Standoff Raman Detection of Explosive Materials Using a Small Raman Spectroscopy System (original) (raw)
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Detection of Trace Explosive Materials by Standoff Raman Spectroscopy System
Journal of Al-Nahrain University-Science, 2017
Standoff Raman spectroscopy SRS technique is one of the most powerful technologies that can identify trace amount of explosive materials. The Raman scattered signal collected by reflective telescope and a spectrograph is used to analyze the Raman scattered light. In order to view the spectrum, the spectrograph is equipped with charge coupled device CCD detector which allows detection of very weak stokes line. In order to test the capability of SRS system of detecting explosives trace, detection of C4 and AN explosives have been achieved with limit of detection (LOD) about 20 µg for C4 and 40 µg for AN.
Remote Raman and Infrared Spectroscopy Detection of High Explosives
The remote detection of highly energetic materials (HEM) based on vibrational spectroscopy is an important topic to include in the review of the classification, composition and properties of explosives. Infrared and Raman spectroscopies allow for the detection and remote identification of chemicals and biological threats and also enable the use of chemometrics for enhanced detection and discrimination. An IR system was configured by coupling an ―open path‖ FTIR interferometer to a reflective IR telescope (for passive detection) and to a telescope coupled mid-IR source (for active detection). The RRS instrument was built by fiber coupling a spectrograph to a reflective telescope. HEM samples were detected on stainless steel surfaces as thin films (50-3400 g/cm2) for IR experiments and as particles (3-85 mg) for Raman measurements. Nitroaromatic HEMs, including TNT, DNT and RDX; HEM formulations, including C4 and Semtex-H; inorganic HEM (ammonium nitrate) and acetone peroxides (TATP)...
Remote Raman spectroscopy of explosive precursors
Optical Engineering
Deep ultraviolet Raman spectroscopy measurements have been performed at the German Aerospace Center (DLR) with the aim of detecting traces (μg range) of explosive precursors. In this study, a backscattering Raman system was setup and optimized to detect urea, sodium perchlorate, ammonium nitrate, and sodium nitrate at a 60-cm short-range remote detection. The sample was tested at 264-nm ultraviolet laser excitation wavelength to experimentally observe any possible trace over textiles samples. For each colored sample textile, Raman spectra were acquired and no background fluorescence interference was observed at this laser excitation wavelength. Detection limits and system sensitivity with an acquisition time up to 3 s for microgram traces are presented. © The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.
Stand-off detection of explosives particles by multispectral imaging Raman spectroscopy
Applied Optics, 2011
A Raman multispectral imaging technique is presented, which can be used for stand-off detection of single explosives particles. A frequency-doubled Nd:YAG laser operating at 10 Hz illuminates the surface under investigation. The backscattered Raman signal is collected by a receiver subsystem consisting of a 150 mm Schmidt-Cassegrain telescope, a laser line edge filter, a liquid-crystal tunable filter, and a gated intensified charge-coupled device (ICCD) detector. A sequence of images is recorded by the ICCD, where, for each recording, a different wavelength is selected by the tunable filter. By this, a Raman spectrum is recorded for each pixel, which makes it possible to detect even single particles when compared to known spectra for possible explosives. The comparison is made using correlation and least-square fitting. The system is relatively insensitive to environment and light variations. Multispectral Raman images of sulfur, ammonium nitrate, 2,4-dinitrotoluene, and 2,4,6-trinitrotoluene were acquired at a stand-off distance of 10 m. Detection of sulfur particles was done at a distance of 10 m.
