光彈調變式偏光儀對線偏及圓偏的量測

Abstract

我們將偏光量測儀之補波片換成光彈調變器( PEM )以便發展成即時量測系統。本論文的貢獻有三點：首先是 Mueller矩陣光學的推導，以解釋如何量出圓偏吸收特性( CD )、線偏吸收特性( LD )、旋光特性( CB )及雙折射特性( LB )；其次是校正PEM的誤差後，量測出不同待測物的LD、LB、CD、CB值，並與理論模型做一個詳盡的探討；最後，將量測技術用在市售的圓偏極片及扭轉向列型液晶，證明了市售的圓偏極片雖然能產生等效的圓偏極光，但不具有圓偏吸收特性，至於扭轉向列型液晶，則驗證理論的架構，並成功的推算出扭轉角度( Twist Angle )及相位延遲( Phase Retardation )。

We will introduce the polarimetry system in our laboratory. For in-situ / real-time measurements, we replace the retarder in the system by a photoelastic modulator. The Mueller matrix of each optical element will be derived in this report. We will explain how to measure the CD (Circular Dichroism), LD (Linear Dichroism), CB (Circular Birefringence) and LB (Linear Birefringence). In addition to the theoretical derivation, we will calibrate the PEM of our laboratory and compare our limitation to that of commercially available systems. We will discuss some interesting results of TN-LC (Twist Nematic-Liquid Crystal). To our surprise, the measurement of a man made circular polarizer (CPL) behaves as a linear polarizer. After detail analyzing the property, we proved that the CPL contains only linear properties. In this report, we will discuss the effect of the residue static strain birefringence of a PEM, and explain its contribution to the signal. By measuring the solution of copper gluconate (a pure CD) and comparing with the CPL, we will discuss their difference in the report. By measuring NaK-d-tartrate in NiSO4, we find its CD value is almost proportional to the concentration of NaK-d-tartrate. In regarding the measurement of TN-LC, we not only derive the matrix of TN-LC but also match the experimental results with the modal. In this work, we shall prove that we can measure the phase retardation of a TN-LC and precisely measure its thickness. In a word, we actively develop the measuring skill for linear and circular anisotropic property and hope to enter the field of biochemistry, which is in rapid changing.