Optical degradation of germanium with elevated temperature: Consequences for infrared imaging systems

This study examines the effect of elevated temperatures, simulated using a climate chamber, on the optical
transmission of germanium (Ge) windows used in thermal infrared devices. Both anti-reflection (AR) coated and
uncoated germanium windows were analyzed over a temperature range of 20 ◦ C to 180 ◦ C using a radiometrically
calibrated long-wave infrared imager. Significant optical degradation was observed beginning around 60 ◦ C, a
temperature relevant to standard operational thresholds for military systems. The experimental results closely
align with theoretical predictions for the temperature sensitivity of germanium absorption coefficients, thereby
validating the approach. These findings offer important insights into how high-energy laser irradiation causes
temperature-driven optical degradation, emphasizing the susceptibility of Ge optics in thermal imaging systems
under extreme conditions. A reproducible, non-destructive method is proposed for evaluating these effects