By using simple, inexpensive, and readily available materials, researchers at at the University of Rochester have developed an optical system that can actually hide objects in the visible spectrum of light.
Cloaking devices are a kind of holy grail for physicists. The ability to hide objects from plain sight would be a remarkable achievement with applications ranging from medicine to the military. To date, efforts have been unwieldily, bizarre, and limited (i.e objects re-appear when gazed at from different angles). Sure, researchers have managed to hide certain wavelengths of light, but namely those in the part of the spectrum we can't see.
According to the researchers, the new device is the first to do three-dimensional, continuously multidirectional cloaking, which works for transmitting rays in the visible spectrum.
Now, while the new system developed by the University of Rochester researchers won't conceal you completely, it could eliminate blind spots in vehicles or let surgeons see through their hands during complex operations.
John Howell, a professor of physics at the University of Rochester, along with graduate student Joseph Choi, combined four standard optical lenses that keeps the object hidden, even as the viewer moves side to side.
From Rochester University:
Many cloaking designs work fine when you look at an object straight on, but if you move your viewpoint even a little, the object becomes visible, explains Howell. Choi added that previous cloaking devices can also cause the background to shift drastically, making it obvious that the cloaking device is present.
In order to both cloak an object and leave the background undisturbed, the researchers determined the lens type and power needed, as well as the precise distance to separate the four lenses. To test their device, they placed the cloaked object in front of a grid background. As they looked through the lenses and changed their viewing angle by moving from side to side, the grid shifted accordingly as if the cloaking device was not there. There was no discontinuity in the grid lines behind the cloaked object, compared to the background, and the grid sizes (magnification) matched.
The Rochester Cloak can be scaled up as large as the size of the lenses, allowing fairly large objects to be cloaked. And, unlike some other devices, it's broadband so it works for the whole visible spectrum of light, rather than only for specific frequencies.
Admittedly, the set up is not quite 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.
The cloaked region is essentially shaped like a doughnut, but the researchers have already built slightly more complicated designs that solve the problem.
Awesomely, the researchers say you can build your own "Rochester Cloak" by following these "simple" steps:
- 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 byt1= 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.
Read the scientific paper here. It's slated for publication in the journal Optics Express.
Credit: J. Adam Fenster / University of Rochester.