- Number 336 |
- May 2, 2011
Berkeley Lab invents a new kind of superlens for the infrared
Perovskite superlens setup
Superlenses have resolution far greater than diffraction-limited conventional optics, but most are made from hard-to-fabricate metamaterials. Now researchers with DOE’s Lawrence Berkeley National Laboratory have made superlenses from much simpler layered oxides known as perovskites. Ideal for capturing light in the mid-infrared range, the new perovskite superlenses open the door to highly sensitive biomedical detection and imaging.
Ordinary optics are limited by diffraction, the bending or spreading of light that prevents the resolution of objects smaller than about half a wavelength – the so-called far field. Another kind of light exists in the near field, a standing wave of “evanescent” light that peaks about a third of a wavelength from an illuminated surface or boundary and then precipately decays with distance. Superlenses capture this evanescent light and add its reconstructed image to that created by conventionally focused propagating waves.
Until now, most superlenses have done the trick using special materials with negative refraction, in which evanescent waves are reinforced rather than attentuated by backward bending of the illuminating light – a property arising from the material’s structure. These metamaterials are not only difficult to make, they tend to absorb many of the photons that would otherwise be available for imaging.
The new perovskite superlens developed by Ramesh Ramamoorthy’s group in Berkeley Lab’s Materials Sciences Division is not only easy to make and has low absorption losses, it has very high resolution.
“Spectral studies of the lateral and vertical distributions of evanescent waves around the image plane of our lens show that we have achieved an imaging resolution of one micrometer, about one-fourteenth of the working wavelength,” says Ramesh.
“Our perovskite-based superlens doesn’t focus propagating waves, but instead reconstructs evanescent fields only,” says Susanne Kehr, formerly with Ramesh’s group and now at the University of Saint Andrews in the United Kingdom. “These fields generate the sub-wavelength images that we study with near-field infrared microscopy.”
It may also be possible to selectively turn the superlensing effect on and off, which would open the door to high-density data writing and storage."Perovskites display a wide range of fascinating properties," says Yongmin Liu, with Kehr one of the authors of the Nature Communications paper reporting the results. “Their ferroelectricity, piezoelectricity, superconductivity, and enormous magnetoresistance might inspire new functionalities ... such as non-volatile memory, microsensors and microactuators, and applications in nanoelectronics.”
[Paul Preuss, 510.486.6249,