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Mobile Raman Targets Chemical Spills

Photonics Spectra
Feb 2001
Kevin Robinson

A few years from now, emergency personnel responding to a chemical spill at a train wreck may be able to breathe a little easier.

Scientists at Brookhaven National Laboratory are testing a portable Raman spectroscopy system that will enable open-air measurements of environmental contaminants from more than 1700 feet away.

Researchers at Brookhaven National Laboratory have developed a mobile Raman spectroscopy system to remotely assess unknown chemical spills in emergency situations. The system uses 266-nm Raman lidar to target samples more than 1700 feet away.

The Mobile Raman Lidar Van arose from research into Raman spectroscopy for lidar, explained Arthur J. Sedlacek III, optical remote sensing and spectroscopy group leader in the laboratory's environmental sciences department. "We slowly became aware of the need of the first-responder community to be able to identify unknown chemical spills prior to handling," he said. Currently, Hazmat personnel must bring a sensor close to a spill or collect a sample for testing.

"The Mobile Raman Lidar Van is designed to interrogate puddles or perhaps residues on a surface," Sedlacek said. Cleanup scenarios include train derailments, chemical manufacturing accidents and transport truck accidents.

Essentially Raman lidar in a step-van delivery truck, the system employs an Nd:YAG laser operating at 266 nm, mounted on an optical table. The laser beam is expanded 3.5 times before it leaves the van, so the spot is roughly 150 mm wide when it reaches the sample. A 16-inch Cassegrain receiver telescope collects the Raman signal, which is filtered and focused on the entrance of a single-grating spectrometer. An intensified CCD camera records the spectra.

By using a 266-nm laser, the researchers virtually eliminate signal contamination from other sources of light sources. The wave length is in a solar-blind region of the spectrum, thanks to the ozone layer, which blocks UV light below 300 nm, and few man-made light sources emit in this region. Therefore, the researchers did not need to reduce background illumination.

The system is not without risks, however. "Since we are operating a Class IV laser system, it is inherent-ly noneye-safe," Sedlacek said. "Therefore, we have had to take the obvious safety precautions prior to sample interrogation."

In proof-of-principle tests reported in Applied Spectroscopy, Vol. 54, No. 6, the group identified Teflon, cyclohexane and acetonitrile at distances greater than 1700 feet. Brookhaven is negotiating a collaborative agreement with ITT Industries Inc. of White Plains, N.Y., to develop a smaller version, called the Mini-Raman Lidar System. This system will be more portable and will have a shorter working distance for identifying domestic chemical spills, or investigating suspected terrorist activity or industry compliance with environmental standards.

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