New laser aids nanotech measurement

By United Press International   |   July 19, 2002 at 3:48 PM   |   Comments

BOULDER, Colo., July 19 (UPI) -- Researchers at a joint government-academic institute, reporting in the current issue of Science, have created laser light in the previously unattainable extreme ultraviolet spectrum, allowing detailed optical observations of processes at the molecular and atomic scale.

The team of scientists at JILA, a partnership between the University of Colorado at Boulder and the National Institute of Standards and Technology, worked around obstacles to generating coherent EUV light, which is difficult to control because of its very short wavelength.

The team's method starts with a visible-light laser with pulses as short as a femtosecond -- a quadrillionth of a second -- which excites a tiny tube of argon gas, said team co-leader Margaret Murnane, a JILA fellow and physics professor at the university. The basic process is similar to that used in green laser pointers, which use a crystal to convert an infrared laser to visible light, she told United Press International.

"We're using the (argon) atoms ... to add tens or hundreds of infrared photons to give you a much more energetic photon in the extreme ultraviolet," Murnane said.

Earlier experiments resulted in less-than-coherent light because of changes in the gas once it is excited, she said. Confining the argon at low pressure in the tube created a "waveguide" which emits truly coherent light. The system can create a laser spot only 30 nanometers in diameter, Murnane said. A nanometer is to an inch what an inch is to 400 miles.

"We've already used these EUV beams to look at molecules reacting on surfaces, to see the first steps in reactions relevant to catalysis, for example," Murnane said. "These beams tell you where an atom is and how it's bound to the surface."

Since the initial laser pulse is so short, the EUV beam can provide step-by-step views of very rapid reactions, she said. The laser's intensity is low enough to allow observations of biological processes, she said. Existing methods for probing nanoscale structures are generally used only on inorganic material.

Another advantage of the EUV laser is its relative simplicity. The system currently fits on an ordinary lab bench designed for optical work, Murnane told UPI, but should soon be reduced to the point where it would work on any researcher's desktop.

Having this sort of measurement technology be so readily available could really help nanoscience reach the mainstream of development, said Rick Snyder, chief executive officer of Ardesta, a venture-capital/technology incubation firm in Ann Arbor, Mich., that specializes in micro- and nanotechnology. The first breakthroughs in nanotech had to wait for the commercialization of tools such as the atomic-force microscope, he said.

"This (EUV tool) will make it so more people can be involved at a lower price point in terms of doing their research and tests, which helps everyone," Snyder told UPI. "The main question is ... how quickly will people grab it to do systems integration and make a device where you can simply plug it in and use it."

Some of the EUV beam's possible applications, Murnane said, include monitoring the growth of carbon nanotubes, where a single layer of atoms forms a tube only a few nanometers across. The beam could also help pharmaceutical companies determine exactly what parts of a drug molecule interact with cells, she said.

The system's basic laser components could be assembled for about $5,000, the JILA team said. That might be a bit optimistic, Snyder said, although developers have already done work on systems integrating with femtosecond lasers.

Other recent nanoscale measurement research in Germany also achieved 30-nanometer resolution, but used fluorescent light, which has fewer nanotech applications. That procedure also requires an additional laser. The first causes a dye to fluoresce, the other stops the emitted light except in a nanometer-scale gap in the second laser's interference pattern.

(Reported by Scott Burnell, UPI Science Correspondent, in Washington)

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