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Simplified superlens captures IR light

Photonics Spectra
Jun 2011
Compiled by Photonics Spectra staff

BERKELEY, Calif. – Superlenses that are ideal for capturing light in the mid-infrared range now can be fabricated more easily. Made from perovskite oxides rather than metamaterials, these new devices could open the door to highly sensitive biomedical detection and imaging.

It’s possible that the superlensing effect can be selectively turned on and off, which would enable highly dense data writing and storage, researchers at Lawrence Berkeley National Laboratory report.

With the ability to capture the evanescent lightwaves that blossom close to an illuminated surface and never travel far enough to be “seen” by a conventional lens, superlenses hold enormous potential in a range of applications, depending upon the form of light they capture. However, their use has been limited because most have been made from metamaterials, which can be difficult to fabricate and tend to absorb a relatively high percentage of photons that otherwise would be available for imaging.

Superlenses overcome the diffraction limit by capturing the evanescent lightwaves, which carry detailed information about object features that are significantly smaller than incident light wavelengths; evanescent waves dissipate after a very short distance and seldom reach conventional lenses.

The scientists demonstrated a superlens for electric evanescent fields with low absorption losses using perovskites in the mid-infrared regime. Their spectral studies of lateral and vertical distributions of the evanescent waves around the image plane of the lens showed that they had achieved an imaging resolution of 1 μm, about 1/14 of the working wavelength, they said.

The perovskites they used to make their superlens, bismuth ferrite and strontium titanate, feature a low rate of photon absorption and can be grown as epitaxial multilayers whose highly crystalline quality reduces interface roughness so there are few photons lost to scattering. The combination of low absorption and scattering losses significantly improves the imaging resolution of the superlens. Additionally, its ferroelectricity, piezoelectricity, superconductivity and magnetoresistance could inspire new functionalities of perovskite-based superlenses, including nonvolatile memory, microsensors, microactuators and nanoelectronics, the scientists said.

The research, published in the March 22, 2010, issue of Nature Communications (doi: 10.1038/ncomms1249), represents the first application of perovskite materials to superlensing.


GLOSSARY
ferroelectricity
The phenomenon whereby certain crystals exhibit spontaneous electric polarization. It is analogous with ferromagnetism.
image plane
A plane in which an image is formed. A real image formed by a positive lens would be visible upon a screen located in this plane.
lens
A transparent optical component consisting of one or more pieces of optical glass with surfaces so curved (usually spherical) that they serve to converge or diverge the transmitted rays from an object, thus forming a real or virtual image of that object.
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