Night-vision security cameras could be getting a lot less costly, thanks to the discovery that their lenses can be made from silicon. Ordinarily, thermal infrared camera lenses are made from materials such as germanium and chalcogenide, which are much more expensive.

Silicon normally doesn't work for such lenses, as the material tends to absorb too much light, allowing little to get through to the camera's image sensor. A team of French researchers, however, discovered that this isn't a problem if the lens is very thin. They proceeded to laser-etch a Fresnel-style silicon lens, in which light is focused using concentric rings of material.

The finished lens is approximately 1 mm thick, 4 mm in diameter, has a 130-degree field of view, and works over a wide range of infrared wavelengths. While the images it captures may not be exactly broadcast-quality, they're sufficient for picking up individuals in low-light settings.

The team is made up of staff from aerospace lab ONERA, thermal imaging sensor company ULIS, the Institut d’Optique and the French National Center for Scientific Research. A paper on their research was recently published in the journal Optics Letters.

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