The effect of laser irradiation on contrast and image quality of infrared window materials

The aim of this study is to investigate the degradation of image quality due to the increased absorption of (IR) window materials such as germanium, silicon at elevated temperatures. In a prior study, it was observed that high-energy laser irradiation on the front window of a thermal camera caused the resulting image to become foggy and eventually disappear. Although the laser's wavelength is not transmitted by the IR window, its irradiance is partially absorbed, causing the germanium lens to heat up and become opaque, emitting its own thermal IR light which is detected by the sensor. This fogging effect can persist for several seconds after the laser is turned off. This provides a way to temporarily dazzle optical sensors with high-energy lasers without causing permanent damage, this is called pseudo-inband dazzling The primary objective of this study is to evaluate the degree of image quality degradation caused by the loss of contrast resulting from pseudo-inband dazzling. The transmission and emissivity of the windows are evaluated at different temperatures by observing them through portholes using a thermal camera. Additionally, a target with known temperature contrast is observed to directly assess the loss of contrast. The study evaluates not only germanium but also silicon windows using a medium and long wave infrared camera.