The Wall Street Journal-20080213-Elusive Green Laser Is Missing Ingredient For Amazing Displays

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Elusive Green Laser Is Missing Ingredient For Amazing Displays

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Imagine a projection-style TV that fits in your hand, but which can fill a whole wall with a full-color, high-resolution picture that's as bright as any you've seen. Or a light bulb an inch or two high that fills a room with pleasing white light, but without the heat and wasted energy of an incandescent bulb.

In terms of technology, we have two of the three things needed to make those happen. Already, there are efficient, inexpensive red and blue lasers. The former have been around as long as CDs, and blue lasers are now entering the home en masse inside high-resolution Blu- ray and HD DVD video players.

What's missing is a low-cost green laser to complete the red-blue- green trifecta that is the basis for most video displays and cool, "natural" room light. So important are green lasers that many physicists and material scientists talk about them in holy-grail terms. It's not quite a race to the moon, but the green-laser challenge is attracting a growing global research community, including, as of November, the U.S. government.

That's when Darpa, the famed Pentagon technology-funding agency, unveiled a green-laser initiative that included grants for nine universities and research centers, mostly in the U.S. but also in Poland.

The grant was seen as an effort to give a boost to the U.S. green- laser effort, which had been much smaller than the similar one in Japan, where the usual big consumer companies have such projects. Japan's Nichia Corp., which during the 1990s did pioneering blue laser research, is also hard at work

Darpa's usual pattern is to fund technologies that, while having potential long-term civilian applications, have a more immediate military use. The military applications for green lasers, besides projection displays in aircraft and military vehicles, are believed to include submarine-to-ship communications, because green light travels easily underwater.

Actually, green lasers sort of exist already and owe some of their popularity to the fact that you can see their beams, just like on the light sabers in "Star Wars." These devices often make the news when some goofball points one at a passing aircraft. But current green lasers are made with a process that is expensive, bulky and inefficient, at least compared with the one Darpa has in mind.

The main research effort involves finding a way to use super-low- cost, computer-style semiconductors to create green lasers, the same way red and blue lasers in consumer products are made. The semiconductors used in green lasers aren't made from familiar silicon but from other metals, notably gallium nitride and indium nitride.

Unfortunately, producing a green-laser semiconductor involves mixing more of the two metals in a single compound than the metals themselves care to have happen. "The indium just doesn't want to stay there," says Christian Wetzel, a physicist at the Rensselaer Polytechnic Institute.

That recipe difficulty is at the heart of the green-laser effort. Scientists have been working on it long enough to know that they have a tough material-science problem on their hands. Solving it means a mix of applied and theoretical science. Most of the researchers' time is spent in labs mixing stuff. They return to their desks just long enough to theorize about why their latest batch of goo did or didn't come out as planned.

Among the numerous outfits world-wide working on the problem, work is "collegial but not collaborative," said Noble Johnson, of the Palo Alto Research Center, a Darpa grant recipient. Everyone involved knows that cracking the problem will mean not only scientific plaudits, but also a steady stream of royalties from the products that will ensue.

The projection-laser displays envisioned by researchers would create wall-size images with a broader color range than displays now on the market. Fernando Ponce, an Arizona State University physicist, said a trio of red, green and blue lasers could even be used to make a futuristic, 3-D, holographic video projector.

Having a green laser costing a few dollars, and later a few pennies, would also help with the transition away from incandescent bulbs toward white-light-emitting diodes, which are increasingly being used to replace traditional bulbs. The cost of LEDs is falling, but green- laser technology could make their price plummet, said UC Santa Barbara physicist Steven DenBaars.

One product green lasers won't make possible are the higher-capacity storage products that followed blue lasers. The reason is basic optics. Compared with green ones, blue lasers have a shorter wavelength, meaning their light can be focused on a smaller area. As a result, more "blue-laser bits" can be fit onto a disk than would be possible with a green laser.

Not all green-laser engineering is taking Darpa's long-term approach. Corning, for example, has an effort using existing laser technology, said James M. Grochocinski, who manages the project. The resulting devices might not be as small, low-cost or low-power as the ones envisioned by those working in Darpa, but Mr. Grochocinski says they'll be in the market sooner. A cellphone that projects a small display could be available in a year or two, he said.

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