A team of experts from the Massachusetts Institute of Technology (MIT), in Cambridge, announces the development of a new type of metamaterials, which they say can absorb light at multiple wavelengths with extreme efficiency.
The accomplishment could open the way for a brand-new generation of optical sensors and advanced solar cells, which would take advantage of all available photons in their environment. This could lead to high conversion rates, enough maybe to allow renewable energy to compete with fossil fuels.
Metamaterials represent a class of artificial substances that are manmade, and do not occur in nature. They are designed in such a way that they can complete tasks which no other material can, such as for instance bending light.
This class of materials is currently being used to create advanced superlenses, innovative antennae systems, extreme-sensitivity detectors and invisibility cloaks that hide objects from light at multiple wavelengths. All this is made possible by the metamaterials' own internal structure.
What the MIT team did was basically extend the range of uses for which these materials are well suited. Rather than bending photons around an object – such as in an invisibility cloak – the substances created at the Institute can absorb light particles with extreme efficiency.
In fact, members of the group say, the materials can trap light traveling at multiple wavelengths, which means that optical detectors based on them could be sensitive to infrared and ultraviolet light as well.
MIT Department of Mechanical Engineering professor Nicholas X. Fang says that the new metamaterials use a pattern of wedge-shaped ridges, which enable it to capture light at extremely varied angles of incidence.
Fang is also the Brit and Alex d’Arbeloff Career Development Associate Professor in Engineering Design at the Institute. The metamaterials he and his team developed are both lightweight and thin, making them very cost-effective to produce.
The expert compares the new material to the way the cochlea in the inner ear works. “Our ears separate different frequencies and gather them at different depths,” he says, adding that the wedges on the material ensure that different types of photons are harvested at different depths.
“What we have done is to design a multilayer sawtooth structure that can absorb a wide range of frequencies” with an efficiency of more than 95 percent, adds MIT postdoctoral student Kin Hung Fung. He is a co-author of a paper detailing the work, which appears in the latest issue of the esteemed journal Nano Letters.
Funding for this study was provided by the US National Science Foundation (NSF), the National Natural Science Foundation of China and the Asian Office of Aerospace Research and Development.