SAN FRANCISCO--Scientists have created a new type of ultraviolet laser that might be modified to read compact discs. If so, then the invention, reported here yesterday at a meeting of the Materials Research Society, could lead to CDs and CD-ROMs packed with far more information than they come with today.
Current CD lasers use gallium arsenide chips that emit near-infrared light. Over the last few years, however, researchers worldwide have been racing to commercialize blue lasers, which have a shorter wavelength than near-infrared light. Because a laser reads indentations in a CD burned by one of a matching wavelength, using lasers with a shorter wavelength would decrease the size of the indentations--thus increasing the data. Blue-laser CDs could store four times as much information as current versions. But ceramics researcher Masashi Kawasaki and his colleagues at the Tokyo Institute of Technology may have found a way to beat the blues: with ultraviolet light, which has an even shorter wavelength than blue light.
His team made thin, centimeter-sized ceramic films from a common material composed of zinc oxide. Large ZnO crystals emit diffuse ultraviolet light, with a range of wavelengths, when hit with UV photons from a large UV laser. To get these crystals to function as lasers and emit coherent UV light, scientists would have to surround them with precise mirrors that reflect and amplify photons produced at a single wavelength--a task that most researchers had written off as too unwieldy a long time ago.
Kawasaki, however, found a clever way to circumvent this problem. His group grew a film of ZnO crystals forming a honeycomb of tiny hexagonal crystallites. The boundaries between crystallites illuminated by a laser and those not in the light's path act as tiny mirrors to reflect UV photons and funnel them into a coherent beam. The technique is "a real breakthrough," says materials scientist Darrell Schlom of Pennsylvania State University in University Park.
For now, however, the new films produce laser light only when blasted by UV photons from another laser--a situation that makes them too cumbersome for use in consumer electronics products like CD players. The next step, Kawasaki says, is to develop compact ZnO chip-based lasers that generate photons after having electricity passed through them. Such lasers will have an instant leg up on the market: Unlike the most popular material for blue lasers--gallium nitride--ZnO films could be grown at far lower temperatures and likely could be fabricated more easily.