Standoff Detection of Highly Energetic Materials Using Laser-Induced Thermal Excitation of Infrared Emission

Abstract

A laser-mediated methodology for standoff infrared detection of threat chemicals is described in this article. Laser-induced thermal emissions (LITE) from vibrationally excited residue of highly energetic material (HEM) deposited on substrates were detected remotely. Telescope-based Fourier transform infrared (FT-IR) spectroscopy measurements were carried out on substrates containing small amounts of HEM at surface concentrations of 5-200 μg/cm(2). Target substrates of various thicknesses were heated remotely using a carbon dioxide laser, and their mid-infrared (mid-IR), thermally stimulated emission spectra were recorded after heating. The telescope was configured from reflective optical elements to minimize emission losses in the mid-IR frequencies. Spectral replicas were acquired at distances from 4 to 64 m using an FT-IR interferometer at 4 cm(-1) resolution. The laser power, laser exposure times, and acquisition time of the FT-IR interferometer were adjusted to improve the detection and identification of samples. The advantages of increasing the thermal emission were easily observed in the results. The signal intensities were proportional to the thickness of the coated surface (a function of the surface concentration) as well as the laser power and laser exposure time. The limits of detection obtained for the HEM studied were 140-21 μg/cm(2) at 4 m. Detection was achieved at 64 m for a surface concentration of 200 μg/cm(2).

Artificial Intelligence Assisted Mid-Infrared Laser Spectroscopy In Situ Detection of Petroleum in Soils

“…The main objective of this study was to employ MIR laser spectroscopy using a QCL source to detect insoluble pollutants such as petroleum and its derivatives in soils by simulating contaminated areas. Matrices such as powdered mixtures and soils, in particular, are not easy to analyze by the use of back-reflection infrared spectroscopy in active mode [30][31][32][33]. Diverse soil types with various particle sizes were tested in this study.…”

“…This is affected if the analysis is carried out in a remote sensing modality [34,35]. A quadratic decrease in the signal with distance and angular dependence is experienced [33,36,37]. A QCL emits a markedly more significant number of photons per unit wavelength in comparison to a globar source.…”

“…On the other hand, traditional multivariate analysis (MVA) pattern recognition methods such as principal component analysis (PCA) and partial least squares coupled to discriminant analysis (PLS-DA), are used in conjunction with spectroscopic methods and are widely reported in the literature [33,37,49,50]. PCA is a non-supervised MVA statistical technique.…”

“…This implies that in the optimum separation into classes, Class A should be on one side of the threshold and Class B on the other side of it. In the case where the predictions provide no clear distinction between the classes, the number of false positives increases and the model is not suitable for discrimination [33,37,49,50].…”

Recent Developments in Spectroscopic Techniques for the Detection of Explosives

“…Due to the importance of rapid, automatic, and non-contact detection of explosives for homeland security and environmental safety [8], a variety of spectroscopic technologies have been employed to detect trace quantities of explosives; for example, terahertz (THz) spectroscopy [9,10], laser induced breakdown spectroscopy (LIBS) [11,12,13,14,15,16], Raman spectroscopy [17,18,19,20,21,22], ion mobility spectrometry (IMS) [23,24,25,26], nuclear magnetic resonance (NMR) [27,28,29,30], nuclear quadrupole resonance (NQR) [31,32,33], laser-induced thermal emissions (LITE) [34,35], infrared (IR) spectroscopy [36,37,38], mass spectrometry [39,40,41,42,43,44,45,46], optical emission spectroscopy (OES) [47,48], photo-thermal infrared imaging spectroscopy (PT-IRIS) [49,50,51], photoacoustic techniques [52,53,54], FT-FIR spectroscopy [55], microwave [56], and millimeter-wave [57], etc. Various electromagnetic radiations such as X-ray [58] and γ rays [59] have also been employed in explosive detection.…”