Characterization of Thin Polymers for Infrared Windows

There is an increasing number of applications for rapid deployment mid-wave infrared (MWIR) and long-wave infrared (LWIR) optical systems, especially for proof-of-concept. These systems are typically placed in test environments where they need an environmental enclosure window for protection. Traditional IR windows, like Germanium and Zinc Selenide, often have high costs and long fabrication lead times, especially for custom designs. Thin, readily available polymers have potential of solving this problem where they may have high enough transmission in the IR to be of use as an inexpensive environmental enclosure window. This paper outlines 33 polymer materials that have been tested as candidates for IR windows by measuring transmission and reflection and then calculating values of refractive index and extinction ratio from the measurements. We have identified 7 polymer materials as having high enough transmission to be used as an IR window. Further testing was done to characterize wavefront error and image quality of MWIR and LWIR cameras with these polymer windows. The combined results show 3 promising materials in the MWIR and LWIR.