Anti-Stokes Raman Spectrometry with 1064-nm Excitation: An Effective Instrumental Approach for Field Detection of Explosives

Abstract

Anti-Stokes Raman spectra of 28 explosive materials were obtained with 1064-nm excitation using fiber-optic sampling and a dispersive spectrograph equipped with a charge-coupled device (CCD) array detector. By using a silicon CCD detector, anti-Stokes features could clearly be observed for the majority of samples from -250 to -1650 cm(-1). Using the fiber-optic probe, spectra were routinely obtained from samples positioned up to twelve meters from the spectrograph within 240 s. The utility of an anti-Stokes correction routine is demonstrated, which routine allowed anti-Stokes spectra measured with 1064-nm excitation to be successfully searched and identified against libraries of Stokes spectra obtained using a Fourier transform (FT) Raman system equipped with a 1064-nm Nd:YAG laser.

Denoising of spectra with no user input: a spline‐smoothing algorithm

“…two different spectra taken of the same compound under the same conditions) makes them more similar to each other. In order to quantify this similarity, a hit quality index (HQI) was defined, [29] which treats each spectrum as a large vector in a high-dimensional space. By determining the dot product of this vector with the vector of a supposedly identical spectrum and normalizing it to unity, it is possible to quantify how alike the two spectra really are.…”

Evaluation of a dispersive Raman spectrometer with a Ge array detector and a 1064nm laser for the study of explosives

“…The Raman spectrum of a strongly Raman scattering explosive, TATB, obtained with the current instrumental set-up is compared to that obtained with several other alternative approaches [21,22,31] in Fig. 2.…”

“…The spectra reported in this paper have not been corrected for instrument response. For comparative purposes, the data measured with this Raman spectrometer are compared to spectra of the same samples measured on both a 830 nm CCD-based spectrometer, our 1064 nm anti-Stokes-based CCD spectrometer [31] and a standard FT-Raman spectrometer with a Nd:YAG laser and an InGaAs detector.…”

“…In a recent study, we investigated the application of antiStokes Raman spectrometry with 1064 nm excitation and detection with a silicon-based CCD array detector as a potential alternative to established CCD and FT-Raman spectrometers for the study of explosives [31]. In this paper we describe the results obtained with a no-moving parts dispersive Stokes Raman spectrometer with a Ge array detector and 1064 nm excitation for the study of explosives.…”

Recent Advances in Trace Explosives Detection Instrumentation

“…Lewis et al, have compared Raman spectra of a variety of energetic materials at three different excitation wavelengths: 785, 830 and 1064 nm [116]. For the 1064 nm excitation, anti-Stokes Raman spectra were recorded [117]. The signal to noise and Raman peak to fluorescence intensities were measured in each material at each excitation wavelength, with the conclusion that 830 nm excitation is the best compromise for a field-portable instrument.…”