Holography A Picture is Worth 100,000 Bits By Gary GoettHng Photography by Gary Meek
T
he picture of the clown's head seems so lifelike, it's unsettling. As you move past the portrait, he blows a noisemaker that unfurls out into the air. Perhaps it's the picture's greenish cast that gives it a corpse-like eerieness reminiscent of a character in a Stephen King novel. It's easy to become absorbed in the details of the image, and you have to pinch yourself: This is only a hologram. From the Greek holos, meaning whole, and graphos, meaning to write, holography is old technology that is finding new life in areas including security, quality control, marketing, information storage— even fine arts, as in the example of the clown. At Georgia Tech, researchers are using holographic processes to make computers faster, and capable of storing extraordinary amounts of data. Their studies could help bring movies on demand into homes via fiber-optic networks, hasten integration of computing and video technologies, or bring resources of the Library of Congress into classrooms. A hologram is essentially a recording of an object taken with laser light. The theoretical framework of holography—that a coherent light source could record images in three dimensions—was developed in 1947 by Dr. Dennis Gabor, who was searching for a way to improve the s quality of photographs from electron 16
GEORGIA TECH • Fall 1992
microscopes. His discovery won for him the 1971 Nobel Prize in physics. But not until the invention of the laser in I960 did holography become practical. Holography is possible because of the peculiar nature of laser light. Sunlight is a mishmash of wavelengths of all colors, each wave traveling independently of the others. A laser beam, on the other hand, is coherent, meaning that it possesses a high degree of organization and contains a single wavelength of the spectrum. Early lasers emitted red light because the crystalline structure of rubies was the most amenable to energizing. Since then, scientists have been able to lase almost any substance: other crystals, gasses, liquids—even Jell-O and human breath.
Dime-Size Novels
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or more than three decades, scientists have dreamed of exploiting holography as a means of storing and retrieving information. The 30-year holdup has been in finding the "right" medium. But with increasing pressure to make computers faster, smaller and more efficient, the search has been renewed. The potential is staggering: With the right storage medium, data equivalent to a thousand books could be holographically placed on something the size of a dime. The awesome capacity of holographic
storage is also evident in how the data is measured. Computer infonnation is expressed in bits, whereas holographic data is termed pages, with each page containing 100,000 bits or more. "A lot of research and development is oriented toward the storage material itself," says electrical engineering Professor Thomas K. Gaylord. "There's no perfect material at the moment. Various materials have advantages and disadvantages. There are tradeoffs involved witli sensitivity, storage lifetime and the ultimate maximum data capacity." Gaylord, along with HE Professor Elias Glytsis, is placing holograms inside crystals of lithium niobate in an effort to understand how one hologram affects another, and how stable the information remains over time.
Crystal Pages
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he holographic storage process works like this: A laser light is split in two, and one of the rays (reference beam) is I x >unced off a mirror so that it hits the opti-sensitive storage crystal such as lithium niobate at a certain angle. The other beam (object beam) passes through a device containing a page of data, which is presented as thousands of Continued
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The hologram of a clown at the Elusive Image gallery in Atlanta contains multiple images, so the clown appears to move as the viewer walks past it