December 08, 2016

Thin film nanocrystal from Australia could make thin as glass night vision goggles that do not need external power

Scientists at The Australian National University (ANU) have designed a nano crystal around 500 times smaller than a human hair that turns darkness into visible light and can be used to create light-weight night-vision glasses.

Professor Dragomir Neshev from ANU said the new night-vision glasses could replace the cumbersome and bulky night-vision binoculars currently in use.

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

"This tiny device could have other exciting uses including in anti-counterfeit devices in bank notes, imaging cells for medical applications and holograms."

Co-researcher Dr Mohsen Rahmani said the ANU team's achievement was a big milestone in the field of nanophotonics, which involves the study of behaviour of light and interaction of objects with light at the nano-scale.

"These semi-conductor nano-crystals can transfer the highest intensity of light and engineer complex light beams that could be used with a laser to project a holographic image in modern displays," said Dr Rahmani, a recipient of the Australian Research Council (ARC) Discovery Early Career Researcher Award based at the ANU Research School of Physics and Engineering.

The material can make infrared light visible, raising the possibility of night-vision goggles as thin as glass and free of external power. Conventional night vision goggles look a bit like binoculars and require electricity. Here’s how they work: An “objective lens” in front collects low-level and near-infrared light, whose photons are converted by a photocathode into electrons. The goggles use thousands of volts of electricity to send the electrons down a vacuum-sealed tube into a plate with millions of tiny holes. Pushing the electrons through the holes releases other electrons in a chain reaction called cascaded secondary emission. The effect: where there was one electron, there are now hundreds, all in the same pattern as the original photons. When the electrons hit the final layer, which is covered in phosphorescent material, what was dark becomes light.

Nanoletters - Nonlinear Generation of Vector Beams From AlGaAs Nanoantennas

The quest for nanoscale light sources with designer radiation patterns and polarization has motivated the development of nanoantennas that interact strongly with the incoming light and are able to transform its frequency, radiation, and polarization patterns. Here, we demonstrate dielectric AlGaAs nanoantennas for efficient second harmonic generation, enabling the control of both directionality and polarization of nonlinear emission. This is enabled by specialized III–V semiconductor nanofabrication of high-quality AlGaAs nanostructures embedded in optically transparent low-index material, thus allowing for simultaneous forward and backward nonlinear emission. We show that the nanodisk AlGaAs antennas can emit second harmonic in preferential direction with a backward-to-forward ratio of up to five and can also generate complex vector polarization beams, including beams with radial polarization.

PhD student Maria del 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," said Ms Camacho-Morales from the Nonlinear Physics Centre at ANU.

SOURCES- Defense One, Australian National University, Nanoletters

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