Environmental testing of long-wavelength infrared (LWIR) windows

Accurate and reliable testing is paramount to the development of LWIR window materials. Without appropriate characterization and testing, improvements to existing technologies are impossible to document with certainty. Reliable and repeatable testing provides the data needed to measure advancements and identify improvements in any technology. No single test can be completely definitive, and the continuous evaluation of emerging technologies using different test methods under varying conditions is critical when evaluating a new materials' capability. The environmental testing of infrared (IR) window materials has traditionally consisted of rain erosion testing, single impact water jet testing, and sand erosion testing. While these three tests provide the materials engineer with significant insight into the durability of a window material, these tests have generally ignored the combined effect of rain and sand. This paper looks at the combined effect of rain and sand erosion on a standard LWIR window material, zinc sulfide (ZnS).