New Invisibility Cloak Hides Objects from Human View

New Invisibility Cloak Hides Objects from Human View

  2:26:00 PM    Science Lover

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For the first time, scientists have devised an invisibility cloak material that hides objects from detection using light that is visible to humans. The new device is a leap forward in cloaking materials, according to a report in the ACS journal Nano Letters.

A real-life invisibility cloak, shown in this cross- sectional 
illustration, can hide objects from human view. (Credit: ACS)

Xiang Zhang and colleagues note that invisibility cloaks, which route electromagnetic waves around an object to make it undetectable, "are still in their infancy." Most cloaks are made of materials that can only hide things using microwave or infrared waves, which are just below the threshold of human vision. To remedy this, the researchers built a reflective "carpet cloak" out of layers of silicon oxide and silicon nitride etched in a special pattern. The carpet cloak works by concealing an object under the layers, and bending light waves away from the bump that the object makes, so that the cloak appears flat and smooth like a normal mirror.

Although the study cloaked a microscopic object roughly the diameter of a red blood cell, the device demonstrates that it may be "capable of cloaking any object underneath a reflective carpet layer. In contrast to the previous demonstrations that were limited to infrared light, this work makes actual invisibility for the light seen by the human eye possible," the scientists write.



The authors acknowledge funding from the U.S. Army Research Office, the Natural Sciences and Engineering Research Council of Canada, and the NSF Graduate Research Fellowship Program.

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Some People Talk About Space-Time Invisibility Cloaks. At Cornell, They Built One

Some People Talk About Space-Time Invisibility Cloaks. At Cornell, They Built One

  7:39:00 PM    Science Lover

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Physicists have created a "hole in time" using the temporal equivalent of an invisibility cloak.

A Temporal 'Time Cloak' Envisioned Moti 

Fridman et al. via arXiv

We’ve written previously about the theoretical possibility of “event cloaks” metamaterial space-time devices that could theoretically conceal an entire event in time from the view of an outsider. Well, while some bright minds were just talking about bending space-time to their whims, a team at Cornell was doing it. And it works. For 110 nanoseconds.

There’s a more thorough explanation of this notion in our previous coverage, but briefly this is the idea: basically, you need two time-lenses--lenses that can compress and decompress light in time. This is actually possible to do using an electro-optic modulator (what, you don’t have one?). Basically, using two of these modulators you would slow down or compress the light traveling through the first lens, and then set up a second lens downrange from the first that would decompress, or accelerate, the incoming photons from the first lens.

Got that? Refer to this handy gif, courtesy of some blokes working on a similar idea at Imperial College London:

Paul Kinsler, Imperial College London

Think of the photons like steadily flowing traffic on a highway. If you slow the traffic at a point upstream, you create a gap. You can cross the highway through the gap and then accelerate that traffic to catch up to the traffic ahead, closing the gap. To someone further downstream, the gap is not there--to that observer, the gap might as well have never existed because there’s no evidence of it.

During that gap, whatever occurs goes unrecorded. But, as we noted above, you’d have to be pretty quick were you to use such a device to pull some kind of shenanigans. The current device the Cornell gents have built creates a 110 nanosecond event gap, and they concede that the best it could achieve is 120 microseconds. But, as KFC notes at Technology Review, rarely is anything final in cutting edge theoretical physics.

Ref: arxiv.org/abs/1107.2062: Demonstration Of Temporal Cloaking

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