all light stories

Light and matter united

Wed, 11 Jul 2007 12:04:48 -0400

Lene Hau has already shaken scientists' beliefs about the nature of things. Albert Einstein and just about every other physicist insisted that light travels 186,000 miles a second in free space, and that it can't be speeded-up or slowed down. But in 1998, Hau, for the first time in history, slowed light to 38 miles an hour, about the speed of rush-hour traffic.

Two years later, she brought light to a complete halt in a cloud of ultracold atoms. Next, she restarted the stalled light without changing any of its characteristics, and sent it on its way. These highly successful experiments brought her a tenured professorship at Harvard University and a $500,000 MacArthur Foundation award to spend as she pleased.

There's more to the North Star than meets the eye

70652986 — Mon, 26 Mar 2007 06:24:03 -0400

We tend to think of the North Star, Polaris, as a steady, solitary point of light that guided sailors in ages past. But there is more to the North Star than meets the eye - two faint stellar companions. The North Star is actually a triple star system. And while one companion can be seen easily through small telescopes, the other hugs Polaris so tightly that it has never been seen directly - until now.

By stretching the capabilities of NASA's Hubble Space Telescope to the limit, astronomers have photographed the close companion of Polaris for the first time. They presented their findings Jan. 9, 2006 in a press conference at the 207th meeting of the American Astronomical Society in Washington, D.C.

"The star we observed is so close to Polaris that we needed every available bit of Hubble's resolution to see it," said Smithsonian astronomer Nancy Evans (Harvard-Smithsonian Center for Astrophysics).

The companion proved to be less than two-tenths of an arcsecond from Polaris - an incredibly tiny angle equivalent to the apparent diameter of a quarter located 19 miles away. At the system's distance of 430 light-years, that translates into a physical separation of about 2 billion miles.

"The brightness difference between the two stars made it even more difficult to resolve them," stated Howard Bond of the Space Telescope Science Institute (STScI). Polaris is a supergiant more than two thousand times brighter than the Sun, while its companion is a main-sequence star. "With Hubble, we've pulled the North Star's companion out of the shadows and into the spotlight."

By watching the motion of the companion star, Evans and her colleagues expect to learn not only the stars' orbits but also their masses. Measuring the mass of a star is one of the most difficult tasks facing stellar astronomers.

Robotic telescope penetrates heart of universe's most powerful explosion

70652986 — Mon, 26 Mar 2007 06:18:25 -0400

Cullen Blake, a graduate student at the Harvard-Smithsonian Center for Astrophysics and lead author on the paper, said that the simultaneous observation of infrared light with a gamma-ray burst was unprecedented.

This observation was made possible by PAIRITEL's ability to aim at objects quickly and automatically. PAIRITEL pointed at the burst minutes after the Integral gamma-ray satellite detected it. PAIRITEL's efficiency allowed astronomers to spot infrared light from the explosion during the gamma-ray burst.

Have light, will not travel

70652986 — Mon, 26 Mar 2007 05:33:33 -0400

Harvard researchers fired a short signal pulse of red laser light into a sealed glass cylinder containing a hot gas of rubidium atoms illuminated by a strong control beam. While the pulse was traveling through the rubidium gas, they switched off the control beam, resulting in the storage of a holographic imprint of the signal pulse on the rubidium atoms. Instead of using a single control beam to re-create and release the signal pulse, as was done in earlier experiments, the Harvard team used two counterpropagating control beams. Besides re-creating the signal pulse, the two control beams generate a standing-wave pattern of dark and bright regions. This light pattern makes the atoms behave like a stack of tiny mirrors. As the re-created signal pulse tries to propagate through this medium, the photons bounce back and forth in such a way that the overall pulse remains frozen in space. The pulse can be released again by switching off one of the control beams. The present work may yield new approaches to enhance interaction between faint light pulses, which could help process information carried by light pulses. An example of this would be quantum information processing - a powerful theoretical approach that uses single photons' or atoms' quantum states to store information.

Light propagates via wires more slender than its own wavelength

70652986 — Mon, 26 Mar 2007 05:33:37 -0400

A research team led by Harvard's Eric Mazur and Limin Tong, a visiting professor from Zhejiang University in China, reported on their work with nanowires in the Dec. 18, 2003 issue of the journal Nature. "You wouldn't normally imagine that a baseball could pass through a garden hose, but these nanowires appear able to handle exactly that kind of wide load," says Mazur, Harvard College professor, Gordon McKay Professor of Applied Physics, and professor of physics. "In some cases light is propagating along wires just one-third the width of its own wavelength. It's almost as if the wire serves as a rail to guide the light rather than funneling it in the traditional sense." The wires could aid in the development of optical chips that operate more rapidly and efficiently than today's electronic chips. The tiny structures could also be used to manipulate cells and other microscopic objects. The wires are so fine that they could poke into a cell or a droplet of liquid without disrupting them, yet are extremely sturdy - several times stronger than spider silk, one of the gold standards in the world of materials.

