Scientists have developed a ’Harry Potter-style’ ultra-thin invisibility cloak that can conform to the shape of tiny objects and conceal them from detection with visible light.
Although this cloak is only microscopic in size, the principles behind the technology should enable it to be scaled-up to conceal macroscopic items as well, researchers said.
Working with brick-like blocks of gold nanoantennas, the researchers fashioned a “skin cloak” barely 80 nanometres in thickness, that was wrapped around a three-dimensional object about the size of a few biological cells and arbitrarily shaped with multiple bumps and dents.
The surface of the skin cloak was meta-engineered to reroute reflected light waves so that the object was rendered invisible to optical detection when the cloak is activated.
“This is the first time a 3D object of arbitrary shape has been cloaked from visible light,” said corresponding author Xiang Zhang, director of US Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) Materials Sciences Division. “Our ultra-thin cloak now looks like a coat. It is easy to design and implement, and is potentially scalable for hiding macroscopic objects,” Zhang said.
It is the scattering of light - be it visible, infrared or X-ray - from its interaction with matter that enables us to detect and observe objects.
Curving light
The rules that govern these interactions in natural materials can be circumvented in metamaterials whose optical properties arise from their physical structure rather than their chemical composition.
For the past ten years, Zhang and his research group have been pushing the boundaries of how light interacts with metamaterials, managing to curve the path of light or bend it backwards, phenomena not seen in natural materials, and to render objects optically undetectable.
In the past, their metamaterial-based optical carpet cloaks were bulky and hard to scale-up, and entailed a phase difference between the cloaked region and the surrounding background that made the cloak itself detectable - though what it concealed was not.
In the study, when red light struck an arbitrarily shaped 3D sample object measuring approximately 1,300 square microns in area that was conformally wrapped in the gold nanoantenna skin cloak, the light reflected off the surface of the skin cloak was identical to light reflected off a flat mirror, making the object underneath it invisible even by phase-sensitive detection.
The cloak can be turned “on” or “off” simply by switching the polarisation of the nanoantennas.
The study was published in the journal Science.