全像光栅在液晶及高分子材料的研究课件.ppt

Introduction 主要特徵： 1.分子長軸方向有序 2.重心位置無序 (director axis) 向列相(nematic)液晶分子的排列圖及方位秩序 S(θ) = 3cos2θ-1 精品文档 液晶的正單光軸晶體光學雙折射性 e n o n e n o n ) ( q eff n q ) ( q eff n q 精品文档 Dielectric anisotropy of the liquid crystals E LC Δε=ε∥-ε⊥ 若Δε0 uE minimum 若Δε0 uE minimum 精品文档 5CB液晶折射率隨溫度的變化 精品文档 5CB液晶方位秩序隨溫度的變化 精品文档 Dye-Induced Torque in Dye-Doped Nematics Janossy model (“Positive” torque ) Excited-state of dye molecules Ground-state of dye molecules n n 精品文档 Gibbons model (“Negative” torque) E 精品文档 Photoisomerization Effect Induced LC Reorientation Upon absorbing light, azo-dye molecules may undergo a photo-induced conformational change, which is called photoisomerization effect. 精品文档 Laser induced grating q l p I1 I2 L x I x z y q 1 k r 2 k r x z y q x z y q k r k r k r k r x z y q 精品文档 I1=I2=I0 Imax=4I0 Imin=0 The definition of the first order diffraction efficiency: Λ 精品文档 Experimental setup MIRROR He-Ne LASER MIRROR BEAM SPLITTER SAMPLE APERTURE FILTER DETECTOR OSCILLOSCOPE POLARIZER Nd: YAG LASER 精品文档 Results and discussion Experiment I-1: (Pump , Probe) A∥/A⊥=4.5 ( ⊥, ∥) (⊥, ⊥) (∥, ∥) (∥, ⊥) 精品文档 (⊥,∥) (Pump, Probe) 精品文档 31℃ 30.5℃ 30℃ 29.5℃ 31.5℃ 精品文档 (Pump, Probe) 精品文档 no ne nav nav ~ 0.112 ~ 0.058 29.5~31.0℃ n 31.5℃~32.5℃ 激發光源偏振垂直導軸 精品文档 nav nav 激發光源偏振平行導軸 n 精品文档 精品文档 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 精品文档 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 精品文档