橢圓偏光光譜儀對線性二色及雙折射複合式結構之研究

Abstract

利用光彈調變式橢圓儀量測具有複合式結構的材料。在本論文中選用了商業圓偏光片為樣品，圓偏光片是由具雙折射的1/4λ補波片及線性偏極片兩種材料組成。 本研究將以 Kr-Ar可調波長雷射為量測光源，建立一複合式結構材料在各波長的特性的量測技術。 首先建立數學理論式並與實驗圖形做比對，藉以粗略判斷材料的吸收軸和快軸的軸向。接著再將不同析光片方位角下的一倍頻和二倍頻訊號，藉由數值擬合的方法，進一步求得圓偏片參數: 線性偏振二向性(Linear Dichroism, LD)、雙折射(Linear Birefringence, LB)及LD的穿透軸與LB的快軸之間的夾角(γ)。雖然量測到的γ為一定值，但並非理論上的45∘，而LD和LB在不同波長下也幾乎維持定值。 最後，我們移除架構中起偏片和光彈調變器，並旋轉析光片量測樣品的出射光強度，驗証實驗所得結果的可靠度。

The Photoelastic Modulation Ellipsometer is used to measure an artificial circular polarizer (CP), which is a combination of a linear polarizer and a retarder. The multi-wavelength measurement technique is built up by using the Kr-Ar tunable laser. In the beginning, the azimuth direction of optical axis of this CP is roughly determined by comparing the theoretical model with its measurement for a single wavelength. The parameters: linear dichroism (LD), phase retardation and the azimuth angle between the linear polarizer and retarder (γ) are measured by fitting its 1st and 2nd harmonics signals of various azimuth positions of analyzer for the Kr-Ar tunable laser. Although the measured □ is independent of wavelength but it is not at 45o, and its phase retardation and LD are almost the same for every wavelength. Finally by comparing the theoretical transmission, which is derived by substituting its measured parameters, to its measured transmission under various azimuth positions of analyzer, we observed a well fitted result for every wavelength.