A novel high temperature optical probe

When a dielectric stack of 1/4 wave layers is deposited on an optical surface, a narrow band of wavelengths will be reflected. The peak reflection shifts with temperature change of the dielectric stack. This spectral shift is caused by the dn/dT and dL/dT of the film stack. Using a solid state spectrometer, the spectral shift can be traced to measure the temperature change. Currently, we can accurately measure temperatures from liquid nitrogen temperature to 1200°C using a silica fiber. By depositing high temperature dielectric layers on a sapphire disc, we can measure temperature from the back reflected light of this disc, which can be mounted at the end of a small alumina tube. A collimation lens is used for illumination and collection of the reflected light signal from the disk. We have developed a sensitive algorithm for accurately tracing the spectral shift and converting this spectral shift into temperature.