Analysis and correction of stray thermal radiation in infrared optical systems including an experimental case study.

Abstract

In infrared systems, the stray radiation from optical elements and mechanical structures is an important factor affecting quantitative measurements because the irradiance on detectors due to stray radiation depends on the operating temperature of the optical system. Without correcting for this effect, the accuracy of quantitative measurements made with such systems is degraded. To better understand this phenomenon, we derive herein a mathematical model that describes stray radiation as a function of temperature and use the model to quantitatively analyze the stray radiation of an infrared system at different operating temperatures. To test the theory, we use it to calculate the stray radiation from an experimental infrared system comprising a Cassegrain reflector in the first stage and a transmission mirror in the second stage. The maximum relative error between theory and experiment was 8.72%. At the same time, a corrective measure of stray radiation is provided to account for the effect of stray radiation on quantitative measurements. The relative error of quantitative measurements decreases from 2.16% to 0.31%. The measurement accuracy of the infrared system has been improved effectively.