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Groovy light-absorbing films could boost night vision


Infrared technology may become a lot cheaper and easier to use. Belinda Smith reports.


Thin grooves, etched in a film, direct light sideways. The end result? Almost all light is absorbed. A smooth layer, though, will reflect light.
THOMAS P. WHITE, AUSTRALIAN NATIONAL UNIVERSITY

Physicists in Australia have made an ultra-thin film that absorbs almost 99% of light, simply by etching grooves into its surface.

The light-absorbing layer, which is only a few hundred atoms thick, could be used in applications "ranging from defence and autonomous farming robots to medical tools and consumer electronics", says co-lead author Björn Sturmberg from the University of Sydney.

In dark or dim conditions, or through fog or smoke, infrared cameras really shine.

As optical cameras detect visible light, infrared cameras create images from radiation with longer, infrared wavelengths invisible to our eyes but we feel as heat.

But the best absorbers must be kept cold – as low as -200 ºC – so they can pick up minute levels of infrared radiation, otherwise they risk "blinding" themselves with their own heat.

This cooling, of course, uses energy. So to make more efficient detectors, thinner infrared-absorbing layers are key.

Previous studies have tried building nanostructures or use complex combinations of metals and non-metals with varying degrees of success, with one thing in common – they're not particularly easy to produce.

Sturmberg, co-lead author Teck Chong from Australian National University in Canberra and colleagues found etching 41-nanometre grooves into a layer of antimony sulfide drastically improved the material's ability to absorb light with a wavelength of 591 nanometres from around 8% to 98.7%.

It does this by bouncing almost all photons of that particular wavelength sideways, where they're absorbed rather than reflected off the surface.

While 591-nanometre-wavelength light falls in the visible spectrum – it's a shade of amber – the width and spacing of the grooves can be modified to suit other wavelengths, they write.

The work was published in the journal Optica.

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Belinda Smith is a science and technology journalist in Melbourne, Australia.