* Astronomy

Title: All-angle negative refraction and active flat lensing of ultraviolet light
Authors: Ting Xu, Amit Agrawal, Maxim Abashin, Kenneth J. Chau & Henri J. Lezec

Decades ago, Veselago predicted that a material with simultaneously negative electric and magnetic polarisation responses would yield a 'left-handed' medium in which light propagates with opposite phase and energy velocities - a condition described by a negative refractive index. He proposed that a flat slab of left-handed material possessing an isotropic refractive index of -1 could act like an imaging lens in free space. Left-handed materials do not occur naturally, and it has only recently become possible to achieve a left-handed response using metamaterials, that is, electromagnetic structures engineered on subwavelength scales to elicit tailored polarisation responses. So far, left-handed responses have typically been implemented using resonant metamaterials composed of periodic arrays of unit cells containing inductive-capacitive resonators and conductive wires. Negative refractive indices that are isotropic in two or three dimensions at microwave frequencies have been achieved in resonant metamaterials with centimetre-scale features. Scaling the left-handed response to higher frequencies, such as infrared or visible, has been done by shrinking critical dimensions to submicrometre scales by means of top-down nanofabrication. This miniaturisation has, however, so far been achieved at the cost of reduced unit-cell symmetry, yielding a refractive index that is negative along only one axis. Moreover, lithographic scaling limits have so far precluded the fabrication of resonant metamaterials with left-handed responses at frequencies beyond the visible. Here we report the experimental implementation of a bulk metamaterial with a left-handed response to ultraviolet light. The structure, based on stacked plasmonic waveguides, yields an omnidirectional left-handed response for transverse magnetic polarisation characterised by a negative refractive index. By engineering the structure to have a refractive index close to -1 over a broad angular range, we achieve Veselago flat lensing, in free space, of arbitrarily shaped, two-dimensional objects beyond the near field. We further demonstrate active, all-optical modulation of the image transferred by the flat lens.

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Berkeley Lab Researchers Make First Perovskite-based Superlens for the Infrared
 
Superlenses earned their superlative by being able to capture the "evanescent" light waves 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, but their use has been limited because most have been made from elaborate artificial constructs known as metamaterials. The unique optical properties of metamaterials, which include the ability to bend light backwards - a property known as negative refraction - arise from their structure rather than their chemical composition. However, metamaterials can be difficult to fabricate and tend to absorb a relatively high percentage of photons that would otherwise be available for imaging.
Now, researchers with the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab) have fabricated superlenses from perovskite oxides that are  simpler and easier to fabricate than metamaterials, and are ideal for capturing light in the mid-infrared range, which opens the door to highly sensitive biomedical detection and imaging. It is also possible that the superlensing effect can be selectively turned on/off, which would open the door to highly dense data writing and storage.

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