‘Cloaking’ device uses ordinary lenses to hide objects across range of angles : NewsCenter

‘Cloaking’ device uses ordinary lenses to hide objects across range of angles : NewsCenter: “This is the first device that we know of that can do three-dimensional, continuously multidirectional cloaking, which works for transmitting rays in the visible spectrum..."

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.

Lasers make fibre optic tubes out of thin air - tech - 22 July 2014 - New Scientist

Lasers make fibre optic tubes out of thin air - tech - 22 July 2014 - New Scientist: The team shone four lasers in a square arrangement, heating air molecules and creating a low-density ring around a denser core of air. Light bounces around the dense core just like in a fibre.

The air fibre lasts for a few milliseconds – more than enough to send a signal.

How to Build an Evryscope | MIT Technology Review

How to Build an Evryscope | MIT Technology Review: Their new gigapixel-scale telescope will be capable of photographing the entire sky simultaneously and continuously at relatively low cost...

It consists of 23 small telescopes mounted on a hemispherical dome that can rotate to track the sky. Each small telescope has a 7 cm aperture and a field of view of a few hundred square degrees. Each one focuses light onto 29 megapixel chip.

The dome is designed so that the fields of view of each of the small telescopes overlap to cover around 10,000 square degrees of sky simultaneously and to produce 0.7 gigapixel images. The dome rotates on equatorial mount so that the Evryscope can record exposures of up to 3 hours before ratcheting back and tracking the next sky area.

Hollow optical fibers for UV light

Hollow optical fibers for UV light: Researchers... have tested a new type of optical fibre with a hollow core and have found out that this type of optical fibre was able to guide UV laser light without being damaged and with acceptable loss.

New ultrastiff, ultralight material developed | MIT News Office

New ultrastiff, ultralight material developed | MIT News Office: The actual production of such materials is made possible by a high-precision 3-D printing process called projection microstereolithography...

“We found that for a material as light and sparse as aerogel [a kind of glass foam], we see a mechanical stiffness that’s comparable to that of solid rubber, and 400 times stronger than a counterpart of similar density. Such samples can easily withstand a load of more than 160,000 times their own weight,” says Fang...

New ‘switch’ could power quantum computing | MIT News Office

New ‘switch’ could power quantum computing | MIT News Office:  “We have demonstrated basically an atom can switch the phase of a photon. And the photon can switch the phase of an atom...”

In this case, the researchers used a laser to place a rubidium atom very close to the surface of a photonic crystal cavity, a structure of light. The atoms were placed no more than 100 or 200 nanometers — less than a wavelength of light — from the edge of the cavity. At such small distances, there is a strong attractive force between the atom and the surface of the light field, which the researchers used to trap the atom in place...

“In some sense, it was a big surprise how simple this solution was compared to the different techniques you might envision of getting the atoms there,” Vuletić says.

Curved Spacetime Mimicked on a Chip: Scientific American

Curved Spacetime Mimicked on a Chip: Scientific American: Liu and his collaborators simulated the gravitational lensing of a star on an integrated photonic chip. A layer of clear plastic on the chip acted as a waveguide, confining light to the chip’s surface. To change the index of refraction of the plastic, the researchers had to vary the plastic’s thickness. They did so by heating the plastic and adding polystyrene microspheres before the plastic cooled. Because the plastic rose upwards around the microspheres on cooling, the thickness of the waveguide increased near these miniature balls. The varying index of refraction the team achieved happens to be very similar to the bending of space-time geometry around a massive star...

“This is indeed the first time an exact solution of Einstein's equations was mimicked” using an optical model, says Leonhardt.

Researchers slow light to a crawl in liquid crystal matrix

Researchers slow light to a crawl in liquid crystal matrix: The new approach... uses little power, does not require an external electrical field, and operates at room temperature, making it more practical than many other slow light experiments...


The key to achieving a significant drop-off in speed is to take advantage of the fact that when light travels as a pulse it is really a collection of waves, each having a slightly different frequency, says Bortolozzo. However, all the waves in the pulse must travel together. Scientists can design materials to be like obstacles courses that "trip up" some of the waves more than others. In order to exit the material together, the pulse must wait until it can reconstitute itself...


They added a chemical component that twisted the liquid crystal molecules into a helical shape and then added dye molecules that nestled in the helical structures. The dye molecules change their shape when irradiated by light, altering the optical properties of the material and hence changing the relative velocities of the different wave components of the light pulse as it travelled through. In addition, the helical structure of the liquid crystal matrix ensures a long lifetime of the shape-shifted dyes, which makes it possible to "store" a light pulse in the medium and later release it on demand...

Physicists freeze motion of light for a minute

Physicists freeze motion of light for a minute: To stop the light, the physicists used a glass-like crystal that contains a low concentration of ions – electrically charged atoms – of the element praseodymium. The experimental setup also includes two laser beams. One is part of the deceleration unit, while the other is to be stopped. The first light beam, called the "control beam", changes the optical properties of the crystal: the ions then change the speed of light to a high degree. The second beam, the one to be stopped, now comes into contact with this new medium of crystal and laser light and is slowed down within it. When the physicists switch off the control beam at the same moment that the other beam is within the crystal, the decelerated beam comes to a stop.


