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 Advances In Optical Sensing For The 21st Century Battlefield The evolution and utility of Raman spectroscopy By Yvette Mattley S oldiers risk exposure to unseen, life-threatening hazards with each deployment. They rely on portable, field-ready instrumentation to detect hazards in the harsh battlefield setting without the luxury of a controlled, laboratory environment. It is difficult to imagine a more challenging measurement environment than the battlefield. Extreme weather conditions, unknown hazards, and the risk of imminent threats create a hostile environment for soldiers and the equipment they carry. The challenge of finding trace levels of hazardous materials in this setting is intensified by the critical size, weight, and power specifications that portable, battlefield instrumentation must meet. These compact, lightweight handheld instruments must be accurate, fast, and easy-to-operate, whether the soldier is wearing fatigues or bulky, life-saving protective gear. Field-portable devices must also provide clear, reliable, and accurate warning against unknown hazards ranging from explosives to biological warfare agents — all while minimizing false positives. After decades of technological advances and innovation in measurement techniques, optical sensing has evolved into a powerful enabling technology for the design of compact, reliable instrumentation to protect soldiers from unseen hazards on the battlefield. The continuous miniaturization of spectrometers, lasers, and other optical components at the heart of today's portable instruments has come without sacrificing the performance critical for force protection. Modern, miniature spectrometers and wavelength stabilized laser diodes pack high performance into instruments that fit into the palm of your hand. The combination of compact size and low power requirements makes these components ideal for the development of field-ready instruments that meet the size, weight, and power requirements for use on the battlefield (Figure 1). These portable systems enable the rapid detection of hazards in the battlefield setting where larger benchtop instruments cannot be used. Raman: Specificity For Confident Identification The Raman Effect was first observed in the late 1920s by C. V. Raman and K. S. Krishnan while studying light scattering in liquids using sunlight. The technique we know today showed great promise then, but it took several decades and advances in fiber optics, diode lasers, and component miniaturization before Raman became more accessible and widely used. Innovation in Raman measurement techniques followed the widespread availability of Raman instrumentation, spawning a range of new techniques based on the principle of Raman scattering. One by one these techniques overcame critical limitations of Raman spectroscopy to harness the specificity needed for the confident, reliable identification of unknown, unseen compounds in laboratories and field settings alike. Measurements with today's Raman instrumentation are so straightforward that we often take for granted how rare the Raman-scattered photon is. Raman scattering occurs following the absorption of photons by a sample illuminated with a high-powered, narrow-band laser beam. The overwhelming majority of the laser photons interacting with the sample are scattered at the same wavelength as the laser (Rayleigh scattering — elastic scattering). Only one out of a million of the laser photons is scattered at a different wavelength than the laser wavelength (Raman scattering — inelastic scattering). The inelastic scattering of laser photons from a sample yields a spectrum with peaks corresponding to the vibrational frequency of specific molecular bonds in the sample. The molecular fingerprint that results is highly specific for the chemical composition of the sample and very useful for the identification of materials. If only one in one million photons is Raman-scattered, acquiring a molecular fingerprint for trace levels of compounds in a real-world environment like the battlefield Electronic Military & Defense Annual Resource, 4th Edition 14 Figure 1: Size and portability make optical sensing ideal for field detection.