Engineers produce lens that overcomes diffraction limits

US engineers have succeeded in creating a near-perfect ‘superlens’ that uses the principles of metamaterials to overcome conventional diffraction limits.

The lenses could be used in ultra-high-resolution microscopes and more precise lasers for the microfabrication of electronic components.  

Optical lenses are limited by the nature of light — the so-called diffraction limit — and do not generally allow visualisation of objects smaller than 200 nanometres across, about the size of the smallest bacterium.

Other researchers have also been able to sidestep the diffraction limit, but not throughout the entire spectrum of visible light.

In the latest work, however, a team from Michigan Technological University showed how metamaterials could be ‘stretched’ to refract light waves from the infrared all the way past visible light and into the ultraviolet spectrum.

The key lies in plasmons — charge oscillations near the surface of thin metal films that combine with special nanostructures. When excited by an electromagnetic field, they gather light waves from an object and refract it in a way not seen in nature, a phenomenon called negative refraction. This enables the lens to overcome the diffraction limit.

The team believes it could also be applied to lithography, the microfabrication process used in electronics manufacturing.

‘The lens determines the feature size you can make, and by replacing an old lens with this superlens, you could make smaller features at a lower cost,’ said project lead Prof Durdu Guney of Michigan Tech. ‘With this superlens, you could use a red laser — like the pointers everyone uses — and have simple, cheap machines, just by changing the lens.’

The superlenses might also allow the visualisation of objects as small as viruses in reasonably compact microscope units.