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Solid State UV Raman Trace Explosive Detector

Description:

TECHNOLOGY AREA(S): Electronics 

OBJECTIVE: To develop an ultraviolet (UV) Raman standoff spectroscopic system with an excitation wavelength below 250 nm, and recommended > 230nm. The system shall utilize solid-state laser technology for the excitation source and shall be capable of detecting trace explosive particulates on surfaces at standoff distances of greater than 1 meter with a time-to-detect of a few seconds. 

DESCRIPTION: Fielded CBRNE detection capabilities rely on direct contact with or entrapment of the solid sample or the associated trace explosives above the contaminated surface with the sensor. An ideal detector is Unmanned Ground Vehicle (UGV)-compatible with the ability to rapidly scan over surfaces from a few meters away and precisely identify a combination of chemical, biological, and explosives threats, thereby warning personnel who can remain at a safe distance. Such a sensor does not currently exist. Raman spectroscopy is an attractive detection technique because it requires no sample preparation, and gives a high degree of chemical specificity. The use of ultraviolet (UV) excitation provides improved sensitivity over visible or near IR excitation because of the larger cross-sections, along with possible enhancement of the signal intensity if the excitation wavelength is near that of an electronic transition (resonance or pre-resonance Raman). In addition, for excitation wavelengths shorter than 250 nm the fluorescence emission is separated spectrally from the Raman scattered light [1,2]. UV Raman systems have been built to detect and identify bulk, and in some cases, trace level explosive contamination on surfaces at ranges of 10 to over 100 meters sensitivities decreasing with increasing range to the target [3,4]. While showing promise for standoff explosives detection, these systems tend to be large and require high UV laser power. While excimer lasers can provide the requisite power, they require cylinders of toxic gas mixtures, tend to be large and heavy, and do not have the reliability associated with diode-pumped solid-state lasers. The goal of this effort is to design, fabricate and test a UV Raman sensor for the detection and identification of trace explosive residue at ranges of at least 1 meter, based on a solid-state laser excitation source, and compatible with point-scanning from a UGV platform. The system requirements are: Excitation Wavelength: 230 to 250 nm; Laser Source: Solid State diode-pumped laser; Spectral Resolution and Coverage: An average of 15 - 25 cm-1 between 300 – 2200 cm-1; Sensitivity: Detection and identification of explosives residues at an areal density of 1 µg/cm2 and particles between 5 and 10 micron in size; Standoff Distance: at least 1 m; Total Sensor Size (including any necessary thermal management capability for operation between -25 and 120 degrees F): < 4 cu. ft; Total Sensor Weight: < 90 lbs; Time To Detect < 5 sec. 

PHASE I: Phase I shall develop a conceptual design for the sensor and demonstrate the technical feasibility of the proposed design. Technical feasibility shall be demonstrated through modeling confirmed by UV Raman measurements made with the objective laser with the required excitation wavelength and required power. Modeling results shall include the maximum achievable scan rates (interrogation area/integration time) enabling detection and identification for the specified surface density. Demonstration of technical feasibility in Phase I is required for a Phase II contract. 

PHASE II: Construct, test, and deliver a UV Raman sensor meeting the provided specifications. 

PHASE III: In addition to use for the Department of Defense (DoD) explosive detection, the system has commercialization activity for Chemical or Biological detection and civilian uses for first responders and law enforcement. DoD uses could include sensitive site exploitation, explosives detection, treaty verification and technology upgrades to the Chemical Surface Detector Program. Civilian uses could include identification of illicit drugs, inspection of food and/or hazardous waste containers. 

REFERENCES: 

1: Erik D. Emmons, Ashish Tripathi, Jason A. Guicheteau, Augustus W. Fountain, III, and Steven D. Christesen, "Ultraviolet Resonance Raman Spectroscopy of Explosives in Solution and the Solid State," J. Phys. Chem. A 117, 4158-4166 (2013).

2:  Steven D. Christesen, Jay Pendell Jones, Joseph M. Lochner, and Aaron M. Hyre, "Ultraviolet Raman Spectra and Cross-Sections of G-series Nerve Agents," Appl. Spectrosc. 62(10) 1078-1083 (2008).

3:  L.C. Pacheco-Londono, W. Ortiz-Rivera, O.M. Primera-Pedrozo, S.P. Hernandez-Rivera. ‘‘Vibrational Spectroscopy Standoff Detection of Explosives’’. Anal. Bioanal. Chem. 395(2), 323-335 (2009)

4:  Augustus W. Fountain III, Steven D. Christesen, Raphael P. Moon, Jason A. Guicheteau, and Erik, D. Emmons, "Recent Advances and Remaining Challenges for the Spectroscopic Detection of Explosive Threats," Appl. Spectrosc. 68(8) 795-811 (2014).

KEYWORDS: Raman, Solid State UV Lasers, Explosives, Detection 

CONTACT(S): 

Raphael Moon 

(410) 436-6624 

raphael.p.moon.civ@mail.mil 

John Strawbridge 

(410) 417-3518 

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