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Different methods for determining the refractive index of SiO2 glass in the range 1.4-50 µm
Harald Mehling, Joachim Kuhn, Jochen Manara, Rainer Brandt, Jochen Fricke

The refractive index n – ik is the key optical property for calculating the radiative and combined radiative – conductive heat transfer in scattering as well as in nonscattering media. Both n and k can vary over several orders of magnitude in the important spectral range from the near to the mid infrared. Different methods to determine the refractive index on nonscattering samples with specular reflecting surfaces exist, but each of them is only applicable under limited conditions with respect to spectral range and sample thickness. In this work, these limitations are identified and discussed. Experimental and evaluation techniques are improved, where possible. The determination of the refractive index of SiO2 glass in the 1.4 to 50 μm range was performed as a case study. The resulting data for the refractive index determined by different methods in our laboratories are presented and compared with each other as well as with literature data. Excellent agreement between data from different methods is found in those spectral regions where these methods are applicable.

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