使用外差干涉儀測量光學常數之研究

Abstract

利用外差干涉儀測量各種測試系統所引入直角正交偏光間相位差，並根據相位差變化量來進行待測物如折射率、消光係數及厚度等之光學常數的測量。 在測量薄膜的光學常數方面，提出一種正向入射的折射率計及斜入射反射式折射率計。其特點在於以固定入射角測量及透過旋轉檢偏板方位角的方式，求出待測物的未知參數，故較一般折射率計使用方便及快速測量。 在測量膜厚超過測試光波長的光學參數方面，提出一種結合旋光外差干涉術及雙波長外差干涉術的測量方法。它可以同時測量待測膜和基板的折射率及厚度並且可以避免厚膜所發生2□相位模糊的問題，可以精確且容易的求出厚膜的折射率及其厚度。 在單軸晶體的ne、no測量及光軸判定方面，依照經待測晶體反射光的正交偏光分量間的相位差變化，在加上適當的判斷條件，即可計算出折射率及判定其光軸的位置。 本論文所提出的方法除了具有外差干涉術高精確度、高穩定度的優點外，還具有下列幾項特點:(1)可將檢偏板方位角載入調制訊號的相位中，較線偏光外差干涉術多一個量測上的自由度；(2)可以固定入射角測量，免於重複校正光路，達到快速與即時測量的需求。

The phase differences between two orthogonal polarizations of the test reflected beams under different conditions are measured by using heterodyne interferometry. Based on them or their variations, the optical constants, such as refractive index, extinction coefficient, and thickness of the test media can be estimated. Firstly, two types of refractometers are proposed. One is of normal incidence type and the other one is oblique incidence type. Their phase differences are measured under their associated specified incidence angles and different the azimuth angles of the analyzer. To these two refractometers have easy operations and rapid measurements. Secondly, a method for measuring the optical constants of a thick film is proposed by combining circular heterodyne interferometry and two-wavelength interferometry. It can measure the optical constants of the thick film as well as these of the substrate simultaneously, without the phase wrapping ambiguities. Finally,a method for determining the optical axis and two measurement methods for determining ne, no of a uniaxial crystal is proposed. When the property of test crystal is unknown, some possible pairs of solutions for (ne, no) can be calculated based on the values of the phase differences under different incident angles. The corrected solution for (ne, no) can be obtained by justifying with physical conditions, and the associated axis can also be determined. When the property of test crystal is identified, we can measure the ne and no directly after the optic axis is determined. Because of their heterodyne interferometric phase measurements, thy have all advantages of heterodyne interferometry. Moreover, they have also easier operations by changing the azimuth angles of the analyzer instead of the incidence angles.