Night-vision glasses: Nanocrystals developed at ANU allow direct vision into the infrared

Night-vision glasses: Nanocrystals developed at ANU allow direct vision into the infraredImagine seeing colours in the infrared, or gaining night vision simply by putting on a pair of glasses.

Humans can see in a tiny bandwidth of the light spectrum: infrared, ultraviolet, and x-rays are invisible to us.

Night-vision goggles have helped us peer into the infrared and see light emitted from bodies, animals, objects in the form of heat or thermal radiation.

But those goggles are clunky. They take photons, light particles, convert them to electricity, then beam them into your eyes as photons again.

Researchers at the Australian National University have now fabricated tiny crystals that "blueshift" infrared light directly into to the visible spectrum.

By applying them to a thin film on glass, they hope to eventually make glasses that give us a direct view into the infrared.

"The nano crystals are so small they could be fitted as an ultra-thin film to glasses to enable night vision," said Professor Dragomir Neshev from the Nonlinear Physics Centre within the ANU.

The tiny crystals - 500 times narrower than a human hair - are made of aluminium-gallium-arsenide, a stable semiconducting alloy used in mobile phones.

The crystals act as antennaes that receive a photon emitted in the infrared, combine them with a photon from a laser and then "upconvert" the combined photon to the visible spectrum.

"It's conceivable that this technology will allow us to see colours in the infrared," said lead researcher of the study, Professor Dragomir Neshev.

"Warmer should look bluish and cooler would seem reddish," he said. "But we won't really know until we see it ourselves."

At present, the technology has converted single frequency, high-intensity laser infrared light into the visible spectrum.

So how will they work with multifrequency, diffuse light emitted by warm objects at night?

"Different sized crystals can convert different frequencies of the infrared to visible," Professor Neshev said.

The light at night is very different to focused laser light. The researchers are looking to build a prototype device using a small integrated laser such as that found in a DVD player or a laser pointer. It will require a small battery to power the laser.

"The thin film on the glass will act as a laser guide," Professor Neshev said. Interacting with the infrared photons from a thermal body, the laser photons will help boost the light to the visible spectrum.

His colleague, Mohsen Rahmani, said: "You can fit four or five million crystals on a one square millimetre substrate." There would be hundreds of millions of these on the surface of a pair of glasses.

PhD student Rocio Camacho-Morales said the team built the device on glass so that light can pass through, which was critical for optical displays.

"This is the first time anyone has been able to achieve this feat, because growing a nano semi-conductor on a transparent material is very difficult," she said.

They hope within five years they will have a prototype of their invention that will allow the production of affordable, lightweight night-vision glasses, as simple to wear as a pair of sunnies.

Professor Neshev said they are discussing their next steps with DARPA, a research and development arm of the US Department of Defence.

As well as the obvious military applications, Professor Neshev and Dr Rahmani said there are plenty of civilian possibilities.

"[It could be used] in anti-counterfeit devices in bank notes, imaging cells for medical applications and holograms," Professor Neshev said.

Dr Rahmani said: "We should be able to apply to any glass surface, such as your car windscreen, which could help with night driving safety."

The research was published in Nanoletters and presented this week to the Australian Physics Congress in Brisbane.
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