基于全光谱拟合法的VO2薄膜光学常数计算

Optical Constants of VO_2 Thin Films Based on Whole Optical Spectrum Fitting

为实现对VO_2薄膜光学常数的测量,本文在全光谱拟合法的基础上,首先利用导纳矩阵法推导出透射率T与薄膜厚度d、折射率n以及消光系数k的函数关系,然后利用单纯形法得到其优化函数。最后采用Matlab编程方法对低温态、高温态VO_2薄膜的红外透射率进行了全光谱拟合,得到折射率和消光系数等VO_2薄膜光学常数的拟合曲线。结果表明:拟合曲线与已有研究结果及实测曲线基本吻合。采用全光谱拟合方法得到的光学常数能较准确的对VO_2薄膜进行描述,为最佳膜厚设计提供了依据。此外,为更简便地描述VO_2薄膜的光学常数,本文还引入了Cauchy色散模型方程,对全光谱拟合方法得到的中远红外波段(2.5~15mm)的光学常数结果进行了拟合。

In order to measure the optical constants of VO2 thin films, a whole optical spectrum fitting method is proposed in this paper. Firstly the admittance matrix method is used to derive the function of the transmittance ＂T＂, the film thickness ＂D＂, refraction rate ＂n＂ and extinction coefficient ＂K＂. Secondly, the simplex method is used to optimize this function. Finally, MATLAB programming method is used for whole optical spectrum fitting of infrared transmittance of VO2 thin films at low temperature and high temperature state. Then the fitting curves of the optical constants of VO2 thin films, such as refractive index and extinction coefficient, are obtained. The results show that the fitting curves are in agreement with the existing research results and the measured curves. The optical constants obtained by the whole spectrum fitting method can be used to describe the VO2 thin films accurately, providing the basis for the optimum design of film thickness. Furthermore, in order to describe the optical constants of VO2 thin films more easily, the Cauchy dispersion model equation is also introduced in this paper to fit the optical constants of mid far infrared wave band （2.5-15 μm） which was obtained by the whole spectrum fitting method.