What’s the News: Lytro, a Silicon Valley start-up, has designed a camera that lets you shoot first and focus later. The camera captures the far more light and data than traditional models, and comes with software that lets you focus the photo, shift perspective, or go 3D after you’ve taken the photo. The company plans to sell a consumer, fits-in-your-pocket model by the end of the year.
Posts Tagged ‘light’
How To Build a Laser Tractor Beam (in Theory)
Light is pushy. The physical pressure of photons is what allows for solar sail space missions that ride on sunlight, and what allows for dreams of lasers that will push those sails even faster. And light can trap objects, too: Optical tweezers can hold tiny objects in place. Pulling an object with light, however, is another matter. Though it’s counter-intuitive to think you could create backward-tugging force with a forward propagating laser and create a real-life tractor beam, the authors of a new physics paper write that they have shown a way it could be done.
Jun Chen’s research team says that the key is to use not a regular laser beam, but instead what’s called a Bessel beam. Viewed head-on, a Bessel beam looks like one intense point surrounded by concentric circles—what you might see when you toss a stone into a lake. The central point in a Bessel beam suffers much less diffraction than a standard laser, and so scientists can use them for precision operations like punching a hole in a cell.
If such a Bessel beam were to encounter an object not head-on but at a glancing angle, the backward force can be stimulated. As the atoms or molecules of the target absorb and re-radiate the incoming light, the fraction re-radiated forward along the beam direction can interfere and give the object a “push” back toward the source. [BBC News]
Using Tiny Glass Spheres as a Superlens, Microscope Shatters Resolution Record
Modern microscopes opened up the world of the minute to an amazing degree, allowing people to see all the way down to a bacterium wriggling on a slide. But if you want to see down even smaller in regular optical light—to a virus, a cell’s interior, or other objects on the nanoscale—you’ve been out of luck. Those objects are smaller than 200 nanometers, what’s been considered the resolution limit for microscopes scanning in white light, and so the only was to see them was through indirect imaging devices like scanning electron microscopes.
Not anymore. Lin Li and colleagues report a new way using tiny beads to resolve images at 50 nanometers, shattering the limit for what can be seen in optical light.
Their technique, reported in Nature Communications, makes use of “evanescent waves“, emitted very near an object and usually lost altogether. Instead, the beads gather the light and re-focus it, channelling it into a standard microscope. This allowed researchers to see with their own eyes a level of detail that is normally restricted to indirect methods such as atomic force microscopy or scanning electron microscopy. [BBC News]
Those beads are called microspheres—they’re tiny glass balls about the size of red blood cells. The researchers apply these spheres to the surface of the object they want to see. In essence, the spheres capture light that normally would be lost before it ever reached the observer’s eye (those evanescent waves), enabling Li’s team to overcome the diffraction limits of microscope machinery that have limited the maximum possible resolution.
Scientists Create the World’s First Anti-Laser
The anti-laser—a tech with such a cool name it doesn’t need an obvious application—first came to our attention last year when Yale’s A. Douglas Stone proposed the idea. Now Stone is back with the real thing. His new paper in Science documents the world’s first anti-laser.
Conventional lasers create intense beams of light by stimulating atoms to spit out a coherent beam of light in which all the light waves march in lockstep. The crests of one wave match the crests of all the others, and troughs match up with troughs. The anti-laser does the reverse: Two perfect beams of laser light go in, and are completely absorbed. [Wired]
Anti-lasers are a bit of a funny concept, because anybody who has worn black on an August afternoon knows that absorbing light and turning it into heat isn’t a problem. But creating a device that matches the concentrated beam of a laser and traps more than 99 percent of it—essentially reversing a laser—is an engineering feat.
Whereas a laser uses mirrors to bounce light back and forth through an amplifying material to concentrate it, the anti-laser, as the name would suggest, does basically the opposite.
The Sight of Twisted Light Could Reveal a Spinning Black Hole
No, you can’t see a black hole. What you might be able to see, though, is the way in which relativity predicts a spinning black hole will bend space, time, and light around it. Scientists say in a new study in Nature Physics that they are closer than ever to being able to see this effect in faraway black holes from our vantage point here on Earth.
Galaxies probably have spinning, supermassive black holes at their center, and spinning black holes possess two types of angular momentum, study coauthor Bo Thide explains. There’s spin angular momentum, which is analogous to what the Earth creates as it spins on its axis, and there’s orbital angular momentum, which is analogous to what the Earth creates as it orbits the sun. Thidé says that the second effect—orbital angular momentum—distorts light in a way that scientists who know what to look for might be able to see it from here.
