The Northwestern team, led by centre director Manijeh Razeghi, became the first to create a quantum cascade laser (QCL) 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.”
This research is part of a four-year program called Laser Photoacoustic Spectroscopy (LPAS) funded by the Defense Advanced Research Projects Agency (DARPA). The goal of the program is to develop a man-portable system that can warn against a large number of potential threats using mid- and far-infrared diode lasers. Once optimised, such lasers would be a very reliable means of detecting explosives and chemical warfare agents while distinguishing them from benign chemicals present in the atmosphere.
During the next two years Razeghi and her team will work to put together a detection system based on the centre’s far-infrared laser. The system will then be evaluated by DARPA for use by the military.