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Red laser light gets an electric charge.

Lasers - devices that produce intense monochromatic beams of electromagnetic radiation - are rapidly lighting the way to advances in communications technologies. Now, laser-based systems for storing, presenting, and moving data may benefit from a new semiconductor laser with potential uses in optical information processing, laser printers and displays, and scanners that read bar codes at supermarket checkouts, two materials scientists report in the May 13 ELECTRONICS LETTERS.

Richard P. Schneider Jr. and James A. Lott, both at Sandia National Laboratories in Albuquerque, N.M., have created a vertical-cavity surface-emitting laser (VCSEL) that should bring this promising class of devices closer to commercialization. Most semiconductor lasers used today emit their light from the cleaved edges of a crystal. The much smaller VCSELs, however, emit a more focused swath of light from the top surface. Scientists can closely pack an array of these devices on a chip to produce tight, circular laser beams (SN: 7/29/89, p.68).

The Sandia team has now developed a VCSEL that emits visible light and operates using electricity -- two significant advances, says Schneider. Until now, the shortest wavelength reported for a VCSEL was 699 nanometers, just at the edge of the visible-light spectrum. The new VCSEL lases bright red light at wavelengths of 639 to 661 nanometers. Scientists are interested in shorter wavelengths because they're visible to the human eye and can carry and detect smaller informational features, says Schneider.

To make their VCSEL, he and Lott used metalorganic vapor phase epitaxy, a technique for stacking perfect crystalline layers into a semiconductor "sandwich." Thin layers of metallic phosphides containing indium, aluminum, and gallium make up the optically active region, which determines the wavelength of the resulting beam. Alternating layers of aluminum arsenide act as reflectors, sending light waves out the top surface of the material.

Even more important, Schneider says, he and Lott managed to stimulate light emission through electrical injection. Before that, they depended upon another laser to charge their VCSEL -- hardly practical in everyday applications. "You want to be able to plug something into the wall," says Schneider. "We knew we wouldn't have a 'real' device until it operated with electrical injection. That's the breakthrough here."

The team is now trying to boost the device's electrical efficiency and coax it to produce other colors of light.
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Title Annotation:new semiconductor laser could be used in optical information processing
Author:Schmidt, Karen F.
Publication:Science News
Article Type:Brief Article
Date:May 22, 1993
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