F2-F Remote Raman and Infrared Detection of Explosives and Other Threat Agents

Abstract:The objective of this work is to develop new technologies and extend the existing technologies based on Remote Raman Spectroscopy (RRS) and Remote Infrared Spectroscopy (RIRS) as applied to detection of highly energetic materials (HEM). The pursued enhancements are based on: 1) improving range detection (distances greater than 100 meters), 2) lowering current detection limits, and 3) detecting Raman signatures of realistic explosives-related materials for eventual detection of Improvised Explosive Devices (IEDs) and homemade explosives (HME). Applications of technologies under development will contribute significantly to the solution of the problems related to remote detection of hazardous chemicals, including HEM, chemical warfare agents (CWA) and toxic industrial compounds (TIC). The methodologies to be developed will enable detection of small amounts of chemicals, their formulations and their degradation products. The techniques based on RRS detection are non-invasive, rapid and real-time or nearly so (<1m). Remote detection at distances of more than 50 meters had been previously attained by several researchers, but through this effort target-collector distances of > 140 m have already successfully been achieved. The work addresses advancing the instrumentation by designing optimized versions of visible (VIS) and near infrared (NIR) Raman Telescopes. The issue of selectivity and interferences will be addressed in Year 3, as well as other issues that can be used for prediction of spectral signals (signatures and sensitivity) of environmentally exposed HEM. The outcome of these studies will be a better understanding of the chemical signatures from exposed HEM and the ability to predict the performance of spectroscopic measurement techniques for measuring many different types of energetic materials.

In Year 2, telescope-enabled, Fourier Transform infrared spectroscopy (FTIR) in the form of �open path� detection experiments, both looking at thermally excited emissions (passive mode) and stimulated emissions (active mode), was started. Experiments include remote IR spectroscopy detection of TNT deposited on metallic substrates (50-400 mg/cm2) at standoff distances of 4-30 m using a telescope coupled mid IR source. Passive mode detection included thermal excitation by quartz-halogen lamp, simulating explosive traces deposited on metal surfaces exposed to sunlight heating. Year 3 work will include laser thermal excitation of samples and modeling to determine local temperature and data analysis using �Extended Multiplicative Signal Correction� for on the fly water vapor and reflective band shape distortions compensation, in collaboration with M. Diem (Northeastern U.) and M. Velez (Univ. PR-Mayaguez).

In collaboration with P. Chen (Spelman College), a series of high resolution coherent 2D spectroscopy experiments over a wavelength range of >150 nm were conducted in order to determine the feasibility of using resonantly enhanced coherent Raman spectroscopy to detect NO2 that is released when nitrogenbased explosives are illuminated by UV light. One purpose of this study was to determine the optimum laser and detection wavelengths for setting up a remote coherent Raman system that is NO2 specific. A second purpose of this study was to assess the effect of dephasing caused by air molecules on the resonantly enhanced coherent Raman signal from NO2. The findings of this study indicates that resonantly enhanced coherent Raman spectroscopy is not feasible for detecting NO2 in air, but that it may be feasible for detecting other species (e.g., direct detection of nitrogen-based explosives). Furthermore, although resonantly-enhanced signals (CARS) are too severely dephased by air molecules, conventional (non-enhanced) coherent Raman signals are not severely dephased and can be used to detect NO2 in air. Therefore, two future directions are suggested: determination of whether the detection limits using conventional CARS is sufficient for detecting UV-illuminated nitrogen-based explosives, and future studies involving direct detection of specific explosives.

Faculty and Staff Currently Involved in Project:

Samuel P. Hernandez-Rivera
Professor
University of Puerto Rico at Mayagüez

Miguel Velez
Professor
University of Puerto Rico at Mayagüez

Max Diem
Professor
Northeastern University

Peter C. Chen
Professor
Spelman College

Students Currently Involved in Project:

Leonardo C. Pacheco, Ph.D.
University of Puerto Rico at Mayagüez

Hilsamar Felix, Ph.D.
University of Puerto Rico at Mayagüez

William Ortiz, Ph.D.
University of Puerto Rico at Mayagüez

Oliva M. Primera, Ph.D.
University of Puerto Rico at Mayagüez

John R. Castro, M.S.
University of Puerto Rico at Mayagüez

Justin Perry, B.S.
Morehouse College

Shannon Belle, B.S.
Spelman College

Kamilah Mitchell, B.S.
Spelman College