Mid-Infrared Laser Spectroscopy Applications I: Detection of Traces of High Explosives on Reflective and Matte Substrates

Abstract

Mid-infrared (MIR) lasers have revolutionized infrared vibrational spectroscopy, converting an already dominant spectroscopic analysis technique into an even more powerful, easier to use, and quicker turnaround cadre of versatile spectroscopic tools. A selection of applications, revisited under the umbrella of MIR laserbased properties, very high brightness, collimated beams, polarized sources, highly monochromatic tunable sources, and coherent sources, is included. Applications discussed concern enhanced detection, discrimination, and quantification of high explosives (HEs). From reflectance measurements of chemical residues on highly reflective metallic substrates to reflectance measurements of HEs deposited on non-reflective, matte substrates is discussed. Coupling with multivariate analyses (MVA) techniques of Chemometrics allowed near trace detection of HEs, with sharp discrimination from highly MIR absorbing substrates.

Mid-Infrared Laser Spectroscopy Detection and Quantification of Explosives in Soils Using Multivariate Analysis and Artificial Intelligence

“…Compared to the existing sources in the MIR range, QCL sources have a higher output power that allows remote sensing and analysis. The rapid detection of HEs on highly reflective substrates using this method was demonstrated and reported by other investigators [34][35][36][37][38]. This spectroscopic analysis can be achieved without contact and in a non-destructive way.…”

Setup and Analysis of a Mid-Infrared Stand-Off System to Detect Traces of Explosives on Fabrics

“…According to Ref. [ 29 ], this discrepancy arose from the varying reflectivity of the background material and posed a challenge to automatic data analysis. The influence of the background material was also visible in the exemplary TNT spectra on red fabric and dark-blue leatherette presented in Figure 7 a,b, respectively.…”

Chemical sensing of common microorganisms found in biopharmaceutical industries using MIR laser spectroscopy and multivariate analysis

“…However, it is crucial to acknowledge that our system employs a double-pass Grazing Angle Probe (GAP, operating at 82 ) with a scanning area of 4 mm by 40 mm, thus spanning 1.6 cm 2 , allowing for spatial averaging, which is important for non-uniform surface concentration samples (most real world, two or more component samples). This attribute is outlined in the patent entitled "Grazing Angle Probe Mount for Quantum Cascade Lasers" [18]. For the GAP system to function, light must reflect off the substrate at 82 relative to the surface normal, then bounce back at 0 for a second reflection at 82 .…”