Tiny lasers enable more-sensitive chemical detection

April 23, 2008, Cambridge, MA--Federico Capasso and colleagues at Harvard University are developing a new type of infrared spectrometer that uses a tiny array of quantum cascade lasers instead of thermal sources to generate the infrared rays.

A team lead by Capasso, his student Benjamin Lee, and his postdoctoral fellow Mikhail Belkin, has built one of these instruments, which features a chip that is smaller than a dime that holds an array of 32 lasers, each emitting a distinct wavelength and together covering a broad spectral range in the infrared region.

In a paper to be presented next month at the 2008 Conference on Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference (CLEO/QELS), "Continuously Tunable Compact Single-Mode Quantum Cascade Laser Source for Chemical Sensing," the researchers demonstrate 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.