Thursday, January 5, 2012

New "tricks" from science include spatial, temporal, aural, and plasmodic cloaking

And then shall that Wicked be revealed, whom the Lord shall consume with the spirit of his mouth, and shall destroy with the brightness of his coming:
Even him, whose coming is after the working of Satan with all power and signs and lying wonders,
II Thessalonians 2:8-9

And he doeth great wonders, so that he maketh fire come down from heaven on the earth in the sight of men,
And deceiveth them that dwell on the earth by the means of those miracles which he had power to do in the sight of the beast;
Revelation 13:13-14a

I don't know if these developments have any prophetic significance, but they're interesting. First, there was "spatial cloaking." As reported by Charles Q. Choi of The Christian Science Monitor, February 2, 2011:

An "invisibility cloak" that's able to hide items thousands of times larger than before now exists, scientists say.

The first hints that cloaking devices might one day become more than just a "Star Trek" fantasy began emerging five or so years ago, and since then researchers have made such cloaks a reality by warping light.

Light is often bent in nature. For instance, mirages form when desert sands heat air that bends light rays from up above, creating illusions of water that are really reflections of the sky. The cloaking devices that scientists have created smoothly guide rays of light completely around objects so they proceed along their original trajectory as if nothing were there.

However, the first cloaking devices researchers made were useless against the human eye. To start with, they were only effective on microwave rays, not visible light. They also only worked in two dimensions, and thus could not hide three-dimensional objects.

In 2010, scientists created the first cloak that worked for three-dimensional objects against light nearly visible to humans. Still, the cloaked area was only 30 microns wide, or about one-third the width of a human hair.

Now researchers have developed a cloak that can hide three-dimensional objects against red and green lasers and ordinary white light. Although the cloaked region they demonstrated is only three-quarters of an inch (2 centimeters) wide, "there is actually no limit on the size of the cloak," researcher Shuang Zhang, a physicist at the University of Birmingham in England, told LiveScience.

All invisibility cloaks demonstrated until now were made of artificial composite structures known as metamaterials. The fabrication techniques for these metamaterials are complex and time-consuming, yielding only tiny cloaks that could only hide similarly tiny objects limited to only a few wavelengths of light in size.

In contrast, this new cloak is made of prisms of naturally occurring calcite. These crystals are each about three-quarters of an inch wide on their longest sides, much larger than the parts seen in previous cloaks.

The scientists glued two of these prisms together, forming an arrowhead shape when seen from the side. The space, or bump, under the notch of this arrowhead and whatever is within is cloaked from view.

"The cloaks can be readily scaled up to hide larger objects," Zhang said. "It really depends on how large a calcite crystal we can find in nature. According to the literature, the largest calcite crystal has a scale of 7 meters by 7 meters by 2 meters (23 feet by 23 feet by 6.5 feet). Such a crystal would enable the construction of an invisibility cloak that can conceal object a few meters wide and at least 40 centimeters (16 inches) high."

This cloak does have a significant drawback — it depends on polarization of light. One can think of all light waves as either rippling up and down, left and right, or at any angle in between, a property known as polarization. This cloak only works for light of a specific polarization — "the bump will be seen by light of other polarizations," Zhang said.

Nevertheless, the cloak might still work in the real world, Zhang said. For instance, if the sun is low in the sky, sunlight streaming into the water "will be largely polarized, and an invisibility cloak sitting on the water floor will become invisible," he said. "There could be military applications — for example, to hide something such as submarine on the seafloor."

Also, while the bump at the bottom of the cloak is invisible, the cloak itself is still visible due to a slight reflection at the interface between the cloak and its surroundings. "This reflection can be significantly reduced by putting antireflection coating on the cloak or some other means," Zhang said.

"It is still challenging to make a 'Harry Potter' type of invisibility cloak that works in air and can hide very large objects," Zhang said. "Metamaterials could be a solution, but we will have a long way to go."

Zhang and his colleagues detailed their findings online Feb. 1 in the journal Nature Communications.

Now comes "temporal cloaking." As reported by Pete Spotts in The Christian Science Monitor, January 4, 2012:

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."

Then there's what might be called aural cloaking. As reported by David Skoumbourdis in The Epoch Times, January 5-11, 2012 (originally posted December 29, 2011, updated January 2, 2012):

Want to play music at night without bothering neighbors? Being annoyed by noises from the highway? Scientists at Germany’s Karlsruhe Institute of Technology (KIT) can help.

Inspired by the concept of an invisibility cloak that guides light waves around an object making it invisible, the researchers are developing a cloaking device that can render objects completely silent. This device uses a custom-engineered plastic material that guides sound waves around an object making it inaudible.

The material has a smart microstructure consisting of two polymers, one soft and one hard, which form a millimeter-thin plate. Sound waves are guided around a circular area in the plastic plate in such a way that vibrations can neither enter nor leave this area.

“Contrary to other known noise protection measures, the sound waves are neither absorbed nor reflected,” researcher Martin Wegener said in a press release. “It is as if nothing was there.”

The technology is presently only a proof of concept, but when mature, it could be effective at soundproofing and have a wide range of applications.

The study will be published in the journal Physical Review Letters.

February 6, 2012 update: Now comes "plasmonic cloaking." As reported by David Skoumbourdis in The Epoch Times, February 2-8, 2012 (originally posted January 29, 2012, updated February 5, 2012):

The invisibility cloak has taken yet another step toward realization, with U.S. researchers cloaking a three-dimensional object from microwaves for the first time using a technique dubbed “plasmonic cloaking.”

Previous research efforts have demonstrated cloaking two-dimensional (or flat) objects using metamaterials—artificial materials engineered to have special properties—that cause light to bend around them, creating a mirage-like effect.

Plasmonic cloaking differentiates itself with the use of plasmonic metamaterial that causes the scattered light from both the metamaterial and the cloaked object to collide and cancel out. This prevents the reflected light from the object reaching our eyes, making it invisible.

“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 observation,” said study co-author Andrea Alu in a press release.

“One of the advantages of the plasmonic cloaking technique is its robustness and moderately broad bandwidth of operation, superior to conventional cloaks based on transformation metamaterials. This made our experiment more robust to possible imperfections, which is particularly important when cloaking a 3-D object in free-space,” Alu said.

The researchers tested the material by coating a 7-inch cylinder with the plasmonic metamaterial. Microwaves were directed toward the cloaked cylinder and the resultant scattering was mapped. The results confirmed the anticipated performance of the material.

Prior experiments have demonstrated that the material can work with objects of varying shape. The one challenge remaining is to test plasmonic cloaking using visible light.

“In principle, this technique could be used to cloak light; in fact, some plasmonic materials are naturally available at optical frequencies. However, the size of the objects that can be efficiently cloaked with this method scales with the wavelength of operation, so when applied to optical frequencies we may be able to efficiently stop the scattering of micrometer-sized objects,” said Alu.

Despite the present theoretical limitations, Alu believes that cloaking small objects could have a range of applications in fields such as biomedical science.

The findings were published on Jan. 25 in the New Journal of Physics.

Click on the link to see the original article, Experimental verification of three-dimensional plasmonic cloaking in free-space.

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