應用雷射繞射儀從事光學折射率與粒子直徑之量測

Abstract

本研究依據雷射繞射原理，將光柵所產生的繞射光沿著入射光路反射回去，經接收器量取繞射角度，配合光柵柵距與光源波長，經過計算公式而獲得浸潤介質折射率。實驗理論結合了Littrow 架構、光柵線距量測與浸潤式折射等量測技術，計算出浸潤液體之折射率。實驗中以線距833 nm 的光柵線距標準片，配合光學繞射技術求出純水、浸潤油等透明液體，與參雜微粒的半透明水溶液之折射率。結果成功驗證系統的可行性，並凸顯本研究實驗架構簡易、具有良好的重複性與準確性等優點。本文並且根據實驗的數據，解釋溶液中不同的溶質狀態與溶液折射率變化之關係。 除了線距量測以外，雷射繞射術還可量測某些微小物體的尺寸。所以本研究更提出了量測粉末粒子直徑的新方法。將雷射打在試片上的粉末產生繞射效應，再利用鏡組使同一階數的繞射光束匯聚成光點，透過量測光點偏移的角度，便可以計算出粒子直徑。之後再使用追溯式原子力顯微鏡，來量測表面粒徑做比對。由於兩者量測系統都基於不同的原理與計量特性，量測數值大致符合，結果也成功地證明了兩者的數據可以相互驗證。

This research presents a new measurement method for refractive index based on a laser diffractometer, in which a reflective diffraction beam coincides with an incident beam. With the angle of a reentry beam, grating pitch, and laser wavelength, we can calculate the refractive index. This study proposes a new method combined with the Littrow configuration, grating pitch measurement, and immersion diffractometry. This study uses the standard grating of pitch 833 nm with the method mentioned above to determine the refractive index of transparent liquids such as water, oil, and translucent liquids mixed with particles. Experimental data is used to explain variation in solution composition and the refractive index. In addition to measurement of refractive index, laser diffractometry can also be used to measure dimension of small objects. Therefore, this study also presents a new method for measuring nanoparticle diameter. A laser beam incident on the nanoparticle specimen produces diffraction effects. A lens focuses diffraction beams of the same order into a point. According to measured offset angle of the point, the particle diameter is calculated. To validate measurement results, a traceable atomic force microscope is also used to measure the surface properties of particle. Although both measurement systems are based on different principles and physical characteristics, the comparison of both measured results validate the proposed method.