閃頻式影像偏光儀在生物上的應用

Abstract

閃頻式影像橢圓偏光儀已克服了 CCD 傳輸及儲存緩慢的缺點。 一般 CCD 至少須 0.03 秒方能取一組像，無法搭配 50KHz 光彈調變器信號的截取；利用短脈衝光源與 光彈調變器同頻率放射，即可凍結特定相位進而取像，再轉成物理參數即可形成影像 式橢圓偏光儀。 現以同樣的理念實施在Mueller 偏光儀上而形成 Mueller 影像偏光 儀 : 由偏光片及一1/4 補波片可產生四個偏極態，再由四個偵測偏極態來量測4μ4 Mueller matrix。 在 1996 年 Lu-Chipman 介紹了一種矩陣法，將Mueller matrix 分成 由散射所得的去極化的矩陣 (Depolarization matrix)、補波矩陣 (Retardation matrix) 及 衰遞矩陣 (Diattenuation Matrix)。 藉由此分解，我們可以研究材料的特性而無須受到 散射的影響，故可用以量測生物材料。 在這個研究中，我們也會採用誤差分析法去分 析本系統藉以了解偏光儀。 我們已具備建構偏光量測的完整技術:對準、校正及誤差 分析。

The stroboscopic illumination technique has been developed for imaging ellipsometry in a photoelastic modulated system to conquer the slow data transfer in CCD. The highest date rate for frame grabbing in CCD is 30/sec which is not comparable with the modulation frequency of photoelastic modulator (50Khz); we propose a short pulse illumination technique to lock the specific phase of the signal. Here, we like to propose the same technique to measure the 16 elements of Mueller matrix for materials. 4 polarization states can be generated by a polarizer and quarter wave plate, the output states of medium can be analyzed by 4 polarization states through a PEM and analyzer. The polar decomposition (Lu-Chipman decomposition technique) will be used to eliminate the depolarization of the scattering medium. According to Lu-Chipman technique (developed in 1996), one can decompose the Mueller matrix into Depolarization matrix, Retardation matrix and Diattenuation matrix. The retardation and diattenuation properties can be obtained without the depolarization of the optical system. In this work, the measurement errors of the instrument will be analyzed by equally weighted variance (EWV). We not only will calibrate the system by air, we will use it to measure the biological medium (such as leafs, tissues) to analyze its anisotropic properties. In this work, I will complete the necessary conditions for constructing an ellipsometry and polarimetry: alignment, calibration and error analysis.