Optics breakthrough may lead to better night vision devices

Scientists have developed 'perfect' thin film light absorbers, a breakthrough that may lead to low-cost infra-red technology for improved night vision devices.
The findings may help save millions of dollars in defence and other areas using sensing devices, and boost applications of technology to a host of new areas, such as agriculture.
Infra-red devices are used for improved vision through fog and for night vision and for observations not possible with visible light; high-quality detectors cost about USD 100,000 and some require cooling to minus 200 degrees Celsius.
Researchers at the University of Sydney demonstrated a dramatic increase in the absorption efficiency of light in a layer of semiconductor that is only a few hundred atoms thick - to almost 99 per cent light absorption from the current inefficient 7.7 per cent.

The team discovered perfect thin film light absorbers could be created simply by etching grooves into them, said Martijn de Sterke from the University of Sydney.
"Conventional absorbers add bulk and cost to the infrared detector as well as the need for continuous power to keep the temperature down. The ultrathin absorbers can reduce these drawbacks," de Sterke said.

"By etching thin grooves in the film, the light is directed sideways and almost all of it is absorbed, despite the small amount of material - the absorbing layer is less than 1/2000th the thickness of a human hair," he said.

Bjorn Sturmberg, who carried out the research as a PhD student at the University of Sydney, said the findings did not rely upon a particular material but could be applied to many naturally occurring weak absorbers.
"There are many applications that could greatly benefit from perfectly absorbing ultra-thin films, ranging from defence and autonomous farming robots to medical tools and consumer electronics," Sturmberg said.
The structures were much simpler to design and fabricate than using existing thin film light absorbers, which required either complex nanostructures, meta-materials and exotic materials or difficult-to-create combinations of metals and non-metals, said Lindsay Botten, Director of Australia's National Computational Infrastructure (NCI).

"There are major efficiency and sensitivity gains to be obtained from making photo-detectors with less material," Botten said.
The findings appear in the journal Optica.