Aug. 12, 1999 When you listen to music on your CD changer, or watch a movie on your DVD player, or run software on your PC's CD-ROM drive, this is what happens: A laser--a narrow beam of light--reads the surface of the disc, which has been encoded either to reflect the light back or to let it pass through. The resulting snippet of digital information, represented by a "0" or a "1," constitutes a fraction of a musical note, a blink of a car chase, a flash of an outfielder hauling in a long fly ball.
String enough of those tiny bits together, and you have an entire album, a whole movie, or a cool video baseball game.
It's amazing technology, but Temple University physicist Zameer Hasan doesn't think it goes far enough. He believes there is a way to fit much, much more material on a disc, and is shooting around lasers of his own, vaporizing solids, and studying the optical properties of solids to find a way to do so.
Hasan's field of research is known as solid-state optical physics, or optoelectronics. It offers mind-boggling possibilities for storing and retrieving data.
Hasan, a professor of physics, is using already existing technology that allows a laser beam to be split into an almost infinite variety of colors--billions of different shades of red, for example. The much trickier part of his work is to create a material capable of distinguishing one color from all the others. Coding for a specific shade--rather than simply determining whether the laser passes through or is reflected back--would allow much more information to be placed on a disc, increasing capacity by up to a billion times, according to Hasan.
"Aside from the excellent applications, it's beautiful physics, to study atoms inside a solid," Hasan notes. "It's not research in technology alone. It's research in the most fundamental physics. When we understand the physics, we'll understand the limitations of present materials, and be a step closer to overcoming those limitations."
In an upstairs laboratory in Temple's Barton Hall, home to the physics department, Hasan and his team prepare rare-earth materials, vaporizing them into thin, solid films that they are testing as storage materials. The experiments are carried out in a downstairs lab, where several machines shoot lasers, in brilliant greens and reds, back and forth on the materials to store and retrieve information.
Current technology permits CD surfaces to carry roughly one bit of information per square micron (one-millionth of a meter). Working under a $2 million grant from the U.S. Air Force Office of Scientific Research, Hasan is trying to expand that to 1,000--and one day, he hopes, one million--bits per micron. The result would be a staggering increase in storage capacity: A laser now reading an individual letter, for example, would instead be capable of picking up whole words.
Scientists studying this issue have identified four obstacles to making it work: permanence of the coding, high density of storage, speed of the laser's reading, and the temperature at which such memories can survive. Hasan says that his Temple group has conquered the first three, but are still trying to get the temperature right.
When they began, storage density was one-thousandth of what they have been able to achieve. The speed of storing information was less than one-millionth the present speed. And the highest temperature at which such dense memory could survive was around 2 degrees Kelvin--just above absolute zero, the point at which almost everything stops moving, except for quantum oscillations. Since then, they have managed to raise the survivability temperature to 25 degrees Kelvin, but more work is required. The issue is critical because the higher the temperature of operation, the less space and care it takes to safeguard the memory.
"We've been able to do it better than anyone so far, but it's still not good enough," Hasan explains. "It still needs to be about three times better--at least the temperature where air liquifies."
The team's short-term goal is to identify and produce materials that are more easily readable and offer compact memories. Such materials will be readily usable by the technology community. In the long run, they hope to overcome the temperature hurdle. This would "most certainly" revolutionize technology, Hasan states.
"It is the most difficult frontier to conquer; we know very little about the response of electrons in a solid to high temperature," he notes. "In scientific terms, this is known as electron-vibration coupling. But many people never thought that high-temperature super-conductivity would be possible either, and it is fairly common today. In a similar way, we are hopeful of our efforts, and are starting to make strides."
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