Light - Astronomy News

Blobrana

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Posts: 131433

Date: Sep 22 23:30 2011

RE: Light	Permalink

Speed of light 'broken' by scientists Einstein's theory of special relativity, proposed in 1905, states that nothing in the universe can travel faster than the speed of light in a vacuum. But researchers at the CERN lab near Geneva claim they have recorded neutrinos, a type of tiny particle, travelling faster than the barrier of 299,792 kilometres per second. The results have so astounded researchers that American and Japanese scientists have been asked to verify the results before they are confirmed as a discovery. Read more __________________

Blobrana

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Posts: 131433

Date: Apr 22 21:37 2010

Negative-index metamaterial	Permalink

A group of scientists led by researchers from the California Institute of Technology (Caltech) has engineered a type of artificial optical material - a metamaterial - with a particular three-dimensional structure such that light exhibits a negative index of refraction upon entering the material. In other words, this material bends light in the "wrong" direction from what normally would be expected, irrespective of the angle of the approaching light. This new type of negative-index metamaterial (NIM), described in an advance online publication in the journal Nature Materials, is simpler than previous NIMs - requiring only a single functional layer - and yet more versatile, in that it can handle light with any polarization over a broad range of incident angles. And it can do all of this in the blue part of the visible spectrum, making it "the first negative index metamaterial to operate at visible frequencies," says graduate student Stanley Burgos, a researcher at the Light-Material Interactions in Energy Conversion Energy Frontier Research Centre at Caltech and the paper's first author. Read more __________________

Blobrana

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Posts: 131433

Date: Sep 18 21:01 2008

CPT Violation	Permalink

Title: Astrophysical Tests of Lorentz and CPT Violation with Photons Authors: Alan Kostelecky, Matthew Mewes A general framework for tests of Lorentz invariance with electromagnetic waves is presented, allowing for operators of arbitrary mass dimension. Signatures of Lorentz violations include vacuum birefringence, vacuum dispersion, and anisotropies. Sensitive searches for violations using sources such as active galaxies, gamma-ray bursts, and the cosmic microwave background are discussed. Direction-dependent dispersion constraints are obtained on operators of dimension 6 and 8 using gamma-ray bursts and the blazar Markarian 501. Stringent constraints on operators of dimension 3 are found using 5-year data from the Wilkinson Microwave Anisotropy Probe. No evidence appears for isotropic Lorentz violation, while some support at one sigma is found for anisotropic violation. Read more (206kb, PDF) __________________

Blobrana

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Posts: 131433

Date: Aug 11 01:27 2008

Metamaterials	Permalink

Scientists have created two new types of materials that can bend light the wrong way, creating the first step toward an invisibility cloaking device. One approach uses a type of fishnet of metal layers to reverse the direction of light, while another uses tiny silver wires, both at the nanoscale level. Both are so-called metamaterials -- artificially engineered structures that have properties not seen in nature, such as negative refractive index. Read more __________________

Blobrana

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Posts: 131433

Date: Jul 9 10:15 2008

Ultrahigh-Energy Photons	Permalink

Title: Lorentz Violation and Ultrahigh-Energy Photons Authors: Matteo Galaverni (Bologna University), Guenter Sigl (Hamburg University) The propagation of photons, electrons and positrons at ultra-high energies above 10^{19} eV can be changed considerably if the dispersion relations of these particles are modified by terms suppressed by powers of the Planck scale. We recently pointed out that the current non-observation of photons in the ultra-high energy cosmic ray flux at such energies can put strong constraints on such modified dispersion relations. In the present work we generalize these constraints to all three Lorentz invariance breaking parameters that can occur in the dispersion relations for photons, electrons and positrons at first and second order suppression with the Planck scale. We also show how the excluded regions in these three-dimensional parameter ranges would be extended if ultra-high energy photons were detected in the future. Read more (466kb, PDF) __________________

