Scattering lens yields unprecedentedly sharp images

Scientists from the MESA+ Institute of the University of Twente, the University of Florence and the FOM Institute AMOLF have developed a strongly scattering lens, which makes it possible to see tiny structures of less than 100 nm with visible light.

This is an unprecedentedly sharp image that beats even the most expensive microscope objectives. The results will be published next week in the leading American journal Physical Review Letters (expected publication date 29 April, online 28 April) and the article has been highlighted as an Editors’ suggestion.

One focus
When laser light is scattered - for example by a piece of paper - a disorderly pattern of small bright spots, known as speckles, is created. The same happens in the new lens. It is made from a material with a high refractive index, which makes the speckles very small and sharp. However, to make a sharp image you need a small focus instead of a dense speckle pattern. The researchers therefore adjusted the phase of the laser light to prepare this for the scattering. That allows the speckles to slides over each other, so that the light is focused on a single point. This focus can be moved freely in the object plane of the lens. The researchers tested their lenses on several gold spheres and were able to depict these images with a sub-100 nm resolution.

High resolution
This is the first lens capable of resolving nanostructures with visible light. The secret is the small and movable focus. The scattering lens can be combined with numerous modern microscopic techniques so that the resolution can be improved even further.

Further information
Elbert G. van Putten +31 (0)53 489 5391
Allard P. Mosk +31 (0)53 489 5394

Reference
'Scattering lens resolves sub-100 nm structures with visible light'
E.G. van Putten, D. Akbulut, J. Bertolotti, W.L. Vos, A. Lagendijk, A.P. Mosk
Link to preprint: arxiv.org/abs/1103.3643

Figure 1. Comparison of light focusing with a conventional lens and a scattering lens. (a) A plane light wave sent through a normal convex lens forms a focus. The focal size is determined by the range of angles in the converging beam and by the refractive index of the medium in which the light propagates itself. The microscope image shows a collection of gold spheres, as imaged with a high-quality commercial microscope objective. Inset on the left is a photo of a normal lens. (b) The researchers illuminate a scattering material with a high refractive index with a shaped wave. The light is carefully phased so that - after all the scattering - it forms a perfectly spherical, converging wave front in the object plane of the scattering lens. The large range of angles contributing to the converging beam, combined with the high refractive index, gives rise to a nanometer-sized focal point. The microscope image on the right shows the same collection of gold spheres as in (a) but imaged with the much higher resolution of the scattering lens. Inset on the left is a photo of the lens. The upper layer has been made porous and is therefore scattering.