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NMSU researchers demonstrate major advance in laser technology

NMSU physicists have achieved dramatic results in experiments with a new composite material that enables lasers to operate at extremely low power levels. Shown here in their laboratory, left to right, are NMSU physics professor Robert Armstrong and Vladimir Shalaev, visiting Russian scientist Vladimir Safonov, and NMSU graduate student Won-Tae Kim.

(NMSU photo by Michael Kiernan)

New Mexico State University physicists have developed a new class of composite material that enables lasers to work at extremely low power levels, opening the door to cheaper and smaller lasers with an array of new uses.

Robert L. Armstrong and Vladimir M. Shalaev, NMSU physics professors, have achieved dramatic results in experiments combining two types of materials -- fractal materials and microcavities -- to enhance a laser's efficiency.

Since the first lasers were built just 40 years ago, advancements in the technology have led to laser surgery, compact disks, bar-code scanners, fiber-optic communications and other applications. The work of Armstrong and Shalaev, assisted by NMSU graduate students and visiting scientists, promises a new generation of lasers -- tiny, low-power, highly efficient lasers that could improve on existing uses and create entirely new ones.

An article on their findings has been accepted for publication this summer in Physical Review Letters, a leading journal of physics. Co-authors with Armstrong and Shalaev are NMSU graduate student Won-Tae Kim and Vladimir P. Safonov of the Institute of Automation and Electrometry, Siberian Branch of the Russian Academy of Science.

The research is a natural collaboration for Armstrong, an authority on the effects of microcavities in optical physics, and Shalaev, whose expertise is in fractal materials.

Microcavities are extremely small optical devices, often no thicker than a human hair, that can emit intense laser light. A fractal has a geometric shape that is "self-similar," Shalaev said. "That means its structural patterns are repeated on a progressively smaller scale." A small piece of a fractal, when magnified, has roughly the same geometric pattern as the whole, as does a piece of that piece, and so on.

Both types of materials have been shown to increase the efficiency of lasers, so the researchers saw potential for combining the two. They created a composite that consists of a fractal material inside a microcavity.

When the scientists conducted experiments using the new composite, they were surprised to find that the advantages of the two materials were not simply added -- the effects were multiplied.

"It was not A plus B, it was A times B," Shalaev said.

"I wasn't prepared for results of this magnitude," added Armstrong.

The composite proved to be about 100 million to 100 billion times more efficient than materials typically used in lasers. The dramatic enhancement means lasers can be created with much less power, using micro-size components.

A laser -- the word originally was an acronym for Light Amplification by Stimulated Emission of Radiation -- creates a narrow, intense beam of coherent light. A typical laser today consists of two parts, Armstrong said: a pumping source, which may itself be a laser, and the output laser. In the pump, an electrical current is applied to a substance, often a mix of helium and neon gas, to create a beam that is aimed at the output laser. In the output laser, which is a cavity or resonator containing another substance that interacts with the light, molecules are further "excited" until a narrow, coherent beam is emitted.

"It's typically necessary to have a relatively powerful pump, and the pumping source is the big expense in making a laser," Armstrong said. An output laser utilizing the new composite material requires much lower pump energies. Out of curiosity, the researchers tried using an inexpensive laser pointer as the power source in one experiment. It worked.

For their experiments, the researchers' students fabricated cylindrical microcavities made of quartz with a fractal material made of silver inside.

"We have been probing this at a fairly coarse scale," Armstrong said. Now that the dramatic results have been confirmed, he said, "we will repeat it at a very small scale."

Armstrong and Shalaev foresee a wide range of applications for lasers using their new composites, including advances in optical computers, which Armstrong said are 1,000 to 10,000 times faster than existing computers.

The research also could have important applications in spectroscopy, allowing analysis of single molecules. Because molecules can be chemically identical yet structurally different, "single molecule detection is a very exciting new field," Armstrong said.

Karl Hill
April 26, 1999