ABSTRACT
This chapter considers the challenge of using terahertz (THz) techniques for the detection and recognition of explosives. There are two general approaches to this problem: (1) imaging, which uses the penetration capability of THz radiation to
12.1 Introduction .................................................................................................. 323 12.1.1 Background ....................................................................................... 324 12.1.2 Nomenclature and Communities ...................................................... 324 12.1.3 Bandwidths, Technology, Phenomena, and Names .......................... 325 12.1.4 History .............................................................................................. 325
12.2 The Physics ................................................................................................... 326 12.2.1 Blackbody Radiation and Noise ....................................................... 326 12.2.2 Townes Noise .................................................................................... 328 12.2.3 Interactions with Matter ................................................................... 329
12.2.3.1 Interactions with Gases ...................................................... 330 12.2.3.2 Atmospheric Propagation................................................... 332 12.2.3.3 Interactions with Solids and Liquids ................................. 333
12.3 Applications .................................................................................................. 334 12.3.1 Gas-Phase Point Sensing .................................................................. 334 12.3.2 Gas-Phase Remote Sensing .............................................................. 339 12.3.3 Detection of Solid Explosives ........................................................... 341
12.4 Cheap and Practical ...................................................................................... 342 12.5 Summary ...................................................................................................... 343 12.6 Acknowledgments ......................................................................................... 343 References .............................................................................................................. 343
“see” the image of the explosive, and (2) spectroscopy, which allows the chemical signature to be recognized. The former is beyond the scope of this volume and has been well addressed previously.1 The latter can be divided into two subcategories: the detection and recognition of the explosive itself and the detection and recognition of its precursors, additives, or decay products. Most reports claiming detection of these materials, hereafter collectively called “explosives,” have only considered laboratory measurements of them in pure form and have not considered the greater challenge of recognizing these materials among naturally occurring compounds or mixed with other compounds and shielded in containers. When these challenges are considered seriously, the exquisite recognition specicity afforded by gas-phase THz spectroscopy may only be used to detect and recognize explosives in very limited circumstances.
