Proceedings Article | 5 May 2012
Proc. SPIE. 8358, Chemical, Biological, Radiological, Nuclear, and Explosives (CBRNE) Sensing XIII
KEYWORDS: Telescopes, Potassium, Standoff detection, Glasses, Luminescence, Raman spectroscopy, Laser induced breakdown spectroscopy, Aluminum, Explosives, Pulsed laser operation
The University of Hawaii has been developing portable remote Raman systems capable of detecting chemicals in
daylight from a safe standoff distance. We present data on standoff detection of chemicals used in the synthesis of
homemade explosives (HME) using a portable standoff Raman system utilizing an 8-inch telescope. Data show that
good-quality Raman spectra of various hazardous chemicals such as ammonium nitrate, potassium nitrate, potassium
perchlorate, sulfur, nitrobenzene, benzene, acetone, various organic and inorganic chemicals etc. could be easily obtained
from remote distances, tested up to 120 meters, with a single-pulse laser excitation and with detection time less than
1 μs. The system uses a frequency-doubled Nd:YAG pulsed laser source (532 nm, 100 mJ/pulse, 15 Hz, pulse width
10 ns) capable of firing a single or double pulse. The double-pulse configuration also allows the system to perform
standoff LIBS (Laser-Induced Breakdown Spectroscopy) at 50 m range. In the standoff Raman detection, the doublepulse
sequence simply doubles the signal to noise ratio. Significant improvement in the quality of Raman spectra is
observed when the standoff detection is made with 1s integration time. The system uses a 50-micron slit and has spectral
resolution of 8 cm-1. The HME chemicals could be easily detected through clear and brown glass bottles, PP and HDPE
plastic bottles, and also through fluorescent plastic water bottles. Standoff Raman detection of HME chemical from a 10
m distance through non-visible concealed bottles in plastic bubble wrap packaging is demonstrated with 1 s integration
time. Possible applications of the standoff Raman system for homeland security and environmental monitoring are
discussed.
