Nanoantenna splits light
11 Nov 2011 by hjqbcptqcm.d hjqbcptqcm.d
Swedish scientists have developed a nanoantenna that can act as a router for red and blue light, even though the antenna is smaller than the wavelength of light. The finding from the team at the Chalmers University of Technology could lead to optical nanosensors being able to detect very low concentrations of gases or biomolecules.
The researchers employed a completely new method to control visible light using asymmetric material composition. This means that although the antenna – which consists of one silver and one gold nanoparticle about 20 nanometres apart on a glass surface – shouldn’t be able to scatter light, it does.
Experiments show pairs of closely spaced disks show phase accumulation through material-dependant Plasmon resonances – the antenna scatters visible light so that red light goes in one direction, and the blue light in the other.
“The explanation for this exotic phenomenon is optical phase shifts,” said Timur Shegai. “The reason for this is that nanoparticles of gold and silver have different optical properties, in particular different Plasmon resonances.”
Plasmon resonance means that the free electrons of the nanoparticles oscillate strongly in pace with the frequency of light, said Shegai, which in turn affects light propagation even though the antenna is so small.
Researchers now have a whole new parameter for controlling the light and believe nanoplasmonics can be applied to a variety of new areas.
One example is optical sensors, where you can used plasmons to build sensors which are so sensitive that they can detect much lower concentrations of toxins or signalling substances than is possible today,” said Mikael Käll. “This may involve detection of single molecules in a sample, for example, to diagnose diseases at an early stage, which facilitates quick initiation of treatments.”
Researchers have shown that the antennas are easy to build and can be fabricated densely over large areas using cheap colloidal lithography. They have published their work in Nature Communication.
