US Government As Represented by the Secretary of the Army

Rosario C Sausa

Josef B Simeonsson

Jerry B Cabalo

Robert Pastel

Josef Simeonsson

Richard B Murray

George W Lemire

Robert L Pastel

George Lemire

Robert J Lieb

Embodiments of present invention are directed to near infrared (IR) laser-induced vibrational absorption systems and methods for material detection. According to one embodiment, a system for detecting materials may include: at least one laser configured to output light in the near IR spectrum so as to excite at least one vibrational overtone frequency, at least one combination band frequency, or a combination thereof, of a sample comprised of one or more of materials; a detector configured to detect a physical phenomenon of the sample in response to laser excitation; and an analyzer configured to the analyze the detected physical phenomenon and to identify the one or more materials based comparison of the detected signatures with known signatures of one more materials.

Near-IR laser-induced vibrational overtone absorption systems and methods for material detection

A laser-based photoacoustic sensor performs trace detection and differentiation of atmospheric NO and NO.sub.2 in order to obtain respective concentrations for NO and NO.sub.2 using photoacoustic spectroscopy. The device of the invention employs a single, pulsed laser having two outputs near 454 nm and 227 nm, respectively, to irradiate a sample vapor, the sample vapor being collected by a hand-held wand. A photoacoustic response from both NO and NO.sub.2 is detected using microphone detectors, is converted into electrical signals, and is analyzed using a microcomputer. The results of the analysis--the respective concentrations of NO and NO.sub.2 in the sample vapor--are displayed on a digital oscilloscope. Preferably, the electrical signals are amplified prior to analysis, and a boxcar integrator is used to sample and average the electrical signals during the analysis operation.

Laser-based photoacoustic sensor and method for trace detection and

The excitation of the target nitrocompound with ultraviolet radiation ress in photodissociation yielding vibrationally excited NO with significant population of the v'=1 and v'=2 levels of the ground electronic state. As the population distribution of ambient NO favors the v'=0 level, discrimination between vibrationally excited NO and ambient NO is possible by probing the NO A-X (0,0),(1,1), and (2,2) bands near 226, 224, and 222 nm, respectively, employing (1+1) resonance-enhanced multiphoton ionization (REMPI). Many complex nitrocompounds cannot be photolyzed near 452 nm since their absorption cross sections are relatively small. Thus, the visible laser radiation is used to facilitate the detection of ambient NO and NO from NO.sub.2 by (2+2) REMPI and to discriminate these species from more complex nitrocompound analytes. The analytical utility of the present invention has been demonstrated at several photolysis/ionization wavelengths for NO/CH.sub.3 NO.sub.2 and NO.sub.2 /CH.sub.3 NO.sub.2 mixtures. Limits of detection have also been determined for NO, NO.sub.2, nitromethane (CH.sub.3 NO.sub.2), nitrobenzene (C.sub.6 H.sub.5 NO.sub.2) diethylglycoldinitramine (DEDGN), and trinitrotoluene (TNT), and are in the ppb to ppm range.

Device and process for detecting and discriminating NO and NO.sub.2 from

A method and apparatus is provided for real-time detection of trace amounts of atmospheric and tropospheric halogen-containing compounds. The present invention can be used either for in situ detection or remote sensing. A laser is employed to induce photofragmentation of the halogenated molecules and facilitate detection of the characteristic atom fragment by stimulated emission spectrometry. For brominated compounds, the output of a single laser is tuned to the strong two-photon 4p.sup.4 5p .sup.4 D.degree..sub.3/2 .rarw.4p.sup.5 2 P.degree..sub.3/2 transition of Br at 260.634 nm. The Br atoms are subsequently detected by stimulated emission (SE) via the 4p.sup.4 5p .sup.4 D.degree..sub.3/2 .fwdarw.4p.sup.4 5s .sup.4 P.sub.5/2 transition at 844 nm. For comparison, the laser-induced fluorescence (LIF) signal at the same wavelength is also monitored. The SE signal is distinct from the fluorescence in that it is coherent, bidirectional, and propagates coaxially with the laser beam. As a result of photophysical amplification, it is approximately two orders of magnitude greater than the LIF signal. The present invention has been demonstrated for trace detection of CHBr.sub.3 and CHClBr.sub.2 in N.sub.2 or air at total gas pressures of 1-760 Torr. Detection limits are in the parts-per-million range. The absorption cross section of the two-photon 4p.sup.4 5p .sup.4 D.degree..sub.3/2 .rarw.4p.sup.5 2 P.degree..sub.3/2 transition is estimated to be 3.8.times.10.sup.-43 cm.sup.4.

