Light-scattering Nanoparticles Could Lead to Invisbility Cloaks and Smaller Optical Antennas

Dexter Johnson 
http://spectrum.ieee.org/nanoclast/semiconductors/materials/light-scattering-nanoparticles-could-lead-to-smaller-optical-antennas

Photo: A*STAR Data Storage Institute

A research team from A*STAR Data Storage Institute in Singapore and St. Petersburg University in Russia has discovered certain light-scattering properties of nanoparticles that could lead to smaller and more effective optical nanoantennas and even invisibility cloaks.

The research, which was published in the journal ACS Photonics, took the form of numerical calculations of the light-scattering properties of dielectric nanoparticles, which are nanoparticles that are electrical insulators and can be polarized by an applied electric field.

One of the key attributes of the transparent nanoparticles modeled by the researchers is that they had a refractive index above two. All materials in nature have a refractive index—a measurement of the speed of light through that material. A refractive index above two it means that light can travel two times faster through a vacuum than through it.

The other key attribute of the nanoparticle models was their shape. The researchers calculated that if a sphere-shaped nanoparticle had a refractive index above 3.5 and its major axis is just over twice the length of its minor axis, it was possible to maximize its forward scattering of light.

This implies that if you manipulate the size and aspect ratio of the nanoparticle, you can determine how it will scatter light. This would be useful in applications such as photovoltaics as well as in metamaterials, where an artificially structured material is fabricated by assembling different objects to replace the atoms and molecules that one would see in a conventional material. This artificial structure results in a material with very different electromagnetic properties than those found in naturally occurring or chemically synthesized materials, which has lead to several research efforts into things like invisibility cloaks.

"Dielectric particles with optimized shapes which behave as very efficient directional antennas can be used in sensing devices, transmission lines, metasurfaces with numerous uses and in many other devices such as negative refractive index lenses, optical cloaking devices or nanolasers," said Boris Luk'yanchuk of A*Star, the lead researcher in the study, in a press release.

Luk'yanchuk and his colleagues will continue looking at applying their observation of these transparent to creating nanoscale devices and metamaterials.