Standoff Detection of Explosives: Infrared (IR) Spectroscopy Chemical Sensing

Download Project Report (Phase 2, Year 7)

Project Description

Overview and Significance

This project deals with the use of infrared spectroscopy in standoff mode and coupled to laser sources operating in the mid-infrared (MIR) to develop confirming (orthogonal chemical sensors) for detecting explosives residues on clothing, travel bags, personal bags, laptop bags/cases, skin and other substrates. The main hurdle to overcome is discriminating the nitro- or peroxide-based explosives from highly interfering, MIR absorbing substrates (matrices) in which explosives are found. Quantum cascade lasers (QCL) will be used as energy sources. QCL have revolutionized MIR spectroscopy applications. Techniques evaluated will provide positive/negative or a confidence level indication to the operator for the presence of explosives within 1 min (in most cases a few seconds) while operating effectively in a field environment at multiple distances with varying levels of relative humidity, air particulates, temperature, light and wind.

A main objective of the tasks performed by this research and education component at the University of Puerto Rico at Mayaguez (UPRM) is to lay the foundation for the standoff detection of explosives on highly MIR absorbing substrates, including cotton, cardboard, wood, plastics, and create a library of adaptable infrared absorbance / reflectance spectra for a variety of highly energetic materials (HEM) on various substrate surfaces. An addressable library of HEM will be built, tested and made available. The spectra in the library will be able to be modified or morphed according to models that consider the spectroscopic measurement conditions,the physical features of the HEM residues and the characteristics of the substrate surfaces. This library is intended to be useful for both the identification of single target chemicals that are combined with many clutter species as well as the discrimination among multiple target chemicals that are mixed with each other and with additional clutter species.

The library can include as many as 30 target HEM and 7 or more substrate types. Target chemicals will include high explosives, explosives formulations, non nitrogen-based, home-made explosives and co indicator compounds and precursors of these various chemicals. Substrates could be metals or non-metals and could have high infrared transmittance of reflectance or absorbance; they could also have low infrared transmittance, reflectance or absorbance.

The concentration of a given dilute solid on a surface can be 1 μg/cm2 or lower. Single target chemicals can represent as little as 0.1% of the overall residue. Mixtures can have as many as 5 to 10 target components plus 15 or more additional background chemicals, with a given target component representing as little as 1% of the overall amount of residue on a surface. Development of this library will include the preparation of samples comprising chemical residues on the surface of a substrate, spectroscopic characterization of samples like the ones prepared and the investigation and modeling of various measurement effects and residue/substrate effects. The measurements performed at UPRM will make use of several spectroscopic measurement instruments available, including an FT-IR spectrometer, tunable QCL sources and photodetectors.

Vibrational spectroscopy consists of two main techniques: infrared spectroscopy (IRS) and Raman scattering (RS). Spectra obtained by means of these techniques can be used for identifying and quantifying samples in complex matrices because each substance has a unique spectrum in the fingerprint and fundamental vibrations regions of the MIR region and corresponding Raman shift regions.
Phase 2 Year 2 Annual Report
Project Leader
  • Samuel P. Hernandez-Rivera
    University of Puerto Rico, Mayagüez

Faculty and Staff Currently Involved in Project
  • Ricardo Infante-Castillo
    DHS MSI-SRTP-2017; Follow-On Grant-2018

Students Currently Involved in Project
  • Diego A. Alejandro-Rivera
    University of Puerto Rico, Mayagüez