For instance, infrared spectroscopy can detect even trace amounts of a wide range of chemicals, including toxic components of hazardous waste or chemical weapons, because many chemicals absorb light in the mid-infrared band.
Now Federico Capasso and his colleagues at Harvard University are developing a new type of infrared spectrometer that could be just as powerful as these bulky instruments yet fit inside a shoe box. Instead of using thermal sources for infrared rays, a team lead by Capasso, his student Benjamin G. Lee, and his postdoctoral fellow Mikhail A. Belkin, has built one of these instruments, which is powered by a tiny array of infrared quantum cascade lasers on a chip smaller than a dime. The chip holds an array of 32 lasers, each emitting a distinct wavelength and together covering a broad spectral range in the infrared region. The researchers’ new paper demonstrates that their device could identify common chemicals as well as a conventional tabletop instrument, which has a much larger footprint. It is the first time that a laser of this type, capable of such performance, has been reported.
The advantage of using a laser source is that lasers are much brighter than thermal sources thus providing a higher signal-to-noise ratio. The lasers can also be fine-tuned to provide wavelengths on demand to scan accurately for chemicals of interest—akin to having thousands of canaries, each capable of detecting a range of chemicals. (Talk CMH1, "Continuously Tunable Compact Single-Mode Quantum Cascade Laser Source for Chemical Sensing.")-Optical Society of America
