Near Real‐Time Standoff Detection of Explosives in a Realistic Outdoor Environment at 55 m Distance

Abstract

Standoff identification of explosives at distances of up to 55 m has been performed by applying spontaneous Raman spectroscopy. This work has been focused on detection in a realistic environment, using an outdoors test field and performing experiments under varying weather conditions such as rain‐ or snowfall or bright sunshine. The instrumentation, based on a 532 nm pulsed laser source combined with gated detection, proved the performance insensitive to weather variations. Investigated HMEs and precursors were TATP, HMTD, HP, MEKP, NM, NB, and IPN; all in bulk quantities. The time needed for acquiring spectra was typically between single pulse (5 ns) and 10 s. Detection through green and brown glass bottles and PET bottles were tried and found viable.

Nanosecond Gated Raman Spectroscopy for Standoff Detection of Hazardous Materials

“…In Figure 4(f), The strongest peak of nitrobenzene was conspicuous at 1334 cm . The peak intensity was much higher that the one reported previously by Pettersson et al 4 All the secondary peaks around it were clearly detectable, albeit weaker than 30 m, in case of 54 m data.…”

“…There were some standoff Raman systems previously reported in other researches. [3][4][5] Not like most of these systems which adopted modification of retail telescope originally devised for visible observation, our system was optimally designed solely for Raman scattering detection. The positioning of lenses was chosen for effective concentration of Raman photons regarding laser beam width and expected scattering cross section.…”

A new eye-safe UV Raman spectrometer for the remote detection of energetic materials in fingerprint concentrations: Characterization by PCA and ROC analyzes

“…has greatly improved the limit of detection of the Raman instruments allowing for proximal (sample-to-device distance of some meters) or stand-off (sample-to device distance of some tenths or hundreds of meters) applications [8][9][10][11].…”

“…To our knowledge, stand-off Raman devices meeting this fundamental security criterion are still missing, or under development, so, despite the systems currently developed exhibit high sensitivity, being capable of detect explosives at distances up to hundreds meters [9,10] they cannot be used in public areas such as train stations, subways, airports, or simply outdoor in unrestricted areas, to monitor potential terrorists illegally transporting explosives. This is actually the context we considered developing our stand-off Raman detector.…”

“…Typically this is accomplished exciting the sample with high power lasers [9,10] or with lasers emitting in the near, middle ultraviolet region of the spectrum (200-400 nm) [11,12]. This wavelength range is chosen because the Raman cross section of a molecule is dependent on the excitation wavelength and scales as λ À 4 [11][12][13], therefore, the signal and the signal-to-noise ratio is increased up to some orders of magnitude when exciting in the UV region compared to the VIS excitation [12].…”