“Around a spinning black hole, space and time behave in such an odd way; space becomes time, time becomes space, and the whole space-time is actually dragged around the black hole, becomes twisted around the black hole,” Professor Thidé explained. “If you have radiation source… it will then sense this twisting of spacetime itself. The light ray may think that ‘I’m propagating in a straight line’, but if you look at it from the outside, you see it’s propagating along a spiral line. That’s relativity for you.” [BBC News]
Zap! I Sunk Your Battle Ship… With a Laser
Weapons-grade lasers still sound like the stuff of science fiction, but thanks to a major breakthrough by researchers at the Los Alamos National Lab in New Mexico, the Navy has taken a big step toward making this bit of sci-fi real. With the Free Electron Laser (FEL) program, the Navy hopes to use laser beams to blast enemies out of the sea and sky, and for the first time, they’re starting to generate enough power to do so, with the newfound ability to create a megawatt-level laser beam.
“The injector performed as we predicted all along,” said Dr. Dinh Nguyen, senior project leader for the FEL program at the lab. “But until now, we didn’t have the evidence to support our models. We were so happy to see our design, fabrication and testing efforts finally come to fruition. We’re currently working to measure the properties of the continuous electron beams, and hope to set a world record for the average current of electrons.” [Office of Naval Research]
Maneuvering on a Light Beam: How to Steer a Solar Sail Spacecraft
This summer, Japan’s golden solar sail unfurled in space, becoming the first successful mission to sail on the physical pressure of the sun’s radiation. Its success led dreamers like Planetary Society director Bill Nye to envision a future of machines pushed forward by the pressure of lasers to explore the cosmos. And now, down here on Earth, researchers say they have demonstrated one of the key principles needed to realize such a vision: a “lightfoil” that uses light to create lift.
The lightfoil described in Nature Photonics is only micrometers in scale, but lead researcher Grover Swartzlander argues that it shows scientists can create and control optical lift. It operates on the property of refraction–how glass bends light.
Optical lift is different from the aerodynamic lift created by an airfoil. A plane flies because air flowing more slowly under its wing exerts more pressure than the faster-moving air flowing above. But in a lightfoil, the lift is created inside the object as the beam shines through. The shape of the transparent lightfoil causes light to be refracted differently depending on where it goes through, which causes a corresponding bending of the beam’s momentum that creates lift. [Science News]
This neat trick could potentially be used to steer a spacecraft, the researchers say.
Peeping Tom Camera Uses Lasers to Peer Around Corners
A new camera being developed at MIT has the ability to see around corners–without the use of periscopes or mirrors.
The camera works by bouncing ultra-short bursts of laser light off a solid surface (like a floor or an open door). Most of the light is reflected back to the camera, but some scatters in every direction, a small portion of which then hits and bounces off the object to be visualized (and other parts of the scene). Some of that scattered light then bounces back off the door or floor, and finally make its way back to the camera.
“It’s like having x-ray vision without the x-rays,” said Professor Ramesh Raskar, head of the Camera Culture group at the MIT Media Lab and one of the team behind the system. “But we’re going around the problem rather than going through it.” [BBC News]
The team’s computer program can analyze the scattered light and re-create a picture of what is lurking around the corner. The secret to the technology is to not overwhelm the camera’s sensors with the initial reflection from the door. The camera’s shutter has to wait until this initial pulse has passed before trying to collect the light bouncing around.
The camera notes the arrival time and intensity of each photon of light to build a three dimensional picture of what it can’t actually see. It takes several passes of the scene to build a full picture.
(more…)
4D Invisibility Cloak Bends Time as Well as Space
First came the formulation of an invisibility cloak that could bend light around an object. Then, this spring, German scientists took that idea and made it three-dimensional. Is the invisibility cloak now ready to go 4D? For a study in the Journal of Optics, British researcher Martin McCall’s team adds the dimension of time to the invisibility cloak idea, creating a theoretical “space-time cloak.”
The key feature of the proposed space–time cloak is that its refractive index — the optical property that governs the speed of light within a material — is continually changed, pulling light rays apart in time. When the leading edge of a light wave hits the cloak, the material is manipulated to speed up the light, but when the trailing edge hits, the light is slowed down and delayed. “Between these two parts of the light, there will be a temporal void — a space in which there will be no illuminating light for a brief period of time,” explains McCall. [Nature]
Taking advantage of these differences, he says, it is theoretically possible to imagine a cloak that allows you—at least from my point of view—to transport instantaneously across space.
Pretty Liquid Crystal Experiments Could Reorganize Electronic Displays
A new approach to electrophoresis is giving researchers more control over how they play with small particles.
Electrophoresis is the movement of particles in solution under a current–a phenomenon that can be exploited for use in everything from ePaper to DNA separating gels. Instead of using a normal fluid to conduct current, researchers led by Oleg Lavrentovich tried using liquid crystals as their conductive fluid.
Liquid crystals, like those seen in the first three pictures above (which might look similar to the patterns you’ve seen when you push on the screen of some of your electronics), act like a fluid. But instead of being a disorganized jumble of molecules, the individual rod-shaped particles line up parallel to each other. When they take on different orientations, they refract different colors of light, a phenomenon called birefringence.
Implantable LEDs Could Be Medical Sensors, or Sweet Glowing Tattoos
Flexible materials technology may just bring the next wave of trendy to the markets, in the form of glowing tattoos and T- shirts. Or the hot new tech could be used for its intended purpose: monitoring medical conditions.
