Shining a Light on Breakthroughs in Laser Technology
Scientists around the world are closing in on a new technology that will affect everything from the lights in your living room to electronic warfare.
The heart of the technology consists of light-emitting diodes, commonly abbreviated as LEDs, a solid-state system the size of a silicon wafer that produces light of various wavelengths. The stakes are so high that, despite enormous technological hurdles that must be overcome, this technology is sure to emerge soon as a dominant player in the rapidly growing field of optic-electronics.
“We’re right at the threshold of some really great breakthroughs, some really major improvements in electronics,†said Colin Wood, an electronics engineer at the Office of Naval Research, which is funding some of the work.
Much of the excitement in the research community centers on blue light lasers, which promise to vastly increase the storage capacity of everything from hard disk drives to video players.
“In the future, how much you can record on a single disk is determined completely by how tightly you can focus the light,†said Umesh K. Mishra, professor of electrical and computer engineering at UC Santa Barbara, one of the leading research centers in the field.
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For example, compact disc players use an infrared laser to read data from the disc. The move to a shorter wavelength, red, made the age of digital video disks possible.
Now the goal is to take that to the next step, blue lasers, which are able to focus on a much smaller area and thus cram more data into the same space. It’s a little like a farmer loading boxes with oranges and cherries. He can get in a lot more cherries because they pack together closer than oranges.
Merely switching from infrared to red enabled the industry to move from 800 megabytes on a compact disc to 17 gigabytes on a DVD, according to Robert Trew, director of research for the Defense Department.
“If you could take that same technology but use blue lasers, you would increase your capacity by at least a factor of three, so you are talking in the realm of about 50 gigabytes on a single disk,†Trew said.
Through research funded by the Defense Advanced Research Projects Agency, UCSB developed diodes that emit blue light, and the university has joined with the semiconductor materials giant Emcore to develop diodes that are expected to replace conventional lighting. (Emcore and GE Lighting recently formed a new company, GELcore, to design and market the new solid-state lighting products.)
According to a company statement, the new lights are expected to be very energy-efficient and have a life span of 100,000 hours.
“An LED basically is an energy converter,†UCSB’s Mishra said. “It converts electricity into light.†The color of the light depends on the material used in the diode. Gallium nitride, for example, produces blue light.
Blue light can be converted easily to white light by simply coating the device with phosphorous.
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However, it is a quantum leap from a device that will work for household lighting to a laser that will emit pure light of a specific wavelength, and that is where most of the research is concentrated today. Only one researcher, Shuji Nakamura of Nichia Chemical Industries Ltd. in Japan, has succeeded in making a blue light laser that operates continuously.
“Nakamura has a two-year lead over anybody else in the world in blue lasers,†said ONR’s Wood.
Nakamura tantalized other researchers recently during a technical conference in Juneau, Alaska. About 50 experts from around the world took part in the conference, and each used a traditional red laser as a pointer while displaying charts of their work.
But when Nakamura got up to speak, he used a small, hand-held blue laser pointer.
“I would like to know how he does that,†said Mishra, whose university has produced the only blue light laser diode in this country. However, it operates only as a pulse laser, not a continuous beam, thus limiting its applications.
The technology is so challenging because of the materials that must be used.
The diodes are formed by subjecting the materials to extremely high temperatures and pressures. The gallium nitride is sandwiched between a harder substrate, usually either sapphire or silicon carbide, and the temperature is revved up to about 1100 degrees Celsius.
Mishra compares it to making a sandwich.
“It’s like slapping two layers of bread with peanut butter in the middle†and keeping the peanut butter from oozing out when the sandwich is placed in the oven, he said.
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The problem is that as the gallium nitride grows, it develops flaws called dislocations, which are like holes or tears in the material. Those holes can emit light of the wrong wavelength, diminishing the quality of the laser.
Several techniques to eliminate that are being explored.
Even blue light lasers are just one step on the way to this revolution, however. The next step is green lasers.
“When you have red, blue and green lasers, you have the three primary colors,†Mishra said. “If you have these three, then you can make large-scale projection television systems of cinematic quality.â€
The Defense Department isn’t really all that interested in sharper movies. But the same technology has many other applications, including high-definition microwave radar.
Blue-green lasers are of special interest to the Navy, because light of that color propagates so well through water, paving the way to better detection systems for enemy submarines.
“We will be big users of the technology,†said ONR’s Wood.
So the military, with its own objectives, is teamed with universities and industry to create devices that almost surely will affect us all in many ways.
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Lee Dye can be reached at [email protected].
