Thermal imaging using sulfur polymer optics.

Infrared thermal imaging is used in defence, security cameras, fire detection, planetary science, driver assist capabilities, medical thermography, and other safety applications. Unfortunately, the lenses for infrared cameras are made from expensive or restricted materials such as germanium, silicon, or chalcogenide glass. Furthermore, these inorganic lenses are made by low throughput milling processes, and they are difficult to repair or recycle. There is a need for low cost and sustainable lens materials that can be mass-produced to prescription. Sulfur-derived polymers, made from widely available elemental sulfur, are promising candidates due to their high refractive index and mid-wave infrared (MWIR) and long-wave infrared (LWIR) transparency. However, most of these polymers reported to date are still limited in their LWIR transmittance and the glass transition temperature required for shape persistence. Recently, a polymer containing a sulfurized norbornane microstructure was predicted by Pyun, based on theoretical considerations, to address these issues. However, this polymer has not yet been made due to complex side reactions encountered in previously attempted syntheses. Here, we overcome these challenges and prepare this polymer for the first time, demonstrate methods for high throughput molding and recycling, and validate its use as a lens in a long-wave thermal imaging camera.