Standoff laser-based spectroscopy for explosives detection (original) (raw)
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UV gated Raman spectroscopy for standoff detection of explosives
Optical Materials, 2008
Real-time detection and identification of explosives at a standoff distance is a major issue in efforts to develop defense against so-called improvised explosive devices (IED). It is recognized that the only method, which is potentially capable to standoff detection of minimal amounts of explosives is laser-based spectroscopy. LDS technique belongs to trace detection, namely to its micro-particles variety. It is based on commonly held belief that surface contamination was very difficult to avoid and could be exploited for standoff detection. We have applied gated Raman spectroscopy for detection of main explosive materials, both factory and homemade. We developed and tested a Raman system for the field remote detection and identification of minimal amounts of explosives on relevant surfaces at a distance of up to 30 m.
Nanosecond Gated Raman Spectroscopy for Standoff Detection of Hazardous Materials
Bulletin of the Korean Chemical Society, 2014
Laser Raman spectroscopy is one of the most powerful technologies for standoff detection of hazardous materials including explosives. Supported by recent development of laser and sensitive ICCD camera, the technology can identify trace amount of unknown substances in a distance. Using this concept, we built a standoff detection system, in which nanosecond pulse laser and nanosecond gating ICCD technique were delicately devised to avoid the large background noise which suppressed weak Raman signals from the target sample. In standoff detection of explosives which have large kill radius, one of the most important technical issues is the detection distance from the target. Hence, we focused to increase the detection distance up to 54 m by careful optimization of optics and laser settings. The Raman spectra of hazardous materials observed at the distance of 54 m were fully identifiable. We succeeded to detect and identify eleven hazardous materials of liquid or solid particles, which were either explosives or chemical substances used frequently in chemical plants. We also performed experiments to establish the limit of detection (LOD) of HMX at 10 m, which was estimated to be 6 mg.
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.
Pramana
A transportable, trolley-mounted stand-off explosive material detection system based on the time-gated Raman spectroscopy was developed and tested in our laboratory. This system is capable of identifying the explosives and improvised explosive materials located up to a distance of 30 m. A frequency tripled Nd:YAG, nanosecond pulsed laser (355 nm, 6 ns) operated at 10 Hz was used as an excitation source to induce Raman spectra of explosive materials under investigation. A reflected type 200 mm aperture telescope designed using Zemax optical design software was used to collect the backscattered Raman signals. Raman signals were recorded using the gated intensified charge coupled device (ICCD) spectrograph. A LabVIEW-based data acquisition and analysis software for real-time identification of materials was developed and used. It gives audio as well as text alarm to the operator about threat identification.
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.
Defence Science Journal
The detection of hazardous chemicals, explosives, improvised explosive materials, energetic materials and their associated compounds for security screening, forensic applications and detection of unexploded ordnance is an active area of research. The results based on comprehensive experimental study and performance of time gated Raman spectroscopy (TGRS) for stand-off detection of explosives and hazardous chemicals under realistic scenario are presented. Representative results drawn from the experimental study for detection of explosives and hazardous chemicals in simulated real field scenario are given.
Standoff Raman Detection of Explosive Materials Using a Small Raman Spectroscopy System
Journal of Al-Nahrain University-Science, 2017
In this work a standoff Raman spectroscopy SRS system has been designed, assembled and tested for detecting explosives (Ammonium nitrate, Trinitrotoluene and Urea nitrate) in dark laboratory at 4 m target-telescope distance. The SRS system employs frequency doubled Nd:YAG laser at 532 nm excitation with laser power of 250 mW and integration time of 2 second. The Cassegrain telescope was coupled to the Ventana Raman spectrometer using a fiber optics cable, and Notch filter is used to reject Rayleigh scattering light. The Raman scattered light is collected by a telescope and then transferred via fiber optic to spectrometer and finally directed into charge coupled device CCD detector. In order to test SRS system, it has been used to detect the Raman spectra of Toxic Industrial Compounds TIC such as acetone, toluene, and carbon tetrachloride. The SRS results were compared with conventional Raman microscopy results using a bench top Bruker SENTERRA Raman instrument.
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.
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.
Standoff explosives trace detection and imaging by selective stimulated Raman scattering
Applied Physics Letters, 2013
We introduce a sensitive method for laser based standoff detection of chemicals based on stimulated Raman scattering. Selective excitation of a particular Raman transition is detected by measuring the diffusely reflected laser light from a distant surface. The method simultaneously measures stimulated Raman loss and gain within a single laser shot and is insensitive to the optical properties (reflectivity/absorptivity) of the substrate. We demonstrate the specificity and sensitivity by detecting and imaging nanogram analyte micro-crystals on paper, fabric, and plastic substrates at 1 to 10 m standoff distance using only 10 mW of laser power from a single femtosecond laser. V