8 October 2007 Raman spectroscopy of illicit substances
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Raman spectroscopy provides a very effective method of identifying an illicit substance in situ without separation or contact other than with a laser beam. The equipment required is steadily improving and is now reliable and simple to operate. Costs are also coming down and hand held portable spectrometers are proving very effective. The main limitations on the use of the technique are that it is insensitive in terms of the number of incident photons converted into Raman scattered photons and fluorescence produced in the sample by the incident radiation interferes. Newer methods, still largely in the development phase, will increase the potential for selected applications. The use of picosecond pulsed lasers can discriminate between fluorescence and Raman scattering and this has been used in the laboratory to examine street samples of illicit drugs. Surface-enhanced Raman scattering, in which the analyte requires to be adsorbed onto a roughened metal surface, creates a sensitivity to compete with fluorescence and quenches fluorescence for molecules on a surface. This provides the ability to detect trace amounts of substances in some cases. The improving optics, detection capability and the reliability of the new methods indicate that the potential for the use of Raman spectroscopy for security purposes will increase with time.
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Robert J. Stokes, Robert J. Stokes, Karen Faulds, Karen Faulds, W. Ewen Smith, W. Ewen Smith, } "Raman spectroscopy of illicit substances", Proc. SPIE 6741, Optics and Photonics for Counterterrorism and Crime Fighting III, 67410Q (8 October 2007); doi: 10.1117/12.739081; https://doi.org/10.1117/12.739081

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