Active mode standoff measurement using infrared spectroscopy were carried out in which the angle between target and the source was varied from 0-70° with respect to the surface normal of substrates containing traces of highly energetic materials (explosives). The experiments were made using three infrared sources: a modulated source (Mod-FTIR), an unmodulated source (UnMod-FTIR) and a scanning quantum cascade laser (QCL), part of a dispersive mid infrared (MIR) spectrometer. The targets consisted of PENT 200 μg/cm<sup>2</sup> deposited on aluminum plates placed at 1 m from the sources. The evaluation of the three modalities was aimed at verifying the influence of the highly collimated laser beam in the detection in comparison with the other sources. The Mod-FTIR performed better than QCL source in terms of the MIR signal intensity decrease with increasing angle.
Recent investigations have focused on the improvement of rapid and accurate methods to develop spectroscopic markers of compounds constituting microorganisms that are considered biological threats. Quantum cascade lasers (QCL) systems have revolutionized many areas of research and development in defense and security applications, including his area of research. Infrared spectroscopy detection based on QCL was employed to acquire mid infrared (MIR) spectral signatures of Bacillus thuringiensis (Bt), Escherichia coli (Ec) and Staphylococcus epidermidis (Se), which were used as biological agent simulants of biothreats. The experiments were carried out in reflection mode on various substrates such as cardboard, glass, travel baggage, wood and stainless steel. Chemometrics statistical routines such as principal component analysis (PCA) regression and partial least squares-discriminant analysis (PLS-DA) were applied to the recorded MIR spectra. The results show that the infrared vibrational techniques investigated are useful for classification/detection of the target microorganisms on the types of substrates studied.
An infrared spectroscopy based explosives detection system using a quantum cascade laser (QCL) as excitation source was used to record mid infrared spectral signals of highly energetic materials (HEM) deposited on real world substrates such as travel baggage, cardboard and wood. The HEMs used were nitroaromatic military explosive trinitrotoluene (TNT), aliphatic nitrate ester pentaerythritol tetranitrate (PETN) and aliphatic nitramine hexahydrotrinitrotriazine (RDX). Various deposition methods including sample smearing, spin coating, spray deposition and partial immersion were evaluated for preparing samples and standards used as part of the study. Chemometrics statistical routines such as principal component analysis (PCA) regression with various preprocessing steps were applied to the recorded infrared spectra of explosives deposited as trace contaminants on target substrates. The results show that the dispersive infrared vibrational technique investigated using QCL is useful for detection of HEMs in the types of substrates studied.
A standoff multivariate calibration for detection of highly energetic materials (HEM) using Fourier transform infrared
spectroscopy is presented in this report. The procedure consists in standoff sensing at 1 m distance and the variation of
three parameters of detection. The first variable considered was the angular dependence: 0° to 45‡ from source-target with respect to alignment of target-detector. The second variable consisted on the use of several surfaces on which the material was deposited. The substrates used were polished aluminum and anodized aluminum. The third variable studied was the dependence on some specific analyte loading surface concentration: from 10 μg/cm<sup>2</sup> to200 μg/cm<sup>2</sup>. The HEM
used in this work was PETN, synthesized in our lab. Calibration curves were based on the use of chemometrics routines
such as partial least squares (PLS) regression analysis. This algorithm was used to evaluate the impact of the angular
dependence about the limits of detection of different HME loadings on aluminum substrates.
A remote infrared spectroscopy (RIRS) detection system was assembled using a mid infrared (MIR) Fourier
Transform interferometer useful in open-path (OP) mode, a reflective infrared telescope and a cryocooled wide
band, MCT detector. The system was used for passive mode IR thermal emission measurements and was also
coupled to another Newtonian telescope in conjunction with a globar source for active mode measurements. The
operation of the system was validated by measuring RIRS spectra of gases (NH<sub>3</sub>) and condensable vapors: acetone,
dichloromethane, methyl ether and acetonitrile. Solid samples were measured by smearing small amounts on
aluminum plates after dissolving in appropriate solvents. Highly energetic compounds: TNT, DNT, PETN and RDX
were also detected. Experiments of solids on metal surfaces were carried out in passive and active modes. The
analyzed samples were placed at different standoff distances up to a maximum of 30 m in active mode and 60 m in
Spectroscopy based standoff detection systems: Raman and FTIR have been tested for detection of threat chemicals,
including highly energetic materials, homemade explosives, explosives formulations and high explosives mixtures.
Other threat chemicals studied included toxic industrial compounds (TIC) and chemical agent simulants.
Microorganisms and biological threat agent simulants have also been detected at standoff distances. Open Path FTIR
has been used to detect vapors and chemicals deposited on metal surfaces at μg/cm<sup>2</sup> levels at distances as far as 30
m in active mode and 60 m in passive mode. In the case of Raman telescope, standoff distances for acetonitrile and
ammonium nitrate were 140 m.