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16 October 2010 Determination of the optical constants of thin films by means of transmission spectra and curve fitting
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A method to calculate the optical constants (refractive index n, film thickness d and extinction coefficient k) of double-coated thin film by use of transmission spectrum is described in this paper. For double-coated glass films, the relationship between T, λ, n, k and d is analyzed theoretically. Then the method to determine these optical parameters by curve fitting is introduced. Several samples with different Sn concentrations have been prepared. According to the method mentioned above, we calculate the coefficients of Sn-doped SiO2 films produced by Sol-gel method. Two kinds of expressions for the refractive index n are introduced. One is Cauthy model. The other is defined as Polynomial model. Also the expressions for k are given similarly. At last, the experimental curves are fitted according to the transmittance formula. Results show that the refractive index becomes larger with the increase of Sn in the compound. Also, it turns out that the refractive index decreases when the wavelength increases. This method combines the extreme point method with the whole transmission spectra fitting method. This can improve the fitting accuracy.
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Hongzhi Jia and Huancai Lu "Determination of the optical constants of thin films by means of transmission spectra and curve fitting", Proc. SPIE 7656, 5th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Optical Test and Measurement Technology and Equipment, 76565G (16 October 2010);

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