光彈調變式橢圓偏光儀對扭轉式液晶的研究

Abstract

利用光彈調變式橢圓偏光儀在不須轉動任何元件的情況下，量測扭轉式液晶 (TN-LC) 的光學參數，如扭轉角及相位延遲。經校正液晶第一層的錨定方位角後，本系統可以即時量測橢圓偏光參數 psi 和delta。為了瞭解 TN-LC的異向特性 (anisotropic properties)，我們轉動液晶樣本，由於觀察到 psi 和delta 在各角度分佈圖形並不對稱，故可推斷液晶應同時具有線性及圓的異向特性 (即LB、CB 及LD、CD) 。將 TN-LC所量出的光學參數轉換成橢圓偏光參數，其結果與實驗量測值相當吻合。由於可以即時量測橢圓偏光參數，故可以研究TN-LC在不同電壓下的動態反應；由 psi 和delta 所推出的穿透率可求出 TN-LC的反應時間。最後，我們並將所量得的 psi 和delta 轉成偏振態 (Stokes Parameters) 同時繪出在邦加球 (Poincare Sphere) 上的改變軌跡。

We can measure the twist nematic liquid crystal (TN-LC) parameters, such as twist angle and phase retardation by the photoelestic modulated ellipsometry without rotating any component in the system. After adjusting the rubbing direction of TN-LC, we can measure the ellipsometric parameters psi and delta in real time. For understanding the anisotropic properties of TN-LC, we rotated TN-LC and observe the unsymmetrical phenomenon in psi and delta . By careful analyzing the model, we can judge that TN-LC contains both linear and circular anisotropic properties. We also transform the measured TN-LC parameters into its corresponding ellipsometric parameters, which consist with our ellipsometric measured values. Because of the real time measurements, we can study the dynamic phenomenon of TN-LC under applied voltage; we further derive the transmission from psi、delta , and measure the response time of TN-LC. In this study, we proved that the response time is longer in low applied voltage than it is in higher applied voltage. Finally we transform psi and delta into Stokes Parameters, and trace out its polarization state on Poincare Sphere.