When light waves hit a surface, they tend to bend in a particular direction, while at the same time slowing down by a factor of around 5. Called the refractive index, this trait has been heavily studied in optical physics. Now, experts can create materials that have a negative refractive index.
What this means is that light waves hitting these structures bend at the wrong angle. This is made possible by the use of metamaterials, synthetic materials developed in a manner that enables them to handle electromagnetic radiation like no naturally occurring material can.
In nature, all objects have a positive refractive index. Metamaterials are the only structures that have a negative refractive index. What researchers at the Harvard University School of Engineering and Applies Sciences
(SEAS) did was develop a technique for creating the most extreme metamaterial ever.
Working together with colleagues at the Weizmann Institute of Science, in Israel, the SEAS experts were recently able to demonstrate a new way of achieving negative refraction in metamaterials.
The index that can now be produced is as large as -700, which is more than 100 times larger than any other ever obtained. Details of exactly how this was made possible were published in the August 2 issue of the top scientific journal Nature.
“This work may bring the science and technology of negative refraction into an astoundingly miniaturized scale, confining the negatively refracting light into an area that is 10,000 times smaller than many previous negative-index metamaterials,” principal study investigator Donhee Ham explains.
The researcher holds an appointment as the Harvard Gordon McKay professor of electrical engineering and applied physics at SEAS. He says that the latest experiments the team conducted used microwaves. However, the approach is meant to be used with light spanning the entire electromagnetic spectrum.
Their test device can only operate at temperatures below 20 Kelvin, because it uses microwaves. The team hypothesizes that using terahertz radiation would enable the instrument to function at room temperature.
One of the most interesting applications for the new achievement is the miniaturization of existing metamaterials. This class of structures is currently heavily researched, primarily because it has numerous potential uses in military technology.
Metamaterials are currently the leading candidates for developing a so-called invisibility cloak, a device capable of obscuring an object hidden behind it from view, at multiple wavelengths. Scientists say the technology is still a few years away.
SEAS experts say that the US Air Force Office of Scientific Research provided the funds needed for this investigation.