Applied Physics B, 2016
spectroscopies, which are considered as most appealing means. For instance, Raman spectroscopy [5, 11-25] and its coherent variants, coherent anti-Stokes Raman scattering (CARS) [26-32] and stimulated Raman scattering (SRS) [33] have been used for explosives detection over large or short distances. These methods, based on spontaneous or coherent Raman scattering, provide relatively sharp spectral features in a broad spectral range, leading to signatures that are strongly related to specific compounds and to their spatial distribution, and ultimately allowing explosives identification, even on strongly interfering surfaces. While standoff detection was mainly used for identification of bulk quantities of explosives or of single large particles, positioned on distant targets, the point and proximal detection focused on uncovering the presence of single particles or of particles residing from fingerprints. Detection of these residues on a variety of substrates (glass, metals and clothing) was achieved using integrated tabletop microscope-based Raman systems [20-22] or a homebuilt compact system [23-25]. These approaches were used not only for measurement of Raman spectra, but also for Raman imaging of explosives residues. Imaging was achieved by point-mapping, involving laser spot or sample raster-scanning through the x and y spatial dimensions, and resulting in successive Raman spectra at each particular x, y position. The drawback of this approach is that it is extremely time-consuming. Consequently, obtaining even moderate-size Raman images, while operating the system with short integration times for each measurement point, can take several hours [23]. For instance, mapping of a 1 × 1 cm sample of potassium nitrate (KNO 3) particles, with 50 μm steps, by the compact Raman spectrometer took 8 h [24]. Essentially, by photographing the sample, prior to data acquisition, it was possible to selectively monitor spatially resolved particles Abstract Measurements of Raman scattering spectra and of Raman maps of particles of explosives and related compounds [potassium nitrate, 2,4-dinitrotoluene (DNT), 2,4,6-trinitrotoluene (TNT) and 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX)] were performed by a homebuilt compact Raman system, functioning with a 532-nm laser beam, focused as a point or line, along with full vertical binning or image readout of an intensified charge-coupled device camera. High specificity and sensitivity were obtained by line-excitation, which allowed fast detection and mapping of explosive particles with a relatively simple system.
Subsurface Sensing Technologies and Applications, 2010
This study describes the design, assembly, testing and comparison of two Remote Raman Spectroscopy (RRS) systems intended for standoff detection of hazardous chemical liquids. Raman spectra of Chemical Warfare Agents Simulants (CWAS) and Toxic Industrial Compounds (TIC) were measured in the laboratory at a 6.6 m source-target distance using continuous wave (CW) laser detection. Standoff distances for pulsed measurements were 35 m for dimethyl methylphosphonate (DMMP) detection and 60, 90 and 140 m for cyclohexane detection. The prototype systems consisted of a Raman spectrometer equipped with a CCD detector (for CW measurements) and an I-CCD camera with time-gated electronics (for pulsed laser measurements), a reflecting telescope, a fiber optic assembly, a single-line CW laser source (514.5, 488.0, 351.1 and 363.8 nm) and a frequency-doubled single frequency Nd:YAG 532 nm laser (5 ns pulses at 10 Hz). The telescope was coupled to the spectrograph using an optical fiber, and filters were used to reject laser radiation and Rayleigh scattering. Two quartz convex lenses were used to collimate the light from the telescope from which the telescope-focusing eyepiece was removed, and direct it to the fiber optic assembly. To test the standoff sensing system, the Raman Telescope was used in the detection of liquid TIC: benzene, chlorobenzene, toluene, carbon tetrachloride, cyclohexane and carbon disulfide. Other compounds studied were CWAS: dimethylmethyl phosphonate, 2-chloroethyl ethyl sulfide and 2-(butylamino)-ethanethiol. Relative Raman scattering cross sections of liquid CWAS were measured using single-line sources at 532.0, 488.0, 363.8 and 351.1 nm. Samples were placed in glass and quartz vials at the standoff distances from the telescope for the Remote Raman measurements. The mass of DMMP present in water solutions was also quantified as part of the system performance tests.