More precisely, the light turns into a kind of wave trapped in the crystal lattice. This can be explained in greatly simplified form as follows. The praseodymium ions are orbited by electrons. These behave similarly to a chain of magnets: if you put one into motion, the movement – mediated by magnetic forces – propagates in the chain like a wave. Since physicists call the magnetism of electrons "spin", a "spin wave" forms in the same manner when freezing the laser beam. This is a reflection of the laser's light wave. In this way, the Darmstadt researchers were able to store images, such as a striped pattern, made of laser light within the crystal. The information can be read out again by turning the control laser beam on again.

Researchers find way to measure speed of spinning object using light's orbital angular momentum

Researchers find way to measure speed of spinning object using light's orbital angular momentum: In this new effort, the researchers found a way to measure the spin speed of an object that is not observed at an angle by taking advantage of a characteristic of light known as orbital angular momentum (OAM). This is where electromagnetic energy associated with light flows forward in the direction of propagation while also continuously moving around its own axis. In essence, it's light moving through space like a corkscrew. The researchers found that light can be imbued with OAM if it is reflected off a rotating object and it was this discovery that led to its use in calculating the spin speed of the object. Specifically, they found they could calculate the spin speed of the object by measuring the OAM in the light that has been reflected back by it.

To test their theory, the researchers fired a laser at a spinning plate in their lab then used a light detector to measure the degree of OAM. Because the plate was spinning, it gave off both positive and negative OAM—the degree of difference between the two gave the researchers the speed of rotation of the object.

Time cloak hides events by splicing them movie style

Time cloak hides events by splicing them movie style: Time cloaks work by slowing down light in an optical fibre, creating a gap in the beam. Any outside light that enters the hole becomes cloaked when the original beam is sped up...

A diffraction grating stretches out a laser beam, producing a series of gaps. Pulses of light sent along the fibre at the same time slot into these. A second grating then closes the holes, hiding the pulses from the intended receiver. There is now no record that the pulses ever traversed the fibre... This string of cloaks can hide up to 1.5 gigabytes per second.

BBC News - Invisibility cloaking in 'perfect' demonstration

BBC News - Invisibility cloaking in 'perfect' demonstration: So someone would not see a cloaked object but rather the scene behind it - however, the reflections from the cloak would make that scene appear somewhat darkened.

Now, Prof Smith and his Duke colleague Nathan Landy have taken another tack, reworking how the edges of a microwave cloak line up, ensuring that the light passes around the cloak completely with no reflections.

The trick was to use a diamond-shaped cloak, with properties carefully matched at the diamond's corners, to shuttle light perfectly around a cylinder 7.5cm in diameter and 1cm tall.

Nanoscale Device Makes Light Travel Infinitely Fast - ScienceNOW

Nanoscale Device Makes Light Travel Infinitely Fast - ScienceNOW: They've developed a tiny device in which the index of refraction for visible light is zero—so that light waves of a particular wavelength move infinitely fast.

The device consists of a rectangular bar of insulating silicon dioxide 85 nanometers thick and 2000 nanometers long surrounded by conducing silver, which light generally doesn't penetrate. The result is a light-conveying chamber called a waveguide. Researchers fashioned different devices in which the width of the silicon dioxide ranged from 120 to 400 nanometers...

Right at the cutoff wavelength, things get interesting. Instead of producing a banded pattern, the whole waveguide lights up. That means that instead of acting as waves with equally spaced peaks, or "phase fronts," the wave behaves as if its peaks are moving infinitely fast and are everywhere at once. So the light oscillates in synchrony along the length of the waveguide.

Flat lens offers a perfect image — Harvard School of Engineering and Applied Sciences

Flat lens offers a perfect image — Harvard School of Engineering and Applied Sciences: At a mere 60 nanometers thick, the flat lens is essentially two-dimensional, yet its focusing power approaches the ultimate physical limit set by the laws of diffraction.

Operating at telecom wavelengths (i.e., the range commonly used in fiber-optic communications), the new device is completely scalable, from near-infrared to terahertz wavelengths, and simple to manufacture...


Capasso and his collaborators at SEAS create the flat lens by plating a very thin wafer of silicon with a nanometer-thin layer of gold. Next, they strip away parts of the gold layer to leave behind an array of V-shaped structures, evenly spaced in rows across the surface. When Capasso’s group shines a laser onto the flat lens, these structures act as nanoantennas that capture the incoming light and hold onto it briefly before releasing it again. Those delays, which are precisely tuned across the surface of the lens, change the direction of the light in the same way that a thick glass lens would, with an important distinction.

The flat lens eliminates optical aberrations such as the “fish-eye” effect that results from conventional wide-angle lenses...

