14 DAY TRIAL // Invisibility cloaks moved out of the realm of science fiction, and into reality, several years ago, but scientists are still having problems covering some regions of the electromagnetic spectrum. Now, a team of experts says that optical cloaks could be based on nanoscale silicon spheres.
The same materials have been recently used to create invisibility cloaks that work in the microwave portion of the electromagnetic spectrum, and physicists are keen on learning whether the nanospheres can be used for optical wavelengths as well.
These building blocks are very easy to use and produce. Experts from the Australian National University, in Canberra, hope to be able to use them for optical cloaks. If this is possible, then these devices could be created at relatively low costs, and employed for several practical applications.
A working invisibility cloak is unlikely to hit store shelves any time soon. Researchers have indeed made considerable progress when it comes to understanding the theoretical foundations of what they need to accomplish, but they are still far from covering all bases.
Theoretical progress has however led to the creation of increasingly complex and potent cloaking devices, especially for radio and microwave wavelengths. Now, scientists want to further up the electromagnetic spectrum, to infrared, optical and ultraviolet light.
Microwave cloaks work because they are made up of split ring resonators, devices shaped like the letter “C” that have electric and magnetic fields which interact with incoming electromagnetic waves in such a way that the object they conceal is cloaked from view.
The reason these resonators are easy to make is that microwaves have centimeter-scale wavelengths. Since the C-shaped devices need to be smaller than the wavelength of the type of light they are trying to redirect, they are relatively easy to produce.
However, the wavelength of optical light has only a few hundred nanometers, which means that the resonators need to be smaller than that. At this scale, most metals tend to absorb visible light, rather than transmit it, which results in significant losses.
The Australian team says that replacing the resonators with silicon nanospheres some 100 to 200 nanometers in diameter could provide the necessary cloaking capabilities for optical wavelengths, Technology Review reports.
“These optical systems open up new perspectives for fabrication of low-loss optical metamaterials and nanophotonic devices,” the researchers write in a paper published in the online journal arXiv.