Development of an Apparatus for the Determination of Spectral Reflectivity at High Temperatures in the Visible

The paper presents a reflectometer for high temperature measurements. In this apparatus, the directional-hemispherical spectral reflectivity is measured by comparing the optical response of the sample to white light with the response of a reference material. The reflected light, collected by an iIntegrating sphere, is dispersed in a spectrograph and detected by an ICCD camera. This procedure allows the simultaneous measurement of the reflectivity in a large, continuous wavelength range (presently 510 to 860 nm). An electrical resistance heater is used to heat the samples up to about 1200 K; for higher temperatures a flashlamp pumped dye laser is used. To avoid laser induced plasma generation, the iIntegrating sphere is placed inside a vacuum chamber, which also allows measurements under a controlled atmosphere. The response of the apparatus is calibrated to an absolute scale which allows the determination of the sample temperature by fitting the thermal emission spectrum with Planck’s formula. To check the performance of the apparatus, measurements on Fe2O3 (hematite) and NiO have been carried out.