How To Steer Sound Using Light - Technology Review

How To Steer Sound Using Light - Technology Review: Zap an optical fibre with a couple of laser beams and the resulting interference pattern causes an interesting effect--it squeezes the material, an effect known as electrostriction...
Not to be outdone, phonons also influence light because they change the refractive index of the material. This bends light and alters its frequency, an effect known as Brillouin scattering...
They say that the light ends up guiding the phonons that it creates. In other words, it's possible to create and then steer sound using light. "The phonon wavepacket generated via [electrostriction] is naturally guided by the light that gave it birth," say Beugnot and Laude.

An Invisibility Cloak With An On-Off Switch

An Invisibility Cloak With An On-Off Switch: What makes this possible is a process known as electromagnetically induced transparency--a phenomenon in which certain materials become transparent when zapped by light from two carefully tuned lasers...

If the frequencies of the lasers are close together, they can be tuned in a way that makes them interfere destructively. And when this happens, their ability to excite electrons cancels out.

When this happens, the laser photons suddenly pass through the material unimpeded, sometimes at dramatically reduced at speeds (which is how experiments that stop light are performed)...

Their trick is to use atoms that can exist in five electronic states rather than three. This allows additional control over the refractive index called magneto-electric cross-coupling.


The bottom line is that this allows an external magnetic field to modulate the change in refractive index.

How To Build A Maxwell's Fishpond

How To Build A Maxwell's Fishpond: One mathematical solution stuck out as being particularly special: a lens in which all rays of light follow circular arcs. In this lens, light from any point in or on the sphere is always focused to another point on the other side of the sphere...
These guys have built a two dimensional version of Maxwell's fisheye lens which works with water waves rather than electromagnetic ones. Naturally, they call their device a Maxwell's fishpond.
The device is remarkably simply--a shallow dish with a curved bottom that rises towards the middle...When filled with water, waves on the surface behave in a remarkable way. The depth of the water determines the refractive index of waves on the surface. So the trick here is to design the shape of the bottom of the dish in a way that follows Maxwell's plan.
That turns out to be pretty straightforward with the result that a circular wave pattern does not simply spread out and disperse. Instead, it always reconverges to a point on the other side of the dish, regardless of where it formed in the first place.

Chinese Physicists Smash Distance Record For Teleportation

Chinese Physicists Smash Distance Record For Teleportation: Juan Yin at the University of Science and Technology of China in Shanghai, and a bunch of mates say they have teleported entangled photons over a distance of 97 kilometres across a lake in China...


So the most important advance these guys have made is to develop a steering mechanism using a guide laser that keeps the beam precisely on target. As a result, they were able to teleport more than 1100 photons in 4 hours over a distance of 97 kilometres.

That's interesting because it's the same channel attenuation that you'd have to cope with when beaming photons to a satellite with, say, 20 centimetre optics orbiting at about 500 kilometres. "The successful quantum teleportation over such channel losses in combination with our high-frequency and high-accuracy [aiming] technique show the feasibility of satellite-based ultra-long-distance quantum teleportation," say Juan and co.

Gamma-Ray Bending Opens New Door for Optics

Gamma-Ray Bending Opens New Door for Optics: Theory says that gamma rays, being even more energetic than x-rays, ought to bypass orbiting electrons altogether; materials should not bend them at all and the refractive index for gamma rays should be almost equal to one...

ILL is a research reactor that produces intense beams of neutrons. Habs, Jentschel, and colleagues used one of its beams to bombard samples of radioactive chlorine and gadolinium to produce gamma rays. They directed these down a 20-meter-long tube to a device known as a crystal spectrometer, which funneled the gamma rays into a specific direction. They then passed half of the gamma rays through a silicon prism and into another spectrometer to measure their final direction, while they directed the other half straight to the spectrometer unimpeded. To the researchers' surprise, as they report in a paper due to be published this month in Physical Review Letters, gamma rays with an energy above 700 kiloelectronvolts are slightly bent by the silicon prism...

So what drives this new bending effect? Although he can't be sure, Habs believes it resides in the nuclei at the heart of the silicon atoms. Although electrons don't normally reside in nuclei because of the very strong electric fields there, quantum mechanics allows pairs of "virtual" electrons and antielectrons, or positrons, to blink briefly into existence and then recombine and disappear again. Habs thinks the sheer number of these virtual electron-positron pairs amplifies the gamma-ray scattering, which is normally negligible, to a detectable amount.

Super-accurate atomic clock sets time travel record

Super-accurate atomic clock sets time travel record: Atomic clocks use precisely tuned electromagnetic waves to track the incredibly regular vibrations of atoms. Older atomic clocks tracked atoms that vibrate at microwave frequencies, while the latest generation use even faster optical frequencies. But while microwave clocks can be synchronised using satellite transmissions, these signals are too noisy for the more precise optical clocks...
The uncertainty in the frequency of the signal that arrived was just 4 x 10 -19 seconds, around 1000 times more accurate than signals transmitted by satellite methods...
Predehl suggests creating a network of optical clocks spread across the world.