Effect of the radiative property change of interference optical filter on the accuracy of a linear pyrometer

Abstract

Abstract The multilayer interference filter is an optical component of several optical devices. One such instrument is an infrared thermometer. In a radiation thermometer, optical filters are used to select a specific wavelength range of the radiation signal for detection. The interference filters change their multilayer structure due to variation in the surrounding temperature. There are instances where these variations are big enough to cause an error in temperature measurement. Determining and analysing the extent of this effect is crucial in a high accuracy calibration process. In this paper, we attempted to quantify the effect of temperature variation in the optical thickness of each layer of the interference filter and, subsequently, on its performance. The interference filter design model is modified to accommodate the temperature dependence by considering the therm-optic effect of each dielectric material, medium and substrate. The results showed how the temperature change effect (that was translated into temperature measurement error) could be minimised by optimising the layer thickness of carefully chosen materials with a minimised cumulative therm-optic coefficient effect.