23. 36℃ 34℃ 32℃ 27℃

  24. DDPF 及DDPF/5CB 薄膜的SRG DDPF DDPF/5CB

  25. Conclusions of Experiment II: 1. 寫入光源能量足夠大時(4.5mJ/cm2)，作用於DR1- PMMA薄膜產生的繞射訊號沒有鬆弛現象。 2. 訊號凹陷(dip) 是由於光散射的結果。 3. DR1-PMMA/5CB樣品所產生的表面起伏光柵(SRG)較深。

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