Compact standoff Raman system for detection of homemade explosives

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 frequency-doubled 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.