Ultrashort Pulsed Laser Vaporization Detection of Energetic Compounds
Abstract
Detection of residual signatures on or near an explosive device placed in a littoral zone is a major challenge. Typically, the low vapor pressure of explosive signatures precludes the use of vapor phase detection methods. Transferring such signatures into the gasphase would make vapor phase detection methods accessible as a means to identify and classify potential threats. Non-resonant ultrashort pulsed laser (USPL) vaporization is a universal method for transferring intact molecules from a surface into the gas phase forsubsequent mass analysis. Explosive materials including dinitrotoluene (DNT), ammonium nitrate/fuel oil (ANFO), chlorates, perchlorates, and black power formulations have been classified using this technology. USPL vaporization is universal because desorption canbe achieved from any surface due to the non-resonant coupling of the intense laser pulse with the surface and surface materials, circumventing the need for the resonant excitation employed in nanosecond laser desorption. In combination with optical spectroscopy or ion mobility detection techniques, non-resonant USPL vaporization provides an opportunity to achieve detection of low vapor pressure compounds such as explosives by desorbing intact signature from a surface, thereby making it available for gas-phase analysis. Wepropose to explore the use of non-resonant USPL vaporization as a means to increase the concentration of low-vapor pressure speciesin the gas phase above a surface to facilitate detection by coherent Raman spectroscopy (CRS) or ion mobility spectrometry (IMS). Raman spectroscopy and ion mobility spectrometry are mature technologies that have been widely used for detection and analysis of high explosives and improvised explosive devices. Raman spectroscopy has been implemented for surface analysis but detection of explosive signatures in the gas phase is compounded by the low vapor pressure of most explosive compounds, generally prohibiting its use for detection of buried or otherwise covered devices. Ion mobility spectroscopy is a mature, fielded technology that has been used widely to assist in the identification of signatures of explosives. This is a request to expand the scope of the present ONR award to perform experiments exploring the ultrashort pulsed laser desorption and ion mobility detection of explosives from water surfaces. Inaddition to DNT and TNT, the laser detection of RDX, C4 and HMX will also be investigated. This request focuses on investigations of the utility of our recently developed experiment combining the speed of hand-held ion mobility spectrometry (IMS) with ultrashort pulsed laser vaporization to detect low vapor pressure explosives signature molecules. We have recently demonstrated a million-fold enhancement in the detection limit for dinitrotoluene (DNT) and trinitrotoluene (TNT) using femtosecond laser vaporization from solid sources. In the completed measurements, the explosive molecules were deposited onto glass metal and sand substrates using drop cast and vapor spray methods. The ultrashort pulsed lasers were employed to deliver the signature molecules into the gas phase without decomposition for subsequent detection using a hand-held IMS system. Careful measurements demonstrated that the limit of detection was improved by approximately six orders of magnitude using the laser vaporization method. Our hypothesis is that the ultrashort pulsed laser interacting with the sample transfers the analyte into the gas phase much like thermal desorption is used in conventional swab-based IMS methods. The expansion of the laser vaporization method to water samples and a wider variety of explosive molecules will form the basis of the proposed research.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 24, 2023
- Source ID
- N000142312739
Entities
People
- Robert J Levis
Organizations
- Office of Naval Research
- Temple University
- United States Navy