光彈調變式橢圓偏光儀對各向異性材料的動態量測

Abstract

此研究的目的為發展一套快速且準確的光彈調變式橢圓偏光儀量測系統，藉由波形分析法及基因演算法，可量測異向性材料的光學參數，包括三個主光軸折射率及歐拉角 (Euler angle)，時間解析度可達 20 μs。在分析樣品反射光強度波形的過程中，我們得到折射率的參數方程式，可用來縮減參數於數值計算中的求解範圍，提高收斂效率。此外，我們也歸納出在反射式架構下量測異向性材料時，以雙光量測，即入射角為 65 及 70° 的系統。此系統可同時滿足架構的簡易性又可快速量測出準確的光學參數。對於光軸在任意方向的單光軸材料，此系統在反射式架構下量測折射率的準確度可達 10-3，而在穿透式架構下，結合了傅利葉技術及波形分析技術，量測塊狀材料 (厚度約 2 mm) 折射率的準確度可優於 10-6。論文中除了發展此套量測系統，更將此系統應用於量測三種光折變全像材料，從折射率的動態變化中，我們可以進一步了解材料的反應機制。

In this research, we have developed a fast and accurate phase modulated ellipsometry/polarimetry. The optical parameters, the refractive indices and the Euler angles of three principal axes can all be extracted from the intensity waveform within one cycle of modulation (20 μs) through the genetic algorithm. By analyzing the reflected intensity waveforms, we can obtain a set of parametric equations for providing the appropriate boundaries of refractive indices in the numerical procedure. We also found that the two-probe-beam configuration is the optimized configuration for measuring the optical parameters of a uniaxial medium. We suggest 65 and 70° to be the incident angles in ellipsometry, the optimal configuration will be analyzed by the variation of intensity with respect to the optical parameters. For an arbitrarily orientated uniaxial medium, the refractive indices can be accurately obtained with a precision of 10-3 by ellipsometry. For the transparent material with weak anisotropy, one can employ the polarimetry to enhance the resolution of refractive index. By combining the waveform extraction and Fourier transform techniques, the precision of the refractive index of a thick medium (~ 2 mm) has been reached to 10-6. We have applied these techniques for measuring three different photo-refractive materials. Therefore, one can measure the dynamic optical parameters of material under some temporal phasical change.