雷射光場導致液晶分子偏轉在鄰近相變點溫度時其非線性效應之研究

Study of strong self-focusing and -defocusing effects with bulk liquid crystal films at temperature near clearing point

張任遠(Jcn-Yuan Chang)

指導教授 ： 蔡明善

中原大學/理學院/應用物理研究所/碩士(2002年)

https://doi.org/10.6840/cycu200200107

摘要

在本論文中所做的研究中主要是探討液晶在偏極光的照射下光場拉扯液晶分子的現象，由於液晶分子的偏轉，使得折射率會形成非線性的分佈，並造成自聚焦的效應，在這裡我們使用的液晶是5CB，並且將液晶加溫，觀察液晶在不同溫度對偏極光照射時所發生的變化，在加溫後由光學顯微鏡所觀測到的實驗結果可以看到明顯的自聚焦效應，再用聚光干涉(Conoscope)的方法觀察液晶，從實驗結果中可以看到橢圓形的圖樣，認為這是液晶的缺陷結構，接下來將液晶加溫至接近相變溫度，再用聚光干涉的方法觀察液晶樣品，從實驗結果中可以看到偏極光影響液晶分子偏轉的距離延長了，溫度上升的確可以輔助偏極光在液晶中的自聚焦現象，最後再以氦氖雷射作為偵測光觀察液晶分子偏轉的變化，由實驗結果可知偵測光被偏轉的液晶所影響而分成兩道光，這與之前的理論相符合，即偵測光源經過缺陷結構時所造成的結果。

關鍵字

液晶 ； 自聚焦 ； 缺陷結構

並列摘要

The purposes of these experiments mainly studied the nonlinear effects of laser induced liquid crystal reorientation at temperature near clearing point. Strong self-focusing and-defocusing effects were observed through optical microscope when laser beam was incident into the bulk liquid crystal film. The self-focusing effect was due to optical Kerr effect. The polarization of laser field induced the liquid the crystal orientation and aligned the director of liquid crystal at the same direction. This resulted the liquid crystal cell is similar to a Grin lens, so the laser beam can be focused. The self-defocusing effect was an interesting phenomenon. By conoscopic technique, a concentrate ring pattern was observed at the image plane. It was considered the bulk liquid crystal film was unstable and it can form point defects with a strong laser beam incident the bulk liquid crystal films intensity. The laser beam could not propagate through the point defect and would result the laser beam spited into two beams, so the self-defocusing effect was generated. The pump-probe technique also sustained our point of view.

並列關鍵字

defect ； self-focusing ； liquid crystals

參考文獻

2. E.Lueder ,Liquid Crystal Displays (John Wiley , 2001).

3. R.M. Herman and J.R. Serinko, Phys. Rev. A .19 , 1757 (1979).

6. S.Elston and R.Sambles, The Optics of Thermotropic Liquid Crystal (Taylor & Francis , 1998).

7. F. Simoni ,Nonlinear Optical Properties of Liquid Crystals and Polymer Dispersed Liquid Crystals (Word Scientific , 1997)

8. G. R.Fowles,Induction to Modern Optics , second edition (Holt , New York , 1975)