Temporal cloaking time experiment

[waltky]

Neat trick could be useful for stealth technology...

Time cloaking: how scientists opened a hidden gap in time
January 4, 2012 - Scientists say they have achieved 'temporal cloaking' – manipulating light in a way that makes it appear as if 50 trillionths of a second never happened. Now, they'll try to expand the gap.

Forget wrapping an object – say, Harry Potter – in a cloak of invisibility. How about hiding an event using time? What may be a distant dream for this year's Indianapolis Colts has been demonstrated for the first time by a team of physicists at Cornell University. The approach is dubbed "temporal cloaking," and it builds on experiments researchers have already conducted to demonstrate that they can hide objects from view. Indeed, scientists had already succeeded at "spatial cloaking," which involves bending light around an object in such a way as to make it appear invisible. Temporal cloaking involves interrupting light to create a seeming gap in time in which an event can be hidden.

At this point, the time gap that the scientists created is so brief – about 50 trillionths of a second – that practical implications are barely a gleam in anyone's eye. But the researchers are interested in trying to lengthen the amount of time a beam's gap remains open, says Alexander Gaeta, who led the team reporting the results in the Jan. 5 issue of the journal Nature. In essence, the team briefly turned off a laser beam in a way that instruments receiving the beam could not detect. An observer would have no clue that the beam had blinked, and so would have no evidence of anything that happened to the beam in that 50 trillionths of a second. University of Rochester physicists Robert Boyd and Zhimin Shi, who are not members of Dr. Gaeta's team, liken the phenomenon to traffic at a railroad crossing.

The crossing gate falls, interrupting traffic (the laser beam) as the commuter train passes. From the perspective of the train, for a brief period there is no traffic and it can freely pass (the hidden event). Yet once the gate rises, traffic resumes and speeds up. To an observer a mile or two away, the flow of traffic shows no evidence of interruption – no evidence from traffic flow that a train had ever been there. How did the team open a gap in the laser beam? The researchers took advantage of the fact that when light travels through a material, different colors travel at different speeds. To alter colors in a segment of the laser beam, the researchers used a laser-based device dubbed a time lens.

Typical glass lenses bend light, changing its distribution in three-dimensional space. Time lenses, on the other hand, "do really funny things" to light, altering its traits for a defined period of time, Gaeta says. In this case, the team's modified time lenses briefly gave two adjoining segments of the green beam a red and a blue hue. When the segments passed through a specially designed length of optical fiber, the red light slowed and the blue light accelerated. The difference opened a gap in the beam – no light – that lasted about 50 trillionths of a second. Coming out the other side, the researchers reversed the process, slowing the blue and speeding the red, then passing them through another time lens to returning the beam to its original green color, leaving no hint of its temporary alteration. Well, almost no hint.

To see if their technique could hide an event from view, scientists shot a different laser beam into the gap. Usually, when two laser beams interact, the effects are easy to spot. In this case, though, the effects were more than 10 times weaker than they would have been if there had been no temporal cloaking. For now, much work will focus on gaining a clearer understanding of the physics involved and how to take advantage of them, says Dr. Shi of Rochester. Still, he adds, the basic physics of spatial cloaking and temporal cloaking are mathematically similar. With the addition of a cloaking approach that "plays tricks with time" to the other approach of playing tricks with light's distribution around an object in space, "hopefully we can find an easier way to create effective cloaking."

Source

 

[waltky]

Granny says it'd be a good way fer Obama to sneak up on Ahmadinejad an' smack him upside the back o' the head...

Scientists in US a step closer to 3D ‘invisibility cloak’
Fri, Jan 27, 2012 - Scientists in the US reported a further step toward a celebrated “invisibility cloak” by masking a large, free-standing object in three dimensions.

The laboratory work is the latest advance in a scientific frontier that uses novel materials to manipulate light, a trick that is of huge interest to the military in particular. Reporting in the New Journal of Physics, researchers at the University of Texas in Austin cloaked an 18cm cylindrical tube from light in the microwave part of the energy spectrum. Those hoping for a Harry Potter-style touch of wizardry would be disappointed. To the human eye, which can only perceive light in higher frequencies, the tube would not have been invisible at all , but the researchers said the experiment is important proof of a principle that so-called plasmonic meta-materials can achieve a cloaking effect.

A warplane cloaked with such materials could achieve “super-stealth” status by becoming invisible in all directions to radar microwaves, co-lead researcher Andrea Alu said. Plasmonic meta-materials are composites of metal and non-conductive synthetics made of nanometer-sized structures that are far smaller than the wavelength of the light that strikes them. As a result, when incoming photons hit the material, they excite currents that make the light waves scatter. The new experiment entailed making a shell of plasmonic meta-materials and placing the cylinder inside, then exposing the combination to microwaves.

Microwaves scattered by the shell ran into microwaves bounced from the object, preventing them sending a return signal to the viewer. “When the scattered fields from the cloak and the object interfere, they cancel each other out, and the overall effect is transparency and invisibility at all angles of observations,” Alu said. Any shape of object can be masked, he added. The feat is a step forward because other techniques have entailed bending light around two-dimensional objects or, in 3D, masking microscopic bumps on mirrors or reflectors, an approach called “carpet cloaking,” the authors said. The new concept could be modified for visible light, although any cloaked objects would be very small, in the micrometer range, as the plasmonic effect is linked to the wavelength of the light, Alu said in a telephone interview.

Even so, there could be important applications for microwave meta-materials, he said. “Camouflaging to radar is one important application, a super-stealth device to make objects invisible to radar,” he said. “What we are thinking about is not necessarily cloaking the whole warplane, but some hotspots, a part such as the tailplane that you would want to cloak because it reflects most of the energy [from microwave radar].” Another outlet would be in laboratories, filtering out the “backscatter” of light from the tip of high-powered optical microscopes. Unwanted light such as this impairs images of the object that is being scrutinized and skews measurements.

Scientists in US a step closer to 3D ?invisibility cloak? - Taipei Times

 

[waltky]

Uncle Ferd could use dat when Granny throws the skillet at him...

'Deflector shield' technology tested
Nov. 13,`12 (UPI) -- A device capable of diverting electromagnetic radiation to produce a "deflector shield" has been tested by U.S. company Fractal Antenna Systems.

Fractal Antenna said the device is a variation of the invisibility cloak technology invented by its Chief Executive Officer Nathan Cohen. "A deflector shield uses cloak technology not to hide an object but to pass radiation around it," Cohen said. "There is no attempt to 'image.' Not only is the power deflected safely to the other side but there is virtually no change to the object caused by the radiation pressure, unlike a mirror or an absorber.

"There is no 'bounce back'. This is truly a new and novel technology." The deflector shield used in the test was constructed as a vest and worn by one of the firm's team. The vest comprised an inner copper layer and fractal-shaped meta-materials conforming around it.

In the test, 90 percent of the electromagnetic power from microwaves aimed at the subject passed around him. Cohen is to demonstrate the technology Friday at the Radio Club of America in New York, the company said.

Read more: 'Deflector shield' technology tested by Fractal Antenna Systems - UPI.com