The core of the new room-temperature maser
When the laser was first invented, it was “a solution waiting for a problem,” a piece of cutting-edge technology with no applications. Today, found in everything from sensors to communications to surgery, the laser has come into its own—but it may be time to step aside and share the spotlight with its older brother, the maser.
Lasers and masers work on the same principle, amplifying light through a process called stimulated emission, except that lasers amplify visible light while masers act on microwaves. Light and microwaves are both forms of electromagnetic radiation, but microwaves have a wavelength 100,000 times greater than that of visible light. But although the maser has been used for deep-space communications and atomic clocks, lasers have always outshone their predecessors. And masers have only themselves to blame, as these finicky devices require extreme conditions like vacuum or cold temperatures. Now, however, researchers have finally produced a maser that functions while surrounded by air at room temperature.
The color you see is a perceptual trick of your brain: it is not, no matter what your preschool teacher told you, an inherent physical property of that red apple or green leaf. The truth is that colorful objects just happen to be reflecting wavelengths of light that our brains interpret as specific colors. Do we all see those reflected wavelengths the same way? Because the experience of color vision is impossible to share, we simply don’t know. It’s quite possible that they’re not. In fact, a certain subset of people may well see a hundred times as many colors of the rest of us, but, because of the essentially privateness of color vision, have never realized that they are different.
In a tour through recent research on the perception of color, Natalie Wolchover at Life’s Little Mysteries also turns up another weird insight to add to the long list of strange things about color vision: It could be the blueness of light around twilight that makes us calm, and the yellowness of light around dawn that wakes us up, rather than brightness and darkness:
In the presence of ultraviolet light, the nanoparticle
shrinks from 150 to 40 nanometers.
As anyone who has played with a powerful laser or just suffered a bad sunburn can attest, light has an impressive power to physically change objects. And now we know that light can make nanoparticles expand and contract like miniature Hoberman Spheres. MIT and Harvard researchers engineered nanoparticles that shrink to less than a third of their original size when exposed to ultraviolet rays; in the darkness or under visible light, they open back up to their more stable, larger size.
Nanoparticles have been touted as an effective way to deliver cancer-killing drugs straight to tumors without harming healthy cells in the process. But the structure of a tumor can block all but the smallest particles—those less than 100 nanometers (billionths of a meter)—from penetrating to the cancer’s heart. To deliver drugs to the entire tumor, the researchers suggest that the particles could be deployed while UV light keeps them in their smaller form, about 40 nanometers. Then, when the UV light is switched off, the particles will open to their full 150-nanometer size and release the drugs.
The ancestors of modern humans developed color vision 30 million years ago. But it was not until the late 1700s that there are records of anyone seeing colors in an unusual way. English chemist John Dalton, who found that people thought he was joking when he asked whether a geranium flower was blue or pink, wrote a description in 1794 of what he saw for the Manchester Literary and Philosophical Society journal: His world was suffused by shades of blue and yellow, but contained none of the mysterious sensation known as red. “That part of the image which others call red,” he wrote, “appears to me little more than a shade or defect of light.” It was one of the first mentions of colorblindness in human history.
In the centuries since, we have discovered what it is that robs some people of such sensations. Those of us with standard vision, called trichromats, have three kinds of pigments, or cones, in our retinae, each sensitive to a certain range of light and spaced out across the visible spectrum so that they can together convey to the brain everything from red to violet. In the colorblind, a mutated cone is so close to another in sensitivity that parts of the spectrum aren’t covered, or there are only two functioning cones, a condition called dichromacy. A difference of one cone causes a serious change in the number of discernable colors: Dichromats see on the order of 10,000 colors, trichromats on the order of a million. But that isn’t the end of the story. Recently, as genetic analyses and tests of color vision have grown more sophisticated, we are stumbling into one of the most curious discoveries in vision since Dalton’s day. Dichromats have 2 cones, trichromats have 3, tetrachromats have 4, making them theoretically capable of seeing 100 million colors.
The Raman spectrometer emits a laser beam.
What’s the News: Using a laser, a super-strong telescope, and some physics know-how, researchers say they have impressive power to look through solid barriers. Scientists have developed a technique to do so using Raman scattering, which is the change in energy of photons bouncing off a material. The technique could be used to detect hidden explosives or do geological analysis.
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.
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]
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.
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.
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]