Infrared hyperspectral standoff detection of explosives

Abstract

In this work we demonstrate imaging standoff detection of solid traces of explosives using infrared laser backscattering spectroscopy. Our system relies on active laser illumination in the 7 µm-10 µm spectral range at fully eye-safe power levels. This spectral region comprises many characteristic absorption features of common explosives, and the atmospheric transmission is sufficiently high for stand-off detection. The key component of our system is an external cavity quantum cascade laser with a tuning range of 300 cm(-1) that enables us to scan the illumination wavelength over several of the characteristic spectral features of a large number of different explosives using a single source. We employ advanced hyperspectral image analysis to obtain fully automated detection and identification of the target substances even on substrates that interfere with the fingerprint spectrum of the explosive to be detected due to their own wavelength-dependent scattering contributions to the measured backscattering spectrum. Only the pure target spectra of the explosives have to be provided to the detection routine that nevertheless accomplishes reliable background suppression without any a-priory-information about the substrate

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

“…Active QCL illumination coupled with array detectors enables hyperspectral imaging that can match the spectrum of residues with library spectra of explosives ( Fig. 3) [67][68][69][70]. The backscattering collected is a strong function of the angle of incidence, but the contrast in spectral features has been observed to remain with orders of magnitude less signal than specular reflection [64,71].…”

Recent Advances and Applications of External Cavity-QCLs towards Hyperspectral Imaging for Standoff Detection and Real-Time Spectroscopic Sensing of Chemicals

“…Backscattering images illuminated by the EC-QCL at different wavelengths were recorded here from a close distance of~1 m. Comparison to other samples with known amount of material and visual inspection suggested that the illuminated area contained a total amount of TNT on the order of 100 µg. Previous publications showed that over distances of a few meters, quantitates down to 10 µg are detectable [33]. The backscattering spectrum of jeans denim strongly resembles that of TNT, so false alarms or interferences might be expected.…”

High sensitivity stand-off detection and quantification of chemical mixtures using an active coherent laser spectrometer (ACLaS)

“…Instruments can be operated in a "point and shoot" mode using a single pixel detector or in an imaging configuration using a detector array. This second mode has been successfully applied to the detection of solid and liquid contaminants on surfaces 6,7,8 .…”

“…Substituting Equation 4 into Equation 5, the retrieved state appears as a function of the true one as expressed in Equation 6.…”

“…5) Eye-safe operation: operational laser spectrometers deployed in public open areas should meet laser emission limits for a class 1 laser and must pose no risk of harm to the public. 6) Compact and portable design: weight, power requirements and physical size are key aspects to enhance the deployment capability of a stand-off detection system. Ultimately, a portable or hand-held device would be extremely desirable.…”