Influence of temperature-dependent refractive index on thermal radiation from surface gratings

We set up a high-temperature ellipsometry system for the measurement of optical constants n and k. The n and k values of refractory metals of W and Mo were measured from the visible (VIS) to near infrared (NIR) wavelength range at several temperatures by means of the system. The n drastically increases especially in the NIR region, while the k is almost invariant in all the range with increasing temperatures. Numerical simulation based on rigorous coupled-wave analysis (RCWA) with the values of n and k measured by high-temperature ellipsometry is qualitatively coincident with the measured spectral emissivity at high temperature. It has revealed that spectral emissivity has temperature dependence especially in the NIR region.