This flexible light-emitting diode (LED) array uses many already existing materials and techniques to create a nano-sized, flexible patch of light. A team lead by John Rogers developed the array as a medical device; it could be implanted to serve as a readout for monitoring internal body conditions, like blood oxygenation or glucose levels, or it could turn on light-activated drugs.
“The applications we’re interested in mostly include interfaces with the human body,” says John Rogers…. For some biological applications, he adds, a conventional LED’s brightness, reliable operation and suitability for waterproof implementation make it a more attractive option than an organic LED. [Scientific American].
Each individual LED is a square that measures 2.5 micrometers thick (smaller than the diameter of your cells’ nucleus) and 100 micrometers on each side (the thickness of a coat of paint). Many of these LEDs can be printed together to form an array of light points connected by swirls of connective wire that give it additional flexibility. The substrate is flexible enough that it can be stretched and flexed up to 75 percent without losing function. The researchers described the technology in the journal Nature Materials.
Quasar Study Suggests a Physics Constant Isn’t so Constant
After analyzing light coming from distant quasars, some researchers have asked a physical constant a blunt question: Are you really constant at all? And since the “fine structure constant” that they’re interrogating is important for how physicists understand things like electrons’ behavior in atoms and fusion in stars, other physicists are asking their own question: Are your measurements correct?
The paper, which appeared last month in arXiv, argues that the constant might vary depending on location. This controversial claim is a new twist on a previous controversial claim–made over the past decade by some of the same physicists–which said that the constant varied with time.
Craig Hogan of the University of Chicago and the Fermi National Accelerator Laboratory in Batavia, Ill., acknowledges that “it’s a competent team and a thorough analysis.” But because the work has such profound implications for physics and requires such a high level of precision measurements, “it needs more proof before we’ll believe it.” [Science News]
Could Infrared-Loving Chlorophyll Let Solar Cells Capture More Energy?
After mashing up rock and algae chunks known as stromatolites, researchers have found a new type of chlorophyll, the pigment in plants that takes in light and provides energy for photosynthesis. Unlike its known cousins, this chlorophyll uses infrared light–that’s a surprise to some researchers, who doubted that lower frequency infrared had enough energy to split water for photosynthesis’s oxygen-creation.
“Nobody thought that oxygen-generating organisms were capable of using infrared light… ,” says Samuel Beale, a molecular biologist at Brown University whose work centers in part on chlorophylls [but who was not involved with the study]. “I think what they found here is a new modification of chlorophyll that shows the flexibility of photosynthetic organisms to use whatever light is available.” [Scientific American]
Researchers Use Lasers to Control the Beating of a Heart
In early 2010, some scientists offered their predictions for the new decade which this blog covered in the post, “Scientists Predict: The 2010s Will Be Freakin’ Awesome–With Lasers.” In what could be an early sign of that sunny prognostication coming true, researchers have announced that they’ve controlled the beating of an embryonic heart with an infrared laser beam. While the work is in its early stages, researchers say this remarkable advance will help them study heart disease and could one day lead to optical pacemakers.
The embryonic hearts in question came from quail eggs. Each quail embryo was only two or three days old so the heart measured just 2 cubic millimeters in volume; at that stage, the heart is essentially a clump of cells that hasn’t yet developed its four-chambered structure. The pulses of infrared light were delivered by an optical fiber that ended 500 micrometres from the embryo.
Before they switched on the laser, the heart beat once every 1.5 seconds, but firing the laser twice a second quickened the heartbeat to match the laser rate as long as the laser fired…. ”It worked beautifully: the heart rate was in lockstep with the laser pulse rate,” says [study coauthor] Duco Jansen of Vanderbilt University in Nashville, Tennessee. [New Scientist]
“Anti-Laser” Would Absorb the Light a Laser Shoots out
Sure, a laser can shine finely-tuned light to do anything from scanning your barcodes to correcting your vision, but soon that precise hero may meet its match: Physicists have recently imagined a device that can absorb light of certain frequencies, an “anti-laser.”
Absorbing light may not seem all that impressive, since after all, anything that appears black works as an absorber. Your driveway, however, is not the anti-laser. A paper in the Physical Review Letters lays out the plans for this device which can absorb light wave clones (same frequency, phase, and polarization) that some lasers emit. The pickiness of this theoretical light absorber is part of what would make the device unique, just as an important part of what separates a laser from a flashlight is the precision of the light a laser emits.
Instead of amplifying light into coherent pulses, as a laser does, an antilaser absorbs light beams zapped into it. It can be “tuned” to work at specific wavelengths of light, allowing researchers to turn a dial and cause the device to start and then stop absorbing light. “By just tinkering with the phases of the beams, magically it turns ‘black’ in this narrow wavelength range,” says team member A. Douglas Stone, a physicist at Yale University. “It’s an amazing trick.” [Science News]
