光彈調變系統中的角度及其應用

Abstract

為了取代量取最小光強度之歸零式技術，本論文提出高光強度比例技術，以作為光彈調變量測系統中光學元件方 位角校正方法。在光彈調變量測系統中，當析光片在特定偏光角時其直流光強度在零階貝塞函數零點附近為線性 。透過光彈調變器中峰值相位調變振幅的改變，在兩固定向位差角之析光片，其直流光強度斜率比值可直接量測 光彈調變器與析光片穿透軸之間的相對向位角。利用類似的方法，我們也可精確的校準波片的光軸位置及反射面 。將析光片方位角設定在90°位置，直流光強度之斜率亦可量得石英1/4波片的橢圓傾角及BSO相位片的旋光度。 石英補波片中多重反射會放大橢圓傾角，故除了直射外我們也量了斜射波片的橢圓傾角及相位延遲。將光彈調變 器視為一橢圓延遲片，當其內稟雙折射及橢圓率納入考慮更可提升量測精度。總結本論文所提出之量測技術，不 但對於量測系統光學元件及入射面具有精準的校正能力，亦可應用在線性雙折射同時具旋光度特性之材料的量測 上。

Instead of the nulling method, we propose a high-level intensity technique to determine the relative azimuth orientation of a photoelastic modulator and an analyzer. In a photoelastic modulating system, one can obtain a DC intensity distribution by varying the phase modulation amplitude at two azimuth angles of the analyzer, which are p/4 apart from each other. The relative azimuth orientation can be determined by taking the ratio of the slopes of these two intensity distributions around the linear region of the zero point of the zero-order Bessel function. A similar technique is also applicable to wave plates and reflecting surface for aligning their optical axes and the plane of incidence with respect to the system. Adjusting the analyzer at 900 to the strain axis of a photoelastic modulator, one can determine the optical activity by measuring the slope of its DC intensity distribution under various phase modulation amplitudes. This technique was applied to measure the ellipticity of few quartz quarter-wave plates and the optical rotation of an optical active crystal. A multiple reflection enhancement effect in the wave plate was observed and discussed. By considering the photoelastic modulator as an elliptical retarder, we also determined its intrinsic ellipticity and static phase retardation, to increase the accuracy of measurements. We conclude that this high-level intensity technique is capable to align the optical elements, and can be considered as an alternative method to measure the optical activity in crystals, in which optical activity and birefringence coexist.