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Laser Technology Could Instantly Identify Environment Hazards

Photonics.com
Oct 2002
WASHINGTON, Oct. 2 -- New research indicates that a novel laser technique may provide tremendous assistance in strengthening homeland security. Laser-induced breakdown spectroscopy (LIBS) has the power to instantly detect and identify a wide variety of target materials, including chemical substances in the environment as well as explosives and biological agents, according to researchers.

"The implications of this technology are astounding," said Andrzej Miziolek (pronounced miz-E-oh-lek), a scientist at the US Army Research Laboratory and program chair of LIBS 2002, a meeting devoted to this laser technique. He was among the researchers from around the world who discussed this technique at a meeting last week sponsored by the Optical Society of America (OSA).

"Since Sept. 11, there has been a heightened need for better sensors and methods to detect explosives, biological and chemical agents. LIBS technology has the potential to allow us to do this very thing with an unprecedented level of versatility and robustness."

By emitting a powerful laser pulse that heats a tiny spot of matter to temperatures greater than some parts of the sun, LIBS breaks down the target unknown substance to its atomic constituents. Heated and raised to a high-energy state, the unknown sample radiates its "elemental fingerprints," a unique spectrum of light that provides a valid, indisputable identification of the substance. Preliminary work with this technology has shown that not only can it detect explosives, but it can also identify and differentiate between several close relatives of anthrax. Recent breakthroughs in instrumentation highlight LIBS' potential to detect and identify any known substance.

Researchers have conceptualized a LIBS wand to examine suspicious materials. The versatility of LIBS could allow workers to fire the laser to analyze a target that is hundreds of feet away, or designers can thread it through fiber optics to analyze concealed materials -- a capability that would be helpful for monitoring many locations with difficult access.

In recent laboratory work, researchers have shown the ability to detect different explosives using a single shot. LIBS' effectiveness has also been demonstrated on three strains of bacteria, all closely related to the bacterium that causes anthrax. Analysis of the LIBS spectra indicated at least 15 differences between the three bacilli spores, BC, BG, and BT.

While more research and testing must be conducted to make the use of this technique a widespread reality, these practicalities have not stopped LIBS researchers from envisioning the possibilities for improving homeland security. For example, they believe that at subway stations and other high traffic environments, a LIBS system could monitor the air for signs of chemical or biological agents on a continuous basis, alerting officials if a possibly hazardous substance is present in the surrounding environment. This would provide officials the time to react and evacuate the area before the substance causes any harm.

A LIBS laser pulse heats a tiny portion of the target sample to temperatures of up to 43,000 degrees Fahrenheit (approx 24,000 degrees Kelvin), hotter than some parts of the sun. The laser pulse-lasting just nanoseconds, or billionths of a second-zaps a specimen, such as an unknown powder, a test tube containing suspicious bacteria, or even a spot of air.

The extreme heat breaks matter into plasma -- a collection of neutral atoms and ions (positively charged atoms and molecules) and negatively charged electrons. After about a millionth of a second, the ions and electrons combine to form atoms and molecules again. But now these atoms and molecules are highly energized-with a significant amount of extra energy to lose. To shed this energy, each kind of atom or molecule radiates different colors of light, and since scientists recognize what colors of light an atom will emit in every element, this gives away the identity of the substance.

LIBS has the potential to identify any known substance, from what is in a volcanic rock to a particular strain of bacteria to an unknown explosive. Once LIBS detects the types and quantities of chemicals, it consults chemical profiles of known substances, like TNT. If the instrument records a certain proportion of carbon, nitrogen, hydrogen and oxygen, it can then check a computer database to see if this matches the exact proportion of elements in TNT, or any other substance in the database.

The OSA meeting topics included an analysis of using LIBS for studying Mars, using LIBS in archeology, detecting kidney stones and analyzing gunshot residue for forensics studies. New commercial laboratory LIBS systems and advanced components, as well as field portable systems, was also discussed.

For more information, visit: www.osa.org



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