DETERMINATION OF THE COMPLEX INDEXES OF REFRACTION OF GLASSES USING KRAMERS-KRONIG TRANSFORMATION

The radiative heat transfer in a mineral wool insulation is dependent on the complex index of refraction of the mineral raw material. The direct measurement of the index of refraction in the infrared range is difficult because the glasses are non-transparent, especially if the iron content is high. The determination of the index of refraction in the wavelength range 400-4000 cm-1 has been performed by measuring the specular reflectance in this range and then calculating the refractive index with Kramers-Kronig dispersion analysis. The computer program that performs the analysis directly from the measured infrared spectrum has been developed in order to minimize the calculation uncertainties. The accuracy of the calculation is checked against known data. The infrared spectra of seven different glasses have been measured and their indices of refraction determined.