Identification of the spectral complex refractive index of pure silica micrometric fibers versus temperature

Abstract

A new methodology was developed to identify the spectral complex refractive index of semi-transparent solid phases within heterogeneous media up to high temperatures. In this methodology, numerical samples are first generated from statistical information about the microstructure of a given material obtained by X-ray micro-tomography. The radiative properties of these numerical samples (reflectance, transmittance, and emittance) are then simulated with a Geometric Monte Carlo Ray Tracing code while the radiative properties of the real material are measured by Fourier Transform Infrared spectroscopy. The spectral complex refractive index is then extracted thanks to an optimization algorithm, by minimizing the discrepancies between the experimental and numerical radiative properties. This methodology was applied to a fibrous sample made of pure silica. The complex index was extracted at 295 K and 1010 K. In both cases, it enabled a good prediction of the radiative properties of the material and proved the relevance of performing calculations with characteristics identified at the local scale instead of the bulk ones.