September 22, 2005

Laser may be weapon against terror

By Megan Fellman

The difficulty of detecting the presence of explosives and chemical warfare agents (CWAs) is once again all too apparent in the news about the London bombings.

In a significant breakthrough, researchers at Northwestern’s Center for Quantum Devices have demonstrated a specialized diode laser that holds promise as a weapon of defense in both civilian and military applications. Once optimized, the tiny laser could quickly detect explosives and CWAs early and warn against possible threats.

The Northwestern team, led by center director Manijeh Razeghi, became the first to create a quantum cascade laser that can operate continuously at high power and at room temperature with an emission wavelength of 9.5 microns and a light output of greater than 100 milliwatts.

Existing standard diode lasers, such as those used to read compact discs or barcodes, do not operate effectively in the longer wavelengths that are required to detect CWAs. The challenge for researchers around the world has been to develop a portable laser that operates in the far-infrared (wavelengths of 8 to 12 microns). Every chemical has a unique “fingerprint” because it absorbs light of a specific frequency, and most CWAs fall in the 8 to 12 micron region.

“Our achievement is critical to building an extremely sensitive chemical detection system,” said Razeghi, Walter P. Murphy Professor of Electrical and Computer Engineering. “One of the key elements in a successful system is the laser source. Both mid- and far-infrared diode lasers need to operate at room temperature, have high power — greater than 100 milliwatts — and be extremely small in order to keep the system portable. We have now demonstrated such a laser in the far-infrared wavelength range.”