The new generation of FIR thermal imagers require extremely high optical image quality to fully exploit the very high sensitivity available from detector arrays of several thousands of very small elements. Earlier optical designs and builds for FIR cameras generally suffer from a change in image quality arising from the change in refractive index of germanium. This paper shows that there are optical configurations whose image quality is virtually independent of temperature. A demonstrator using these optical designs is presently under construction jointly funded by the UK DRA and Pilkington Optronics. The demonstrator will be used to assess the practical performance of a camera designed to meet the very high specifications demanded of the next generation of thermal cameras.
Don R. Barron,
"Aberration athermal optics for second-generation FIR thermal imagers", Proc. SPIE 2744, Infrared Technology and Applications XXII, (27 June 1996); doi: 10.1117/12.243491; https://doi.org/10.1117/12.243491