We all know about invisible cloak of Harry Potter which was a magical artifact and get fascinated. Now in science fiction, capes can make kids invisible, but in real life, scientists have only been able to hide certain wavelengths of light. But now, researchers at the University of Rochester have used simple, inexpensive, off-the-shelf components to hide objects in the visible spectrum of light.
Can we have real invisibility Cloaks
The Concept of cloaking is to manipulate light waves, forcing them around an object, like sending river water around a stone. Frequently, scientists use high-tech, exotic “meta-materials” that are expensive to develop, manipulate a part of the spectrum people can’t see anyway, or only work when one looks directly at the object. If you shift, you might see the object or the background shift around, giving away the trick.
This man-made material, called “meta-materials,” are tossing the laws of physics out the window. These materials have far-out capabilities, like bending sound and light around solid objects, and in some cases, making them invisible. Their behavior is not determined by individual atoms, but by larger artificial structures called meta-atoms.
“These meta-materials are revolutionary in concept,” said John Pendry, professor of theoretical solid state physics at Imperial College London.
Invisibility cloaks are one dreamy application. “Ten years ago we wouldn’t know how to make one,” said Steve Cummer, associate professor of electrical and computer engineering at Duke University. “Now we know what we have to do to make one.”
John Howell, a professor of physics at the University of Rochester, and graduate student Joseph Choi combined four standard optical lenses in a way that keeps the object hidden, even as the viewer moves side to side.
The video shows the effect.
Build your own Rochester Cloak
The researchers published their results in the journal Optics Express. They’ve also published a recipe for a do-it-yourself cloaking device at home. If you want to try it.
- Purchase 2 sets of 2 lenses with different focal lengths f1 and f2 (4 lenses total, 2 with f1 focal length, and 2 with f2 focal length)
- Separate the first 2 lenses by the sum of their focal lengths (So f1 lens is the first lens, f2 is the 2nd lens, and they are separated by t1= f1+ f2).
- Do the same in Step 2 for the other two lenses.
- Separate the two sets by t2=2 f2 (f1+ f2) / (f1— f2) apart, so that the two f2 lenses are t2 apart.
For their demonstration cloak, the researchers used 50mm achromatic doublets with focal lengths f1 = 200mm and f2 = 75mm. Credit: University of Rochester.
- Achromatic lenses provide the best image quality.
- Fresnel lenses can be used to reduce the total length (2t1+t2)
- Smaller total length should reduce edge effects and increase the range of angles.
- For an easier, but less ideal, cloak, you can try the 3 lens cloak in the paper.
At the moment, the set up is not perfect. “This cloak bends light and sends it through the center of the device, so the on-axis region cannot be blocked or cloaked,” said Choi. In essence, the cloaked region is shaped like a doughnut. But Choi and Howell have already built slightly more complicated designs that solve the problem.
Choi recently published a paper about some of the possibilities, and also demonstrated simple cloaking with mirrors, like magicians would use, in the above brief video.