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Nanometer device improves optical sensing

Posted: 20 Aug 2013 ?? ?Print Version ?Bookmark and Share

Keywords:superlens? nanoantenna? numerical modelling?

A team of researchers at the A*STAR Institute of High Performance Computing Singapore has proposed a novel approach to 'superlens' systems that they believe can surpass the classical limit of focusing light. According to them, conventional lenses, made of shaped glass, are limited in how precisely they can redirect beams of incoming light and make them meet at a point. They used numerical modelling to develop the design. Concentrating radiation into a smaller volume in this way enhances the interaction between light and matter, and thus the concept could prove useful in highly sensitive sensors of the future, the researchers stated.

Light is a type of wave. Unlike the rise and fall in sea water at a beach, however, a light wave consists of oscillating electric and magnetic fields. The wavelengththe distance a wave travels in one oscillation cycleimposes a limit on the minimum size to which light can be focused. However, this limit does not apply over small distances that are comparable to the wavelength, which is known as the near-field regime.

The researchers designed a silver nanostructure embedded in glass. Their device combined two separate elements. One component was a nanoantennasimilar to the RF antennas used to detect TV-carrying signals, but reduced in size to match the wavelength of optical radiation. The other component was a superlens made of a thin slab of silver. The purpose of the superlens was to move the light detected by the nanoantenna into an imaging plane.

The team mathematically modelled the optical response of this device to an incoming beam of red light. They then altered the dimensions of the structure to maximise the enhancement in electric field. In this way, they were able to show that a 20nm-thick superlens, separated by 34nm from an antenna made of two silver ellipses, could increase the electric field of light by a factor of 250.

Confining light into these super intense 'hot-spots' could prove a boon for optical detection systems.

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