Detector of halogenated compounds based on laser

A hand-held probe monitors the presence of trace hazardous materials including nitrocompounds and halogen-containing compounds. The hand-held probe provides real-time and in-situ site characterization and analysis. The probe operates in accordance with a laser photofragmentation/fragment detection technique which employs one or more lasers for photolysis of the analyte molecules and/or facilitating the detection of the characteristic fragments by multiphoton ionization. The probe includes a tunable laser, a pair of miniature electrodes coupled with a fiberoptic cable and lens assembly mounted in a sweep wand, and a data and analysis system. An adjustable laser beam stopper allows for atmospheric sampling or surface analysis at the point of interest. Applications include the detection of nitrocompounds by probing the characteristic NO photofragment and halogenated compounds by probing the respective characteristic halogen atom photofragment. The monitoring of other hazardous materials and pollutants is possible.

Hand-held probe for real-time analysis of trace pollutants in atmosphere

A subsurface soil contaminant identification system employs a cone penetrometer unit for continuously measuring the concentration of energetic materials in potentially contaminated soils. The sensor is rugged, reliable, and has a fast response time. The invention utilizes two pulsed, time-delayed miniature lasers. An infrared laser is used for decomposing the energetic material into NO and other products, while a visible laser operating near 452 nm is used for NO detection by (2+2) resonance-enhanced multiphoton ionization (REMPI). The system employs a fiber optic to transmit the output radiation at distances of approximately 30-50 meters, a lens assembly to focus one or both laser beams, a pair of miniature electrodes to collect the ions, a penetrometer, and data acquisition/processing equipment. A REMPI spectrum of 0.1% NO at atmospheric pressure reveals that the spectral resolution is sufficient such that characteristic spectral features of NO can be identified unequivocally.

Sensor and method for detecting trace underground energetic materials

A method for the ultra-sensitive detection of atmospheric and surface adsorbed nitrocompounds such as propellants, explosives, and nitro-pollutants employs an excimer (ArF) laser operating at or near 193 nm to photofragment the target molecule and facilitate the detection of the characteristic NO fragment, formed from the dissociation of NO.sub.2, by resonance-enhanced multiphoton ionization (REMPI) and/or laser induced fluorescence (LIF) via its A-X, B-X, C-X, and/or D-X electronic transitions. In addition to NO, the detection of other fragments, such as C, CH, C.sub.2, NH and OH, by their ionization and/or prompt emission resulting from 193 nm excitation enhances the analyte identification. The analytical utility of this apparatus and method has been demonstrated on a number of compounds including dimethylnitramine (DMNA), nitromethane, nitrobenzene, orthonitrotoluene, para-nitrotoluene and trinitrotoluene (TNT). With the present system, limits of detection in the tens to hundreds of parts-per-billion (ppb) range have been achieved in the gas phase for all of these compounds, using only 1 mJ of laser energy at 193 nm.

Method for detecting nitrocompounds using excimer laser radiation

An apparatus and method for the sensitive detection of atmospheric and/or surface absorbed nitrocompounds has been developed. The apparatus and method may be employed to detect the presence or absence of propellants, explosives, and nitropollutants. The unique feature herein is that the apparatus and method employ one laser operating at or near 226 nm. The laser photofragments the target molecule and facilitates the detection of the characteristic NO fragment, by resonance-enhanced multiphoton ionization (REMPI) and/or laser-induced-fluorescence (LIF) via its A.sup.2 .SIGMA..sup.+ -X.sup.2 II.sub.i transitions. The analytical utility of this apparatus and method has been demonstrated on numerous compounds, such as, DMNA, nitromethane, nitro-benzene, TNT, and RDX. With the present system, a limit of detection of 8 and 24 ppb is obtained for RDX and TNT, respectively, using only 100 micro-Joules per pulse of laser energy. Limits in the sub parts-per-trillion are projected using higher laser energies and improved system design.

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Bel Air, MD, United States of America

Rosario C Sausa