Enhanced RDX Detection Studies on Various Types of Substrates via Tunable Quantum Cascade Laser Spectrometer Coupled with Grazing Angle Probe

Abstract

Owing to scientific advances in the field of materials sciences and engineering, researchers have developed new energy sources used for spectroscopic applications and measurements of properties resulting from the interaction of matter and electromagnetic radiation in the mid-infrared (MIR) region. MIR lasers, such as quantum cascade lasers (QCLs), used for spectroscopy have quickly found numerous applications in a wide cadre of IR techniques. This provides the opportunity to study properties of highly energetic materials (HEM), among many other applications. MIR laser spectroscopy based detection experiments of HEMs were carried out using a QCL optically coupled to compact grazing angle probe mount (QCL-GAP) enabling reflection-absorption infrared spectroscopy (RAIRS) measurements of thin films of HEMs. A saturated solution of RDX in acetone was prepared, and aliquots of subsequent dilutions of the stock solutions were transferred to test surfaces for QCL-GAP back-reflectance measurements. RDX reflectance signals were monitored as function as the decreasing surface concentration until the signal/noise was ∼ 3. Stainless steel (SS) plates were used as reflective substrates, and anodized aluminum (AN-Al), cardboard, and Teflon were used as non-reflective (matte) substrates. Using generated calibration curves a low limit of detection (LOD) of 1.7 ng/cm2 for RDX/SS and 95 μg/cm2 for RDX/AN-Al were found. Based on the area of laser spot (0.3 cm2) we conclude the minimum masses detected were 490 pg (RDX/SS) and 28 μg (RDX/AN-Al).

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.…”

Surface Persistence of Trace Level Deposits of Highly Energetic Materials

“…Figure 2d shows the decay of the IR signals for RDX. The behavior of the area for the band at 1264 cm−1 and the band at 1321 cm−1 (N–NO2 symmetrical stretching [43,44,45,46,47,48]) vs. time are approximately linear. However, the IR intensity decay vs. time is exponential for the 1593 cm−1 band (N–NO2 asymmetrical stretching [43,44,45]).…”

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

“…At 1000 cm −1 , the laser output was significantly lower (see Figure 2 ), which resulted in a decreased signal-to-noise ratio in that region. The differences in peak positions between the spectra of the printed samples and the powder sample between 1250 and 1350 cm −1 were attributed to the presence of different crystal structures of -RDX and -RDX, which are known to show differences in their infrared spectra [ 27 , 28 ]. To allow for the correct classification in special cases like this, the spectra of both crystal structures had to be included in the classification model.…”