# Thermal imaging using sulfur polymer optics

## TL;DR

Researchers developed a low-cost sulfur-based polymer for infrared thermal imaging lenses, offering a sustainable and efficient alternative to expensive materials like germanium.

## Contribution

The first successful synthesis of a sulfur-based polymer with high mid-wave and long-wave infrared transparency, suitable for thermal imaging lenses.

## Key findings

- A sulfur-based polymer with high MWIR and LWIR transparency was successfully synthesized.
- The polymer allows for high-throughput molding and recycling, addressing sustainability issues.
- The material was validated as a functional lens in a long-wave thermal imaging camera.

## Abstract

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.

Thermal imaging lenses are typically made from expensive materials such as germanium and silicon. Here, the authors synthesise a sulfur-based polymer with high mid-wave infrared and long-wave infrared transparencies, presenting a high-performing, low-cost alternative to traditional thermal imaging lens materials.