Proceedings Article | 3 June 2011
Proc. SPIE. 8018, Chemical, Biological, Radiological, Nuclear, and Explosives (CBRNE) Sensing XII
KEYWORDS: Standoff detection, Explosives detection, Deep ultraviolet, Spectroscopy, Argon ion lasers, Polarizers, Raman spectroscopy, Directed energy weapons, Explosives, Algorithm development
Deep-ultraviolet resonance Raman spectroscopy (DUVRRS) is a potential candidate for stand-off detection of
explosives. A key challenge for stand-off sensors is to distinguish explosives, with high confidence, from a myriad of
unknown background materials that may have interfering spectral peaks. To address this, we have investigated a new
technique that simultaneously detects Raman spectra from multiple DUV excitation wavelengths. Due to complex
interplay of resonant enhancement, self-absorption and laser penetration depth, significant intensity variation is observed
between corresponding Raman bands with different excitation wavelengths. These variations with excitation wavelength
provide a unique signature that complements the traditional Raman signature to improve specificity relative to singleexcitation-
wavelength techniques. We have measured these signatures for a wide range of explosives using amplitudecalibrated
Raman spectra, obtained sequentially by tuning a frequency-doubled Argon laser to 229, 238, 244 and 248
nm. For nearly all explosives, these signatures are found to be highly specific. An algorithm is developed to quantify
the specificity of this technique. To establish the feasibility of this approach, a multi-wavelength DUV source, based on
Nd:YAG harmonics and hydrogen Raman shifting, and a compact, high throughput DUV spectrometer, capable of
simultaneous detection of Raman spectra in multiple spectral windows, are being investigated experimentally.
