Mid-IR Lens Incorporates Waste Sulfur

Thin, inexpensive plastic lenses for IR imaging devices can be manufactured from waste sulfur generated by refining fossil fuels.

The plastic is transparent to wavelengths from 3 to 5 µm, has a refractive index between 1.865 and 1.745, and has high optical focusing power, according to researchers from the University of Arizona. Most polymers have refractive indices below 1.6 and transmit much less midrange IR, the researchers said.

Inexpensive sulfur lenses can be manufactured using waste sulfur and an additive in liquid form, baked in a conventional oven using a silicone mold. Images courtesy of the University of Arizona.

The team successfully took thermal images of a person through a piece of the new plastic. By contrast, taking a picture through the plastic often used for ordinary lenses does not show a person's body heat.

"We have for the first time a polymer material that can be used for quality thermal imaging, and that's a big deal," said Jeffrey Pyun, associate professor of chemistry at UA. "The industry has wanted this for decades."

The lenses could be used for anything involving heat detection and infrared light, such as handheld cameras for home energy audits, night-vision goggles, perimeter surveillance systems and carbon dioxide detection, said Robert A. Norwood, a UA professor of optical sciences.

The left-hand image of University of Arizona researcher Jared Griebel was taken with an IR camera with an ordinary plastic lens, which does not transmit IR light. The image of Griebel on the right was taken through a piece of the new sulfur-based plastic.

The researchers have filed an international patent for their new chemical process and its application for lenses.

Research funding was provided by the American Chemical Society Petroleum Research Foundation, the US National Science Foundation, the National Research Foundation of Korea, the Korean Ministry of Education, Science and Technology, the State of Arizona Technology Research Initiative Fund and the US Air Force Office of Scientific Research. The work is published in Advanced Materials (doi: 10.1002/adma.201305607).

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