While the country song by this title refers to tractors in an agricultural context, the tractor beam is actually a theoretical physics concept. This beam is said to draw particles toward its source instead of pushing them away. Since the theoretical existence of such a sci-fi-style beam was first proposed a few years back, most physicists have come to accept the concept, and many have been trying to prove its existence ever since.
Now researchers in the Czech Republic have built the first working example of this technology. Not only did their real-life tractor beam attract polystyrene particles, but the researchers were surprised to find it could also sort them.
What’s the News: Scientists have developed the first biological laser, made from a single living cell. This “living laser,” described in a new study in Nature Photonics, could one day lead to better medical imaging and light-based treatments for cancer or other diseases.
What’s the News: In a demonstration near California’s San Nicholas Island last Wednesday, scientists with the U.S. Navy tested a laser weapon aboard the USS Paul Foster by shooting a 15-kilowatt beam at an inflatable boat from a mile away, causing the outboard engines to burst into flames. It was the world’s first successful water-test of a high-energy laser. “I spent my life at sea,” Rear Adm. Nevin Carr told Wired, “and I never thought we’d see this kind of progress this quickly, where we’re approaching a decision of when we can put laser weapons on ships.”
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]
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.
With the space shuttles soon bound for retirement homes, NASA is dreaming up the future of U.S. human space flight. Recently, NASA has divulged its interest in two new gadgets: rockets launched via lasers and reusable, manned, deep-space crafts. Now, all the agency needs is a plan to get more money from the government to actually build these things.
The lasers (or possibly microwaves) would be ground-based, and would shoot through the air to energize a rocket’s heat exchanger; elevating the rocket’s fuel to over 3,100 degrees Fahrenheit would give it more thrust.
“The objective is to reduce the cost of getting into space. The way this rocket works, it has a more energetic propulsive system than one where you have fuel and oxidizer that release energy,” Carnegie Mellon University’s Kevin Parkin, head of the Microwave Thermal Rocket project at NASA’s Ames Research Center in California, told Discovery News. [Discovery News]
Although the laser-powered rocket system would be expensive to build, it would reduce launch costs in the long haul.
Taking advantage of the emerging technique of optogenetics, Harvard researchers report in the journal Nature Methods that they can target any individual neuron of the tiny transparent worm C. elegans, whether the creature is moving or at rest, and zap it with a laser to see what the particular cell does—move the worm to the left or right, or even cause it to lay eggs.
The whole process, from finding the cell to light hitting its target, takes about 20 milliseconds. As the worm’s position changes, that information is fed back into the computer program, and the laser is adjusted. If the worm crawls too far, a motorized microscope stage brings the animal back. One of the biggest benefits of the new method, [biologist William] Ryu says, is that it works in a roving animal. “The worms are not held down in any way — they’re freely moving. There aren’t many systems where you can look at such truly free organisms.” [Science News]
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.
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.