A new approach to chemical detection

Published 21 March 2007

Researchers at the Pacific Northwest National Laboratory use lasers and quartz crystals to create a portable and rugged chemical weapons detection system

This is new. Researchers at Pacific Northwest National Laboratory have developed a chemical weapon agent sensing technique that relies on lasers and tuning forks. Called Quartz Laser Photo-Acoustic Sensing (QPAS), the approach uses Laser Photo-Acoustic Sensing (LPAS) — a form of optical absorption spectroscopy in which a pulsed laser beam creates a brief absorption in a sample gas, which in turn creates a very small acoustic signal that can be detected by a quartz tuning fork. “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 researcher Michael Wojcik. “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.”

Tests performed on the QPAS system provide hope that Wojcik and his colleagues will succeed in that effort, although so far they have focussed only on chemical weapon surrogates. Key to the system’s success, it seems, will be its small size. LPAS instruments are typically quite large and prone to interference from outside noises and vibrations — not good if one intends to deploy them to a battle zone or disaster area. In the QPAS technique, however, several Quantum Cascade Lasers (QCLs) can fit on a 3 x 3 millimeter chip, and the tuning forks used are the same kind used in wristwatches. According to the researchers, the QPAS’s conceptual design fits into a briefcase and would weigh less than 15 pounds. “Because of this access and the fact that QPAS is almost immune to acoustic interference, we have potential for extraordinary chemical sensitivity and selectivity,” Wojcik said.