%0 Journal Article
%T Demonstrated Wavelength Portability of Raman Reference Data for Explosives and Chemical Detection
%A Timothy J. Johnson
%A Yin-Fong Su
%A Kristin H. Jarman
%A Brenda M. Kunkel
%A Jerome C. Birnbaum
%A Alan G. Joly
%A Eric G. Stephan
%A Russell G. Tonkyn
%A Robert G. Ewing
%A Glen C. Dunham
%J International Journal of Spectroscopy
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/297056
%X As Raman spectroscopy continues to evolve, questions arise as to the portability of Raman data: dispersive versus Fourier transform, wavelength calibration, intensity calibration, and in particular the frequency of the excitation laser. While concerns about fluorescence arise in the visible or ultraviolet, most modern (portable) systems use near-infrared excitation lasers, and many of these are relatively close in wavelength. We have investigated the possibility of porting reference data sets from one NIR wavelength system to another: We have constructed a reference library consisting of 145 spectra, including 20 explosives, as well as sundry other compounds and materials using a 1064£¿nm spectrometer. These data were used as a reference library to evaluate the same 145 compounds whose experimental spectra were recorded using a second 785£¿nm spectrometer. In 128 cases of 145 (or 88.3% including 20/20 for the explosives), the compounds were correctly identified with a mean ¡°hit score¡± of 954 of 1000. Adding in criteria for when to declare a correct match versus when to declare uncertainty, the approach was able to correctly categorize 134 out of 145 spectra, giving a 92.4% accuracy. For the few that were incorrectly identified, either the matched spectra were spectroscopically similar to the target or the 785£¿nm signal was degraded due to fluorescence. The results indicate that imported data recorded at a different NIR wavelength can be successfully used as reference libraries, but key issues must be addressed: the reference data must be of equal or higher resolution than the resolution of the current sensor, the systems require rigorous wavelength calibration, and wavelength-dependent intensity response should be accounted for in the different systems. 1. Introduction There are many spectroscopic methods that have decreased the size and cost of the instruments and simultaneously increased their detection potential so as to become routine methods for chemical detection: infrared spectroscopy [1¨C3], visible-NIR reflectance [4], terahertz methods [5, 6], and others. Recently Raman spectroscopy has followed this trend and evolved from a cumbersome method of chemical physics to a common forensic technique [7]. There are currently tens of thousands of deployed spectrometers, many on-line or at-line, and in recent years there has been an advent of portable, even handheld, systems [8, 9], as well as remote sensing devices [10, 11]. Such capabilities make Raman an especially attractive method in the security arena, where substances such as radioactive materials,
%U http://www.hindawi.com/journals/ijs/2012/297056/