Challenges, 2016
Surface-enhanced Raman spectroscopy (SERS) measurements of some common military explosives were performed with a table-top micro-Raman system integrated with a Serstech R785 miniaturized device, comprising a spectrometer and detector for near-infrared (NIR) laser excitation (785 nm). R785 was tested as the main component of a miniaturized SERS detector, designed for in situ and stand-alone sensing of molecules released at low concentrations, as could happen in the case of traces of explosives found in an illegal bomb factory, where solid microparticles of explosives could be released in the air and then collected on the sensor's surface, if placed near the factory, as a consequence of bomb preparation. SERS spectra were obtained, exciting samples in picogram quantities on specific substrates, starting from standard commercial solutions. The main vibrational features of each substance were clearly identified also in low quantities. The amount of the sampled substance was determined through the analysis of scanning electron microscope images, while the spectral resolution and the detector sensitivity were sufficiently high to clearly distinguish spectra belonging to different samples with an exposure time of 10 s. A principal component analysis procedure was applied to the experimental data to understand which are the main factors affecting spectra variation across different samples. The score plots for the first three principal components show that the examined explosive materials can be clearly classified on the basis of their SERS spectra.
Standoff Raman Spectroscopy of C4 Explosive and Study the Effect of Integration Time and Laser Power
Journal of Al-Nahrain University-Science, 2017
In this paper standoff Raman spectroscopy SRS system for explosive materials is developed. Standoff Raman detection of C4 substance under dark laboratory condition at 4 m distance is achieved. A frequency doubled Nd:YAG laser at 532 nm excitation is used. The Raman scattered light is collected by a telescope and then transferred via fiber optics cable to spectrograph and finally into CCD detector. Notch filter used to reject Rayleigh scattering light. Carbon tetrachloride CCL 4 and Acetone (CH 3) 2 CO are used as a calibration standard for the Raman measurements because of their strong and intensive scattering capability. Raman measurement of C4 explosive is also acquired using conventional Raman microscopy for verification of standoff Raman measurements. The effects of integration time and laser power on Raman cross section under dark condition were studied. Standoff Raman detection of C4 substance at 4 m distance under partially illuminated condition has been achieved and hence the effect of higher integration time was studied under the same condition.
Demonstrated Wavelength Portability of Raman Reference Data for Explosives and Chemical Detection
2012
As Raman spectroscopy continues to evolve, questions arise as to the portability of Raman data: dispersive versus Fourier transform, wavelength calibration, intensity calibration, and in particular the frequency of the excitation laser. While concerns about fluorescence arise in the visible or ultraviolet, most modern (portable) systems use near-infrared excitation lasers, and many of these are relatively close in wavelength. We have investigated the possibility of porting reference data sets from one NIR wavelength system to another: We have constructed a reference library consisting of 145 spectra, including 20 explosives, as well as sundry other compounds and materials using a 1064 nm spectrometer. These data were used as a reference library to evaluate the same 145 compounds whose experimental spectra were recorded using a second 785 nm spectrometer. In 128 cases of 145 (or 88.3% including 20/20 for the explosives), the compounds were correctly identified with a mean "hit score" of 954 of 1000. Adding in criteria for when to declare a correct match versus when to declare uncertainty, the approach was able to correctly categorize 134 out of 145 spectra, giving a 92.4% accuracy. For the few that were incorrectly identified, either the matched spectra were spectroscopically similar to the target or the 785 nm signal was degraded due to fluorescence. The results indicate that imported data recorded at a different NIR wavelength can be successfully used as reference libraries, but key issues must be addressed: the reference data must be of equal or higher resolution than the resolution of the current sensor, the systems require rigorous wavelength calibration, and wavelength-dependent intensity response should be accounted for in the different systems.
Classification of Raman Spectra to Detect Hidden Explosives
IEEE Geoscience and Remote Sensing Letters, 2000
Raman spectroscopy is a laser-based vibrational technique that can provide spectral signatures unique to a multitude of compounds. The technique is gaining widespread interest as a method for detecting hidden explosives due to its sensitivity and ease of use. In this letter, we present a computationally efficient classification scheme for accurate standoff identification of several common explosives using visible-range Raman spectroscopy. Using real measurements, we evaluate and modify a recent correlation-based approach to classify Raman spectra from various harmful and commonplace substances. The results show that the proposed approach can, at a distance of 30 m, or more, successfully classify measured Raman spectra from several explosive substances, including nitromethane, trinitrotoluene, dinitrotoluene, hydrogen peroxide, triacetone triperoxide, and ammonium nitrate.