Analysis On Effective Medium Approximation And Anisotropic Mueller Matrix In Ellipsometry Measurement Of Rough Surfaces

The study on radiation and polarization characteristic s of randomly rough surfaces has a wide application prospect in military and civillian fields,such as space remote sensing,infrared stealth and target tracking.It's important to obtain the optical constants and morphological parameters of randomly rough surfaces acccurately in micro-scale thermal radiation and optics.Now It's very popular to use spectroscopic ellipsometric(SE)method to measure and inverse the optical constants of meteria.The method depends on Fresnel formula of smooth surfaces.However,no matter how smoothly the sample polished,it can't be avoid the error in ellipsometry measurement because of roughness.In order to reduce the erro of ellipsometry measurement,researchers usually adopted effective medium approximation to model rough surfaces.But it's not so uniformly the rough surfaces distribute that the accuracy of effective medium approximation model depends on the morphology and optical constants of rough surfaces.The paper studied the regime map about rough surfaces' effective medium approximation model in ellipsometry measurement,so that the accuracy and application of effective medium approximation model can be explored.At present,atomic force microscope and scanning electron microscope are usually used to obtain the morphology of rough surfaces.But they may destruct on the surfaces and work slowly.The mueller matrix containing sixteen elements can adequately describe the optical information about anisotropic rough surfaces.Researching the influence of rough surfaces' morphology and optical constants on Mueller matrix,this paper tried to find a good method to inverse the optical constants and morphology of rough surfaces directly.This article adopted EMA to model Gaussian distributed randomly rough surfaces and used the rigorous coupled-wave analysis(RCWA)to solve the SE parameters of the EMA model.This paper adopted the finite-difference time-domain(FDTD)method to simulate the rough surfaces' electromagnetic response so that the SE can be obtained.The regime map of EMA models can be drew finally.The accuracy about EMA model is influenced not only by the morphology of rough surfaces but also by the category of metera.If using EMA to model the rough surfaces with high absorption,the precisions of amplitude ratio and extinction coefficient are higher while the precisions of phase difference and negative refractive index are influenced greatly by the morphology of rough surfaces.The rough surfaces with weak absorption have an opposite conclusion.By comparing different results,we find that the precision of negative refractive index depends on the phase difference while the precision of extinction coefficient is mainly affected by amplitude ratio of polarized light.In the paper,factors including the angle of incident light,the optical constants,the relative surface roughness and the correlation length are considered to study their effect on the Mueller matrix of rough surfaces.The conclusion is as follows.The values of deputy diagonal elements are more sensitive to the morphology of rough surfaces than main diagonal elements.While the values of main diagonal elements are larger than deputy diagonal elements.If the angle of incident light is not over sixty-five degrees,the element m12 of main diagonal lines is not changed While the elements m33 and m34 change linearly with rough surfaces' morphology.The slope of element m33 is influenced by extinction coefficient k while the slope of element m34 is independent of k.The value of deputy diagonal element m24 descends with the value of ?/? and is nearly not influenced by extinction coefficient k.This part is a key step to directly invert the morphology parameters and optical constants of anisotropic materials by Mueller matrix.