Standoff detection of explosive substances at distances of up to 150 m

Abstract

We report detection and identification of trace quantities of explosives at standoff distances up to 150 m with high sensitivity (signal-to-noise ratio of approximately 70) and high selectivity. The technique involves illuminating the target object with laser radiation at a wavelength that is strongly absorbed by the target. The resulting temperature rise is observed by remotely monitoring the increased blackbody radiation from the sample. An unambiguous determination of the target, TNT, in soil samples collected from an explosives test site in China Lake Naval Air Weapons Station is achieved through the use of a tunable CO(2) laser that scans over the absorption fingerprint of the target explosives. The theoretical analysis supports the observation and indicates that, with optimized detectors and data processing algorithms, the measurement capability can be improved significantly, permitting rapid standoff detection of explosives at distances approaching 1 km. The detection sensitivity varies as R(-2) and, thus, with the availability of high power, room-temperature, tunable mid-wave infrared and long-wave infrared quantum cascade lasers, this technology may play an important role in screening personnel and their belongings at short distances, such as in airports, for detecting and identifying explosives material residue on persons.

Thulium pumped mid-infrared 09–9μm supercontinuum generation in concatenated fluoride and chalcogenide glass fibers

“…Absorption bands of atmospheric molecules, such as CO 2 and NO x , likewise reside within this part of the spectrum, as well as explosive materials such as TNT, which also can be probed for detection of air pollution [3] or in stand-off ranged detection of hazardous materials [4], respectively.…”

Advances in explosives analysis—part II: photon and neutron methods

“…Although diffuse scattering of thermal IR sources off the sample can aid in spectral acquisition [59,60,64], the collimation and power on-target for laser sources is far greater. Femtosecond optical parametric oscillators [65] and tunable carbon dioxide lasers [66] have been used as spectroscopic IR sources, but most research is currently focused on illumination by tunable quantum cascade lasers (QCLs). Active QCL illumination coupled with array detectors enables hyperspectral imaging that can match the spectrum of residues with library spectra of explosives ( Fig.…”

Stand-Off Chemical Detection Using Photoacoustic Sensing Techniques—From Single Element to Phase Array

“…For example, Raman spectroscopy, a single-shot measurement [12], has relatively low photon generation efficiency due to its nonlinear nature and uses high power pulsed lasers in the UV or short-visible wavelength ranges, which raises eye-safety concerns. Another example would be thermal imaging techniques [13,14] that require expensive mid-IR cameras, exhibits lower sensitivity than near-IR detectors, and can easily saturate with rising ambient temperature thereby depreciating the desired accuracy and becoming difficult to use. Furthermore, PA sensing's signal strength is inversely proportional to R, where R is radius with the target chemical as the center.…”