Blobrana

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Posts: 131433

Date: Dec 31 12:32 2007

RE: Light	Permalink

Title: Bounds on the fine structure constant variability from FeII absorption lines in QSO spectra Authors: Paolo Molaro, Dieter Reimers, Irina I. Agafonova, Sergei A. Levshakov The Single Ion Differential alpha Measurement (SIDAM) method for measuring fine structure variations (daa)and its figures of merit are illustrated together with the results produced by means of FeII absorption lines of QSO intervening systems. The method provides daa ~= -0.12(± 1.79) ppm (parts-per-million) at zabs = 1.15 towards HE 0515--4414 and daa = 5.66(±2.67) ppm at zabs= 1.84 towards Q 1101--264, which are so far the most accurate measurements for single systems. SIDAM analysis for 3 systems from the Chand et al. (2004) sample provides inconsistent results which we interpret as due to calibration errors of the Chand et al. data at the level of about 10 ppm. In one system evidence for photo-ionisation Doppler shift between MgII and FeII lines is found. This evidence has important bearings on the Many Multiplet method where the signal for daa variability is carried mainly by systems involving MgII absorbers. Some correlations are also found in the Murphy et al. sample which suggest larger errors than previously reported. Thus, we consider unlikely that both the Chand et al. and Murphy et al. datasets could provide an estimate of daa with an accuracy at the level of 1 ppm. A new spectrograph like the ESPRESSO project will be crucial to make progress in the astronomical determination of daa. Read more (196kb, PDF) __________________

Blobrana

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Posts: 131433

Date: Nov 24 16:02 2007

Fundamental constant alpha	Permalink

A row over the apparent wandering ways of one of the universe's fundamental constants has been fuelled by claims that a crucial study on one side of the debate suffered from "basic flaws". The story began in 1998 when John Webb of the University of New South Wales (UNSW) in Sydney, Australia, claimed that alpha, a constant which determines how matter and photons interact, was smaller 12 billion years ago than it is today. His finding was based on measurements of the frequencies at which interstellar gas clouds appeared to absorb light emitted from very bright objects known as quasars when the universe was young. Variation in this constant over time would have deep implications, and some physicists say it points to the existence of the extra dimensions required by string theory. What's more, alpha governs the strength of electromagnetic interactions, the vacuum energy of empty space, and the strength... Read more (Subscription) __________________

Blobrana

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Posts: 131433

Date: Nov 21 21:43 2007

photonic crystals	Permalink

Faster and more efficient thanks to "defects" Three-dimensional photonic crystals will revolutionise telecommunications/BASF scientists research in the EU project "NewTon" Smaller, faster, more efficient: BASF research scientists are helping to revolutionise the future world of telecommunications with the aid of three-dimensional... Read more Smaller, faster, more efficient: BASF research scientists are helping to revolutionise the future world of telecommunications with the aid of three-dimensional photonic crystals. In a three-year project, BASF is researching into the development of these crystals together with partners such as Hanover Laser Centre, Thales Aerospace Division, Photon Design Ltd., the Technical University of Denmark and the Ecole Nationale Supérieure des Télécommunications de Bretagne. By the end of 2008, the partners in the "NewTon" project expect to have developed the first functional components of this new technology. The long-term goal is to use three-dimensional photonic crystals as construction elements in telecommunication. Half of the project is being funded by the European Union. Read more __________________

Blobrana

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Posts: 131433

Date: Nov 14 19:35 2007

Metamaterials	Permalink

Since their invention in 2000, exotic materials called metamaterials have revealed many uses such as perfect lenses or invisibility cloaks. But now computer simulations performed by physicists in the UK suggest another application slowing down a rainbow of light to a standstill. Their idea could be the first route to storing broadband, optical communications at room temperature. Read more __________________

Blobrana

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Posts: 131433

Date: Jun 20 20:14 2007

Nanolaser	Permalink

Scientists at Yokohama National University in Japan have built a highly efficient room-temperature nanometer-scale laser that produces stable, continuous streams of near-infrared laser light. The overall device has a width of several microns (millionths of a meter), while the part of the device that actually produces laser light has dimensions at the nanometer scale in all directions. The laser uses only a microwatt of power, one of the smallest operating powers ever achieved. This nanolaser design should be useful in future miniaturized circuits containing optical devices. The researchers present their nanolaser in the latest issue of Optics Express, an open-access journal published by the Optical Society of America, one of the ten Member Societies of the American Institute of Physics. The laser is made of a semiconductor material known as gallium indium arsenide phosphate (GaInAsP). The laser's small size and efficiency were made possible by employing a design, first demonstrated at the California Institute of Technology in 1999, known as a photonic-crystal laser. In this design, researchers drill a repeating pattern of holes through the laser material. This pattern is called a photonic crystal. The researchers deliberately introduced an irregularity, or defect, into the crystal pattern, for example by slightly shifting the positions of two holes. Together, the photonic crystal pattern and the defect prevent light waves of most colours (frequencies) from existing in the structure, with the exception of a small band of frequencies that can exist in the region near the defect. Read more __________________

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