外差干涉術在量測s-與p-偏光間相位差變化的應用

Abstract

首先利用電光晶體調制雷射光，使之成為具有適當差頻的外差光源。接著以此外差光源量測各種系統所引入s- 與p- 偏光間的相位差變化，並根據相位差的變化來進行各種參數的量測。針對待測物的待測量，量測系統可分為共光程與不共光程干涉儀兩種。 在不共光程干涉儀的結構中，以可調波長二極體雷射為光源的外差干涉術來做干涉信號之中心條紋的定位。此方法除了可定出中心條紋的位置外，還可判斷干涉儀兩臂何者較長。 而在共光程干涉儀的結構中，探討量測折射率的方法；其中包括有全反射法、相位差之極大值求折射率法，以及根據全反射法所設計的液體折射率計。並發展出旋光外差干涉術，來量測材料的布魯斯特角，進而求得折射率。另外還有複數折射率的量測，以及磁頭滑片的等效複數折射率與其飛行高度的量測。這些應用都是以外差干涉術量出相位差，然後代入菲涅爾方程式解出待測的物理量。 本論文所提出的量測方法有光學結構簡單、操作容易、高穩定度與快速量測等優點。而由於外差干涉術可精確地量出相位差，因此量測解析度亦高，使其具有實用的價值。

A laser light is modulated by an electro-optic modulator to become a heterodyne light source with a suitable frequency difference. This heterodyne light source is used to detect the phase difference variation between the s- and p- polarization, when light transmits through or is reflected from a medium. From the analysis of the phase difference variation, some parameters of the medium can be obtained. Depending on the characteristics of the test medium, the optical configuration can be divided into two types: a common-path heterodyne interferometer and a non-common-path heterodyne interferometer. In the case of a non-common-path heterodyne interferometer, the laser is replaced by a tunable laser-diode. It can be used to identify the central fringe and is easy to judge which arm of the interferometer is longer. In the case of a common-path heterodyne interferometer, the measurement methods of the refractive index are investigated. They include the total-internal-reflection (TIR), the maximum phase difference of TIR, and liquid refractometer. Besides, The circular heterodyne interferometry is developed to determine the Brewster's angle. Moreover, the measurements of the complex refractive index, and the effective complex refractive index and the fly-height of the read-write head slider are introduced. In these methods, the phase difference is measured by the heterodyne interferometry firstly. Then it is substituted into Fresnel's equations, and the refractive index of the test medium is obtained. Because the heterodyne interferometry can determine the phase difference precisely, these methods have the high measurement accuracy. Besides, they have several merits such as simple optical setup, easy operation, and rapid measurement. Hence, it is suitable to applied these methods to industry.