Electronic Military & Defense magazine was developed for engineers, program managers, project managers, and those involved in the design and development of electronic and electro-optic systems for military, defense, and aerospace applications.
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Technology Electronic Military & Defense Annual Resource, 4th Edition 15 represents a significant challenge. The challenge increases when background fluorescence occurs following exposure to the high-powered laser used to induce Raman scattering. This fluorescence can overwhelm the weak Raman signals, making them difficult or even impossible to detect. Innovative researchers who saw the value of Raman did not allow the rarity of the Raman-scattering phenomenon to limit the Raman technique. They developed a number of related techniques to overcome these limitations and to help establish Raman as the powerful optical sensing technique it is today. These related techniques overcome several of the limitations associated with Raman including sensitivity, interference from sample containers, and background fluorescence. Sensitivity is one of the biggest limitations of Raman spectroscopy. The inefficiency of Raman scattering once limited Raman instrumentation such that high-powered lasers and ultrasensitive detectors were required for trace detection. In the 1970s, work with silver substrates by Fleischmann and Van Duyne introduced us to surface-enhanced Raman spectroscopy (SERS) with the potential to enhance the intensity of Raman scattering by more than one million times when the samples were measured in the presence of roughened metal substrates. The signal enhancement is so high that, in some cases, SERS has enabled the collection of Raman spectra from just a single molecule. The increase in sensitivity achieved with SERS enables the highly specific detection of trace materials including explosives and biological warfare agents. For field use, SERS substrates can be developed into a range of form factors including swabs that enable the rapid sampling of trace materials from a surface in a battlefield setting. Raster orbital scanning (ROS) — more on this later — improves sensitivity further by overcoming the variation in nanoparticle density that often limits SERS measurements (see Figure 2 on the next page). The ability to make measurements through the wall of a container to avoid exposure to potentially hazardous materials is a major advantage of Raman spectroscopy. While glass sampling vials and vessels used in the laboratory setting (YDQVFDSVDUHDOZD\VVSHFLÀHGLQKXQGUHGVRIGHIHQVHFULWLFDODLUPLVVLRQVEHFDXVH WKH\DUHDOZD\VPRUHHQHUJ\GHQVHDOZD\VUHDG\DQGDOZD\VUHOLDEOH (YDQVFDSVKDYHPRUHLQWKHLUKHUPHWLFWDQWDOXPSDFNDJHVWKDQDQ\RWKHUFDSDFLWRU 7KH\ZHUHGHOLYHUHGWRRYHUDHURVSDFHDQGGHIHQVHFXVWRPHUVODVW\HDU (YDQVFDSVWKHFDSDFLWRUVRIFKRLFHIRUSKDVHGDUUD\UDGDUODVHUWDUJHWLQJDYLRQLFV GLVSOD\VFRPPXQLFDWLRQVZHDSRQVV\VWHPV-756VRIWZDUHGHÀQHGUDGLRVSDFH V\VWHPVDQGSRZHUKROGXS$OZD\V 10V to 125V Low ESR >100 Amp Discharge Unlimited Cycle Life High Shock and Vibe 5 Million Hour MTBF - 55°C to 125°C Operation w w w. e v a n s c a p . c o m for specs and pricing Since 1996 EVANSCAPS ALWAYS The Evans Capacitor Co. %R\G$YHQXH (DVW3URYLGHQFH5,86$ )$;FKDVG#HYDQVFDSFRP