Manufacturing Bits: Aug. 28
University Claims Unilateral Invisibility
Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), one of the largest universities in Germany, has proved that unilateral invisibility is possible. In other words, an optical system can be “invisible” from one side and act like a mirror from the other side.
The development of photonic materials with these properties is aimed at optics and other applications. Current photonic-like metamaterials are based on the manipulation of light-refraction in the sub-wavelength range. This is referred to as “optical cloaks of invisibility,” according to researchers.
Light propagation also can be influenced by adjusting amplification and loss. This involves maintaining the parity-time symmetry (PT) so that light amplification and loss merge into each other in a space–time–reflection.
Experimental measurement (above) and artistic illustration (below) of unilateral invisibility: If the ray of light hits the medium from the left, the reflections at the red and blue scattering bodies made of PT-symme- trical material are even stronger than the ray of light itself. If the same ray of light hits the active elements from the right, the reflection is suppressed and the ray can travel through the elements without any obstacles —which means that the scattering bodies are invisible from the right. Source: FAU
In an experimental measurement, researchers proved this concept. If a ray of light hits the medium from the left, the reflections at the red and blue scattering bodies made of PT-symmetrical material are even stronger than the ray of light itself, according to the university.
If the same ray of light hits the active elements from the right, the reflection is suppressed and the ray can travel through the elements without any obstacles. This in turn means that the scattering bodies are invisible from the right, according to researchers.
FAU has succeeded in applying the principle to light pulses in large optical networks. Experiments have shown light travels in a different way than in conventional materials. The strength of the optical fields can change in certain parameter ranges, the flanks of light pulses travel beyond the speed of light, according to researchers.
Thanks to the correlation between amplification and loss, PT-symmetrical materials can become partially invisible. “When a ray of light hits one side of the medium, it is transmitted completely without any reflection at all—just as if there was no scattering body there,” said Ulf Peschel, a professor of FAU’s Institute for Optics, Information and Photonics.
The project brings together scientists from FAU’s Institute of Optics, Information and Photonics, the Cluster of Excellence Engineering of Advanced Materials (EAM), the Erlangen Graduate School in Advanced Optical Technologies (SAOT), the Max Planck Institute for the Science of Light and the University of Central Florida, Orlando.
New Form Of Carbon Is Discovered
A team of scientists have observed a new form of very hard carbon clusters that are capable of indenting diamonds. This finding has potential applications for a range of mechanical, electronic, and electrochemical uses.
Carnegie Institute of Washington’s Geophysical Laboratory led the research team. It collaborated with Argonne, Jilin University, the University of Nebraska, Stanford, and SLAC National Accelerator Laboratory.
Carbon is the fourth-most-abundant element in the universe. Some forms of carbon are crystalline. Other forms are amorphous. Hybrid products that combine both crystalline and amorphous elements have not previously been observed.
Researchers started with a substance called carbon-60 cages, made of organized balls of carbon constructed of pentagon and hexagon rings bonded together to form a round, hollow shape. An organic xylene solvent was put into the spaces between the balls and formed a new structure.
They applied pressure to this combination of carbon cages and solvent, to see how it changed under different stresses. At low pressure, the carbon-60’s cage structure remained. But as the pressure increased, the cage structures started to collapse into more amorphous carbon clusters.
However, the amorphous clusters still occupy their original sites, forming a lattice structure. The team discovered that there is a narrow window of pressure, about 320,000 times the normal atmosphere, under which this new structured carbon is created and does not bounce back to the cage structure when pressure is removed.
—Mark LaPedus
Tags: Carnegie Institute, Friedrich-Alexander-Universitat Erlangen, Jilin University, Max Planck Institute, optical cloaks, parity-time symmetry, SLAC, Stanford, University of Nebraska