title: Standoff detection of high explosive materials at 50 meters in ambient light conditions using a small Raman instrument.
abstract: We have designed and demonstrated a standoff Raman system for detecting high explosive materials at distances up to 50 meters in ambient light conditions. In the system, light is collected using an 8-in. Schmidt-Cassegrain telescope fiber-coupled to an f/1.8 spectrograph with a gated intensified charge-coupled device (ICCD) detector. A frequency-doubled Nd : YAG (532 nm) pulsed (10 Hz) laser is used as the excitation source for measuring remote spectra of samples containing up to 8% explosive materials. The explosives RDX, TNT, and PETN as well as nitrate- and chlorate-containing materials were used to evaluate the performance of the system with samples placed at distances of 27 and 50 meters. Laser power studies were performed to determine the effects of laser heating and photodegradation on the samples. Raman signal levels were found to increase linearly with increasing laser energy up to approximately 3 x 10(6) W/cm2 for all samples except TNT, which showed some evidence of photo- or thermal degradation at higher laser power densities. Detector gate width studies showed that Raman spectra could be acquired in high levels of ambient light using a 10 microsecond gate width.
authors.affiliation: Lawrence Livermore National Laboratory, M division/Forensic Science Center, 7000 East Ave, L-178, Livermore, California 94550, USA. carter45@llnl.gov
authors.forename: J Chance
authors.initials: JC
authors.lastname: Carter
authors.forename: S Michael
authors.initials: SM
authors.lastname: Angel
authors.forename: Marion
authors.initials: M
authors.lastname: Lawrence-Snyder
authors.forename: Jon
authors.initials: J
authors.lastname: Scaffidi
authors.forename: Richard E
authors.initials: RE
authors.lastname: Whipple
authors.forename: John G
authors.initials: JG
authors.lastname: Reynolds
mesh_terms: D004784:Environmental Monitoring / Q000295:instrumentation / Q000379:methods; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005107:Explosions / Q000517:prevention & control; D055095:Optics and Photonics / Q000295:instrumentation*; D010417:Pentaerythritol Tetranitrate / Q000032:analysis*; D012637:Security Measures; D013059:Spectrum Analysis, Raman / Q000295:instrumentation*; D023481:Terrorism / Q000517:prevention & control*; D014227:Triazines / Q000032:analysis*; D014303:Trinitrotoluene / Q000032:analysis*
chemical_list: D014227:Triazines; D010417:Pentaerythritol Tetranitrate; D014303:Trinitrotoluene; C009160:cyclonite