Raman spectroscopy is an analytical technique with vast applications in the homeland security and defense arenas. The Raman effect is defined by the inelastic interaction of the incident laser with the analyte molecule’s vibrational modes, which can be exploited to detect and identify chemicals in various environments and for the detection of hazards in the field, at checkpoints, or in a forensic laboratory with no contact with the substance. A major source of error that overwhelms the Raman signal is fluorescence caused by the background and the sample matrix. Novel methods are being developed to enhance the Raman signal’s sensitivity and to reduce the effects of fluorescence by altering how the hazard material interacts with its environment and the incident laser. Basic Raman techniques applicable to homeland security applications include conventional (off-resonance) Raman spectroscopy, surface-enhanced Raman spectroscopy (SERS), resonance Raman spectroscopy, and spatially or temporally offset Raman spectroscopy (SORS and TORS). Additional emerging Raman techniques, including remote Raman detection, Raman imaging, and Heterodyne imaging, are being developed to further enhance the Raman signal, mitigate fluorescence effects, and monitor hazards at a distance for use in homeland security and defense applications. 1. Introduction There are a number of factors driving research, development, and acquisition of new technologies for detecting chemical, biological, radiological, nuclear, and explosive (CBRNE) threat materials. The addition of new and emerging threats has increased in recent years and, with these new agents, the number and type of physical properties to be detected have also increased. Historically, the Department of Defense prepared to defend against the mass use of war gases, such as chlorine or phosgene, or less volatile nerve and blister agents (Sarin, sulfur mustard, etc.), which could still present a substantial vapor hazard under certain environmental conditions. More recently, low volatility nerve agents, such as VX, or aerosol-based biological agents, such as Bacillus anthracis (anthrax), became the prevalent threats and increased the need for robust aerosol and point detection capabilities to detect these agents. As the potential for Cold War-style engagements of massed armies with large quantities of weaponized chemical and biological agents receded, the need has increased to defend against and deter small-scale attacks of increasingly toxic emerging chemical and biological (CB) agents from rogue states, nonstate parties, or
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