We're one step closer to creating invisibility cloaks, thanks to
researchers from Cambridge University who have just published a study detailing how to build materials with light.
The research team have developed a technique that involves controlling the way light flies through minuscule building blocks that are billionths of a metre across in order to obscure them from the human eye. When these blocks are all joined together, the effect works cumulatively, so whole chunks of the material can disappear at once.
The entire effect is dependent on the way light interacts with the material, and the material needs to be capable of controlling that relationship, rather than simply absorbing or reflecting light, as the majority of materials do. And this is exactly what the researchers have achieved. By engineering at nanoscale, they have been able to produce metamaterials that refract light in unusual directions, rather than simply reflecting it, which can potentially render the materials invisible.
Joining the blocks of material together is no easy feat though.
The process involves using unfocused laser light as billions of needles to stitch gold nanoparticles together into strings. The strings can then be stacked on top of one another, something the researchers compare to building with Lego bricks.
So how close are we to getting our hands on that invisibility cloak? Firstly, the technique used to build bridges between the nanoparticles needs to be improved so that it is easier to scale up. The particles need to be attached electronically as traditional welding techniques would melt them. There is a knack to doing this and it involves spacing the material blocks carefully and accurately using barrel-shaped molecules called cucurbiturils so that it's as easy as possible to retain control over the process.
These molecules ensure that the strings are "primed for re-sculpting", according to the paper, which was
published today in the journal Nature Communications.
When ultrafast lasers are pointed at the molecules, ripples of electrons are produced at the surface of the metals. The laser beam interacts with these skipping electrons, which concentrate the light energy on atoms at the surface and joins them to form bridges between the nanoparticles. As the lasers are able to build billions of these bridges in rapid sucession, the nanoparticles can quickly be threaded into long strips. "We have controlled the dimensions in a way that hasn't been possible before," said Cambridge University's Ventsislav
Valev, who worked with researchers on the project. "This level of control opens up a wide range of potential practical applications."
Among these potential use cases are several, particularly in the development of military stealth technology, that have been on the minds of many for some time, but have always been considered impossible as they haven't before been scaleable -- a problem this new project is expected to solve.
This article was originally published by WIRED UK
