Compact standoff Raman system for detection of homemade explosives

Abstract

We present data on standoff detection of chemicals used in synthesis of homemade explosives (HME) using a compact portable standoff Raman system developed at the University of Hawaii. Data presented in this article show that good quality Raman spectra of various organic and inorganic chemicals, including hazardous chemicals such as ammonium nitrate, potassium nitrate, potassium perchlorate, sulfur, nitrobenzene, benzene, acetone, and gasoline, can be easily obtained from remote distances with a compact standoff Raman system utilizing only a regular 85 mm Nikon camera lens as collection optics. Raman spectra of various chemicals showing clear Raman fingerprints obtained from targets placed at 50 m distance in daylight with 1 to 10 second of integration time are presented in this article. A frequencydoubled mini Nd:YAG pulsed laser source (532 nm, 30 mJ/pulse, 20 Hz, pulse width 8 ns) is used in an oblique geometry to excite the target located at 50 m distance. The standoff Raman system uses a compact spectrograph of size 10 cm (length) x 8.2 cm (width) x 5.2 cm (height) with spectral coverage from 100 to 4500 cm -1 Stokes-Raman shifted from 532 nm laser excitation and is equipped with a gated thermo-electrically cooled ICCD detector. The system is capable of detecting both the target as well as the atmospheric gases before the target. Various chemicals could be easily identified through glass, plastic, and water media. Possible applications of the standoff Raman system for homeland security and environmental monitoring are discussed.

Single-Pulse Standoff Raman Detection of Chemicals from 120 m Distance during Daytime

“…There are five different crystalline phases (phases I to V) of NH 4 NO 3 reported in the literature, each stable over a different temperature range. 31,–33 At typical room temperature (anywhere between −18 and 32 °C), the stable phase of NH 4 NO 3 is phase IV, 33 which is shown in Fig. 3.…”

“…The Raman peaks at 715 cm −1 and between 50 and 250 cm −1 are, respectively, the in-plane bending ( v 4 ) vibrations of the NO 3 − ion, and the lattice (translational and rotational) vibrations of the NO 3 − and NH 4 + ions. 32,33…”

Optimizing Data Reduction Procedures in Spatial Heterodyne Raman Spectroscopy with Applications to Planetary Surface Analogs

“…The accumulation time was 10 s. The peak positions of the main Raman lines of these salts are in agreement with the values reported in the literature. 42–43 The key features of the Raman spectra presented in this figure are the symmetric stretches (ν 1 ) of the anion that appear as strong Raman lines at 937, 940, and 1048 cm −1 for KClO 3 , KClO 4 , and KNO 3 , respectively. Other key features include the symmetric bending (ν 2 ) of the anion that appears at 487 and 463 cm −1 for KClO 3 and KClO 4 , respectively, and the antisymmetric bend (ν 4 ) that appears as weak Raman lines at 617, 630, and 716 cm −1 for KClO 3 , KClO 4 , and KNO 3 , respectively.…”

Passive delivery of mixed explosives vapor from separated components

“…Remote as well as proximate detection capabilities, detection through packaging or a container, and detection of both bulk and trace quantities are also necessary. Additionally, detection systems must be fast, robust, and selective with a low rate of false alarms [3,6,7].…”