RICHLAND, Wash. Using lasers and tuning forks, researchers at Pacific Northwest National Laboratory have developed a chemical weapon agent sensing technique that promises to meet or exceed current and emerging defense and homeland security chemical detection requirements. The technique, called Quartz Laser Photo-Acoustic Sensing, or "QPAS," is now ready for prototyping and field testing.
PNNL, a Department of Energy national laboratory, has demonstrated QPAS's ability to detect gaseous nerve agent surrogates. In one test, researchers used diisopropyl methyl phosphonate (DIMP), which is a chemical compound that's similar to sarin. QPAS detected DIMP at the sub-part-per-billion level in less than one minute. The miniscule level is similar to letting one drop of liquid DIMP evaporate into a volume of air that would fill more than two Olympic-size swimming pools.
"QPAS is an extremely sensitive and selective chemical detection technique that can be miniaturized and yet is still practical to operate in field environments," said Michael Wojcik, a research scientist at PNNL. "The laser, tuning fork and other technology needed for QPAS are so simple, and yet robust, that further development is a low-risk investment, and we're eager to take it to the next level."
The instrument is based on Laser Photo-Acoustic Sensing, or LPAS, and infrared Quantum Cascade Lasers, or QCLs. LPAS is an exquisitely sensitive form of optical absorption spectroscopy, where a pulsed laser beam creates a brief absorption in a sample gas, which in turn creates a very small acoustic signal. A miniature quartz tuning fork acts as a "microphone" to record the resulting sound wave.
PNNL researchers paired multiple QCLs with the tuning forks, allowing simultaneous examination of a single sample at many infrared wavelengths. Nearly every molecule has unique optical properties at infrared wavelengths between three and 12 micrometers, and QCLs provide access to an
Contact: Andrea Turner
DOE/Pacific Northwest National Laboratory