Press Release: Scattering lens yields unprecedented sharp images

Jacopo Bertolotti is a wikipedian friend. Some weeks ago he sent me his last paper, Scattering lens resolves sub-100 nm structures with visible light about a research work that he relised in Netherlands at Complex Photonic Systems (Institute for Nanotechnology, University of Twente). It's an interesting paper about the construction of the first lens that provides a resolution in the nanometer regime at visiblewavelengths (I read in the abstract).
In this moment I read the paper, that it is published on Phys. Rev. Lett. 106 on the 13rd May 2011, the black day of Blogger.
So, before a post in which I examine in details the paper, I decide to publish the official press release of the team:
It is generally believed that disorder always degrade the sharpness of optical images. Now scientists of the MESA+ Institute at the University of Twente, University of Florence and the FOM Institute AMOLF have shown that a scattering and disordered layer in conjunction with a high refractive index material can be used as an imaging device with a sub-100 nm resolution thereby beating the most expensive microscope objectives. The robustness of this scattering lens against distortion and aberrations, together with the ease of manufacturing and its very high resolution are highly favorable features to improve the performance of a wide range of cutting-edge microscopy techniques. The results are being published this Friday in the leading journal Physical Review Letters and are highlighted as an Editors' suggestion.

Even the most expensive microscope objectives offer only a limited resolution. This restriction is due to the wave nature of light that force any focus to be larger than half the wavelength of light (the diffraction limit). This theoretical limit is usually impossible to reach due to practical problems like aberrations that cause focal distortion. Paradoxically a completely disordered layer naturally creates very small and intense light spots when illuminated by a laser. The price to pay is that these spots, which are known as speckle, are arranged in a dense and random pattern making them useless for imaging purposes.
The new scattering lens developed by the scientists, uses light scattering to couple light efficiently into a high refractive index material. By a fine control over the light that illuminates the disordered layer they can concentrate the speckle spots in the same place, effectively creating a single very small focus. Taking advantage of what is known as the "memory effect" the scientists were able to scan this nano-sized focus in the object plane of the lens. They then placed small gold nano particles in the object plane and used the scattering lens to resolve the particles with a sub-100 nm resolution.
The combination of a high-index scattering material with the complete control over the illumination provides the first lens that is able to resolve nano-structures with visible light. The ability of this scattering lens to create small and scannable focuses makes it a favorable tool to improve the performance of all the imaging methods that require accurate focusing.

Comparison of light focusing with a conventional lens and a scattering lens. (a) A plane light wave sent through a normal lens forms a focus. The focal size is determined by the range of angles in the converging beam as and by the refractive index of the medium that the light is propagating in. The microscope image shows a collection of gold spheres as imaged with a commercial high quality oil immersion microscope objective. Inset on left is a photo of an ordinary lens. (b) The scientists send a shaped wave through a scattering layer on top of a high refractive index material. The wave front is carefully shaped so that, after traveling through the layer, it forms a perfectly spherical, converging wave front. The large range of angles contributing to the converging beam, combined with the high refractive index, give rise to a nanometer-sized focal spot. The microscope image shows the same collection of gold spheres as in (a) imaged with the scattering lens. Inset on left is a photo of the lens with the scattering layer on top.

If you want read paper, but don't have the subscription to PRL, you can read arXiv preprint.

1 comment:

  1. Clever way of sacrificing brightness for resolution, as I understand it.


Markup Key:
- <b>bold</b> = bold
- <i>italic</i> = italic
- <a href="">FoS</a> = FoS