Researchers have developed a breakthrough technique that enables them to build ‘invisible’ materials out of light.
The method uses light like a needle to thread long chains of particles.
And, the scientists claim, it could be an important step towards building invisibility cloaks.
The research, published in the journal Nature Communications, describes how engineering materials at a nanoscale level can induce invisibility.
Materials just a few billionths of a metre across can be built to alter the way in which light passes through them.
Known as a ‘metamaterial’, these can be designed to reflect light in the ‘wrong’ way.
A metamaterial is an artificial material that has been engineered to have properties different to those found naturally in nature.
This technique involves stitching gold nanoparticles together in long strings, which is achieved by using unfocused laser light as a ‘needle’.
These strings are then stacked in layers on top of one another, allowing materials to be made in high quantities.
When light is shone upon an object it is either reflected or absorbed, dictating how it appears to a human eye.
This means that by using such metamaterials, the interaction of particles with light can be changed so that the object appears invisible, or as something completely different.
While the effect has been known of for some time, scaling it up to a useful size had proved problematic.
But the University of Cambridge researchers have proposed this novel solution that they say makes it possible.
The strings of particles are connected using barrel-shaped molecules known as cucurbiturils (CBs), which can be used to control the spacing between nanoparticles and lock them in place.
Cucurbiturils are like molecular handcuffs – molecules which can be used to hold other molecules together.
In this research, Cucurbiturils were used like tile spacers, so that all of the gold nanoparticles could be held at a uniform distance before connecting them to make the finished material.
Using ultrafast lasers, these so-called ‘bridges’ can then be made to form and hold the nanoparticles together in long strings.
‘It’s about finding a way to control that bridge between the nanoparticles,’ said Dr Ventsislav Valev of the University’s Cavendish Laboratory, one of the authors of the paper.
‘Joining a few nanoparticles together is fine, but scaling that up is challenging.
‘We have controlled the dimensions in a way that hasn’t been possible before.
‘This level of control opens up a wide range of potential practical applications.’
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