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World record for shortest controllable time

Lasers can now generate light pulses down to 100 attoseconds thereby enabling real-time measurements on ultrashort time scales that are inaccessible by any other methods. Scientist at the Max Born Institute for Nonlinear Optics and Short Time Spectroscopy (MBI) in Berlin, Germany have now demonstrated timing control with a residual uncertainty of 12 attoseconds. This constitutes a new world record for the shortest controllable time scale.
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NIST detector counts photons with 99 percent efficiency

Scientists at the National Institute of Standards and Technology (NIST) have developed the world's most efficient single photon detector, which is able to count individual particles of light travelling through fibre optic cables with roughly 99 percent efficiency. The team's efforts could bring improvements to secure electronic communication, advanced quantum computation and the measurement of optical power.
Using essentially the same technology that permitted them to achieve 88 percent detection efficiency five years ago, the team has enhanced its ability to detect photons largely by improving the alignment of the detector and the optical fibres that guide photons into it. The basic principle of the detector is to use a superconductor as an ultra-sensitive thermometer. Each individual photon hitting the detector raises the temperature - and increases electrical resistance - by a minute amount, which the instrument registers as the presence of a photon.
According to team member Sae Woo Nam, the advantage of this type of single photon detector is that the new detector design not only measures lower levels of light than have ever been possible, but does so with great accuracy.

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Title: Resolution of the Abraham-Minkowski Dilemma
Authors: Stephen M. Barnett 

The dilemma of identifying the correct form for the momentum of light in a medium has run for a century and has been informed by many distinguished contributions, both theoretical and experimental. We show that both the Abraham and Minkowski forms of the momentum density are correct, with the former being the kinetic momentum and the latter the canonical momentum. This identification allows us to explain why the experiments supporting each of the rival momenta gave the results that they did. The inclusion of dispersion and absorption provides an interesting subtlety, but does not change our conclusion.

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A recent paper by Hinds (Imperial College) and Barnett has proposed a resolution of the century-old problem of the form of optical momentum inside a medium
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Ed
~ Photon momentum (in a medium) equals nhk according to Minkowski, or hk/n according to Abraham...

-- Edited by Blobrana on Saturday 27th of February 2010 02:28:33 AM

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Physicists play Lego with photons

While many of us enjoyed constructing little houses out of toy bricks when we were kids, this task is much more difficult if bricks are elementary particles. It is even harder if these are particles of light - photons, which can only exist while flying at an incredible speed and vanish if they touch anything.
A team at the University of Calgary has accomplished exactly that: by manipulating a mysterious quantum property of light known as entanglement, they are able to mount up to two photons on top of one another to construct a variety of quantum states of light - that is, build two-story quantum toy houses of any style and architecture.
The results of their research, written in the paper 'Quantum-optical state engineering up to the two-photon level', will be published on Nature Photonics's website on Feb. 14.

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The remarkable feat of tying light in knots has been achieved by a team of physicists working at the universities of Bristol, Glasgow and Southampton, reports a paper in Nature Physics this week.
Understanding how to control light in this way has important implications for laser technology used in wide a range of industries.

"In a light beam, the flow of light through space is similar to water flowing in a river.  Although it often flows in a straight line - out of a torch, laser pointer, etc - light can also flow in whirls and eddies, forming lines in space called 'optical vortices'.  Along these lines, or optical vortices, the intensity of the light is zero (black). The light all around us is filled with these dark lines, even though we can't see them" - Dr Mark Dennis, University of Bristol, lead author of the paper.

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Electromagnetically induced transparency (EIT) is a coherent optical nonlinearity which renders a medium transparent over a narrow spectral range within an absorption line. Extreme dispersion is also created within this transparency "window" which leads to "slow light"
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Title: How Holes Can Obscure the View: Suppressed Transmission through an Ultrathin Metal Film by a Subwavelength Hole Array
Authors: Julia Braun, Bruno Gompf, Georg Kobiela, and Martin Dressel

If a metal film, thick enough to be totally opaque, is perforated by tiny subwavelength holes in an orderly fashion, the transmission will be enhanced extraordinarily. Here, we investigate the transmission through an ultrathin semitransparent Au film with a square array of subwavelength holes and observe the opposite behaviour: less light is transmitted through the pierced metal compared to the closed film.

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Scientists at the University of Adelaide have made a breakthrough that could change the world's thinking on what light is capable of.
The researchers in the University's new Institute for Photonics & Advanced Sensing (IPAS) have discovered that light within optical fibres can be squeezed into much tighter spaces than was previously believed possible.
Optical fibres usually act like pipes for light, with the light bouncing around inside the pipe. As you shrink down the size of the fibre, the light becomes more and more confined too, until you reach the ultimate limit - the point beyond which light cannot be squeezed any smaller.
This ultimate point occurs when the strand of glass is just a few hundred nanometres in diameter, about one thousandth of the size of a human hair. If you go smaller than this, light begins to spread out again.
The Adelaide researchers have discovered they can now push beyond that limit by at least a factor of two.

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A brilliant young physicist Joćo Magueijo  asks the heretical question: What if the speed of light - now accepted as one of the unchanging foundations of modern physics - were not constant?
Magueijo, a 40-year old native of Portugal, puts forth the heretical idea that in the very early days of the universe light travelled faster - an idea that if proven could dethrone Einstein and forever change our understanding of the universe. He is a pioneer of the varying speed of light (VSL) theory of cosmology -an alternative to the more mainstream theory of cosmic inflation- which proposes that the speed of light in the early universe was of 60 orders of magnitude faster than its present value.

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Ed ~ we can place a limit on the variability of the speed of light by looking at the glow from the first stars, soon after the big bang; we know that the speed cannot have changed significantly. Also there is no reason, or purpose, to supposing that the speed of light was vastly faster than today.  The inflation theory already solves many of the problems of early cosmology.

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