The atoms in a molecule can bend, stretch and rotate with respect to one another, and these excitations are largely optically active. Most molecules, from simple to moderately complex, have a characteristic absorption spectrum in the 3- to 14-µm wavelength range that can be uniquely identified and quantified in real time. Infrared spectroscopy has been used to study these absorption features and develop different molecular “fingerprints.” The benefits of this optical technique, as opposed to chemical sensors or chromatography, are that the detection mechanism requires minimal sample pretreatment and is very fast. While high-performance infrared detectors have existed for a long time, the main challenge in achieving the full potential of tunable laser spectroscopy lies in the performance limitation of the tunable mid-infrared (IR) laser sources.
Read more at: http://www.photonics.com/Article.aspx?AID=61166