High precision Refractive-index Measurement Using Rainbow Method and Its Application to Water Analysis

在物质分析和河流、海水环境污染监测中，都需要一种简单、高精度的液体折射率测量方法。我们发展了一种测量液体折射率的新方法，该方法利用激光在装有液体样品的圆柱形容器中的最小偏差。这种方法的原理与自然彩虹的产生原理几乎相同，因此我们称这种方法为“彩虹方法”。被测液体装在直径60 mm的圆柱形玻璃池中，He-Ne激光入射到池中，使激光入射满足最小偏差条件。在这种情况下，从小室出射的光束有一个干涉条纹，可以作为测量激光光束微弱偏转的标志。基于惠更斯-菲涅耳原理，对该光学系统进行了计算机模拟。计算得到的条纹形状和条纹间距与实验结果吻合较好。结果表明，通过计算机模拟研究，可以确定含有样品的圆柱体直径与激光器光束大小的合适组合。利用每条条纹的偏差角-折射率特性曲线，经统计处理，实现了高精度的测量。并将其应用于水的分析，取得了较好的结果。

A simple and high precision method to measure the refractivity of a liquid has been required for material analysis and also for application to environmental pollution monitoring of river water and sea water. We have developed a new method for measuring the refractive indices of liquids, This method uses the minimum deviation of a laser beam in a cylindrical cell that contains the liquid sample. The principle is nearly the same as that of the generation of a natural rainbow, and we therefore call this method the "Rainbow Method". The liquid to be measured is contained in 60 mm diameter, cylindrical glass cell, and a He-Ne laser light is passed into the cell so that the laser light incidence fulfils the condition of minimum deviation. In this condition, the beam emerging from the cell has a interference fringe which can be used as a marker to measure the faint deflection of the laser beam. Based on Huygense-Fresnel principle a computer simulation was made on the optical system. The fringe shape and the fringe intervals computed are precisely coincident with those obtained in experiments. As a result, suitable combination on the diameter of the cylinder containing a sample and the beam size of a laser can be determined by the computer simulation study. By using the characteristic curve of deviation angle vs. refractive index for each fringe, and by the statistical treatment, measurement with high precision was demonstrated. Some application to the water analysis also has been carried out with fairly good result.