Blue light special

70652986 — Mon, 26 Mar 2007 05:31:40 -0400

Jet-setters and shift workers now sit in front of glaring white lights to readjust their body rhythms and avoid sleep and alertness problems. New experiments condcuted by Harvard University researchers suggest that they would be better off sitting in front of blue lights. The research also contradicts what many scientists believed for years, that the 24-hour biological clock is set by sight alone. Until 1995, dogma held that the intensity of light striking receptors that give humans color vision also adjust the daily cycle that controls sleep, performance, and other physical and behavioral factors. Now, there is conclusive evidence for a second system that dominates the setting of daily rhythms in creatures from bacteria to international travelers, even blind ones. "The visual system in humans is most sensitive to green light," notes Steven Lockley of Brigham and Women's Hospital, a Harvard research and teaching affiliate. "But when we exposed 12 healthy young men and women to the same amount of either green or blue light, their 24-hour rhythms shifted twice as much with blue than with green."

New, far-out planet is discovered

70652986 — Mon, 26 Mar 2007 05:26:46 -0400

A planet discovered in the constellation Sagittarius is so distant that light takes 5,000 years to travel from there to here at a speed of 186,000 miles per second. Called OGLE-TR-56b, the planet orbits too close to its sun to be hospitable to living things. The way it was found could lead to the discovery of more planets like our lively Earth. "We have found a better way to detect new worlds in our own Milky Way galaxy, which makes future planetary discoveries easier," says Dimitar Sasselov, Thomas D. Cabot Associate Professor of Astronomy at the Harvard-Smithsonian Center for Astrophysics. Astronomers can't see such planets directly, even with the most powerful telescopes. They are too small compared with the stars they orbit, and they generate no light of their own.

Light illuminates better teaching strategies

70652986 — Mon, 26 Mar 2007 05:05:30 -0400

"When students say something works, that's powerful," says Harvard Professor Richard Light, author of "Making the Most of College." Among his findings: • The widely held belief that colleges should admit talented students and then "get out of their way" is directly contrary to what students actually want; students report that some of their most meaningful college experiences involve those teachers and administrators who actively "get in their way" by offering advice, opportunities, and challenges.

Harvard researchers stop, restart, light

70652986 — Mon, 26 Mar 2007 05:04:31 -0400

Albert Einstein theorized that light cannot travel faster than 186,282 miles per second. But he never said it couldn't go slower. Lene Hau, a physics professor in the Faculty of Arts and Sciences at Harvard University, says Einstein would "probably be stunned" at the results of her recent experiments. Working in her laboratory at the Rowland Institute for Science, she and her colleagues slowed light 20 million-fold in 1999, to an incredible 38 miles an hour. They did it by passing a beam of light through a small cloud of atoms cooled to temperatures a billion times colder than those in the spaces between stars. Just recently, they were able to stop light completely. "In this odd state, light takes on a more human dimension; you can almost touch it," Hau says.

Treating advanced lung cancer with light

70652986 — Mon, 26 Mar 2007 05:08:34 -0400

Photodynamic, or light, therapy was approved by the Food and Drug Administration in December 1998. The FDA has also approved using lasers for treatment of advanced stages of cancer of the esophagus. A surgeon can use lasers to shrink a tumor blocking an esophagus in about 15 minutes, as opposed to a five-hour operation to remove it by surgery. The light treatment saves the esophagus and eliminates a need for tube feeding. "The purpose of photodynamic therapy is not to cure anyone," says surgeon Ralph Bueno, who is an instructor in surgery at Harvard Medical School. "The majority of our patients are incurable. Their tumors cannot be reached by surgery, or treated successfully with radiation or chemotherapy.

Light weapons are most common in today's small wars

70652986 — Mon, 26 Mar 2007 05:10:15 -0400

In the 1990s, approximately 4 million soldiers and civilians were killed by small arms in the internecine conflicts of the developing world. More people, in other words, were killed in that decade in war by small arms than by major weapon systems, according to a Harvard research report. Likewise, millions have been wounded, displaced from their homes, and reduced to hunger by civil wars fueled by small arms. Economic development efforts have been undermined, medical costs increased, and improvements to living standards denied. The easy availability of small arms assists drug trafficking, terrorism, organized crime, and much more. Portable, cheap, and readily procured, small arms are supremely destructive. A Brazilian-made assault rifle can fire 700 rounds a minute. It is estimated that as many as 500 million small arms may currently be in circulation in the developing world.