小尺度表面粗糙度与介质吸收对介质折射率测量的影响

将介质表面的小尺度粗糙度等效为覆盖在理想光滑表面上的多层等厚折射率渐变的薄膜,并通过特征矩阵计算多层等效膜模型的P光反射率与入射角的关系.将吸收介质的折射率虚部带入菲涅尔公式进行计算.运用COMSOL Mutiphysics软件对表面粗糙度和介质吸收进行建模和仿真计算.计算结果表明,小尺度表面粗糙度与介质吸收都会导致折射率测量产生误差.分别考虑以布儒斯特角和全反角作为折射率测量的手段,为了得到优于10-5的测量准确度,测量表面粗糙介质的折射率时,采用全反角进行判定;测量具有吸收效应的介质折射率时,采用布儒斯特角进行判定.

Effects of Small-scale Surface Roughness and Absorption on Refractive Index Measurement by the Brewster-angle and Critical-angle Techniques

Small-scale roughness on surface is equivalent to a multilayer structure with same thickness and gradient refractive index.By using characteristic matrixes, the reflectivity of P waves of the effective multilayer model with different incident angle is calculated;the refractive index of the absorbing medium is a complex number in the calculation of Fresnel formula;COMSOL Mutiphysics is used to model and simulat the small-scale roughness and absorption.The calculation results show that both the small-scale roughness and absorption of the dielectrics can make errors in measurement of the refractive index.In conclusion, in order to get the precision of 10-5 , the refractive index of rough dielectrics should be measured by critical-angle technique, while it is better to measure absorbing dielectrics by Brewster-angle technique.