09 May 2011
metamaterial breaks new ground
with the highest refractive index of any known substance.
Illustration of the metamaterial
consisting of ‘I’-shaped metal wires
When a light beam crosses from one medium to another, it’s path is altered by refraction according the refractive indices of the two mediums and the wavelength of light.
The refractive indices of common materials like glass and water are in the range of 1.3 to 1.5, and the values for natural materials seldom exceed 8-10.
Researchers from the Korea Advanced Institute of Science and Technology have now developed an artificial ‘metamaterial’ with a peak refractive index of more than 38 - higher than for any substance known.1
Metamaterials are artificial constructs consisting of microstructures designed to interact with light in some very unusual ways.
By their nature and specificity of design, however, these microstructures are generally able to interact only with light in specific and narrow wavelength bands, and the development of metamaterials with high refractive index over a broad wavelength range remains a challenge.
The metamaterial developed by Min and
his team consists of thin ‘I’-shaped metal wires separated by narrow
gaps (see image above), resulting in a broadband refractive index of more
than 20. More remarkably, the refractive index peaks at 38.6 at the
resonance frequency of close to 0.5 THz.
This new development expands the realm of what is achievable with regard to the refractive properties of metamaterials, which have previously been shown to be capable of negative refractive indices - an unnatural property that could lead to the development of perfect lenses and even invisibility or cloaking devices.
The latter are complex designs based on the concept of ‘transformation optics’ and typically combine a range of refractive indices in a single device design.