Detecting Dangerous Substances from Their 2D Spectra

Explosives, bacteria, and chemicals can be identified from their 2D resonance-Raman spectra, even when several substances are mixed together. Identification of bacteria or chemicals with Raman spectroscopy is fast, noncontact, and does not require expendable supplies. These are all desirable characteristics for many applications. The technique uses a laser to illuminate the area that may contain the suspect substance. Some of the light is absorbed by the molecule of interest and then re-emitted at wavelengths that are slightly different from that of the laser. The spectrum of this Raman-scattered light is unique to the substance's molecular-bond structure, constituting a signature that can be used for identification. But the fraction of laser light that is Raman scattered is very small, resulting in insufficient sensitivity for many practical situations. Furthermore, the illuminated region may contain many different substances, each scattering its own Raman spectrum. The sum can be quite complex and noisy, compromising specificity and the ability to identify the constituent species. SPIE Newsroom: Optics and photonics technical articles, Apr 14, 2011. The original document contains color images.