Fastly detecting hazardous, non-volatile chemical substances on paved roads and streets is a topic of utmost military importance in an area denial scenario. Since the 1980s, inherently slow manual sampling has been avoided on armored vehicles using a small silicone wheel that continuously accumulates surface contaminations. After a given sampling period, collected (and potentially hazardous) contaminants on the wheel are thermally desorbed and analyzed by mass spectrometry. This approach led to further technological advancements, including implementing a double-wheel sampling system for automated, uninterrupted operation. Suspicious areas are examined at low driving speeds (approximating a fast-walking speed) with comparatively low spatial resolution, as the silicone wheels can only be rolled comparatively slowly to ensure continuous surface contact. Incremental improvements may further optimize the double-wheel sampling system. In that context, we are currently investigating laser desorption technology to achieve a more targeted heat treatment of the complete silicone wheel and increase spatial resolution and sensitivity. In addition, we also contribute to the development of advanced ion mobility spectrometers, which are both fast scanning and highly sensitive, as a viable alternative to cumbersome mass spectrometers. As a radically different approach, we report here on a measurement system using back-scattering IR-spectroscopy to optically interrogate samples at a standoff distance and process the information without delay. The used IR light source consists of three coupled broadband quantum cascade laser modules, each with an integrated micro-opto-electro-mechanical grating scanner (MOEMS EC-QCL). The elaborate coupling of three such pulsed laser modules provides an ultra-broadband spectral scan within the IR-fingerprint area (covered by those three MOEMS EC-QCLs) at a repetition rate of almost one kilohertz, thus resulting in measurement times of as short as one millisecond per (ultra-broadband) spectrum. We found that even minor contaminations of hazardous substances are identified using this setup. Furthermore, preliminary laboratory tests revealed a successful detection after the measurements on a fast-moving contaminated object. The experiments were performed at different observation angles with a considerable focal depth. The proof of concept shows that this novel QCL-based chemical detection approach is fast enough and promising to continuously monitor the ground with sufficient geometric resolution at cruise speeds on uneven and textured surfaces.
Volatile chemicals can form expansive toxic gas clouds after an accidental or deliberate large-scale release. The emerging toxic clouds may be invisible to the optical spectrum of the bare eye, but they are generally detectable using suitable standoff or point detectors. Standoff detectors are particularly suited for monitoring a large area within their line of sight, whereas remotely controlled point detectors may be used to survey specific areas of strategic interest. A favorable spatial and temporal detection resolution is usually achieved using standoff Fourier Transform Infrared (FTIR) spectrometers. To obtain a proper spatial resolution beyond a mere imaging view, at least two imaging systems must operate concurrently with an adequate opening angle concerning the distance of reconnaissance. During a field trial in Umeå, Sweden, we utilized an appropriate setup for standoff tomography to detect and identify comparatively small-scale chemical releases of gaseous substances and evaporating aerosols. We reached high resolutions in space and time at a standoff distance of over a kilometer. Thus, we have shown that a targeted early warning and short response times for emerging threats are possible while operators remain at a safe location. Additionally, the field trial revealed the significant influence of the properties and concentration of the deployed chemicals, wind shear, and turbulence on the detection result. In support of spatially and temporally resolved standoff detection, targeted drones carrying fast and sensitive point detectors, such as ion mobility spectrometers, may be used as an orthogonal technique to independently confirm identification.
Most reported measurement efforts for visualizing gaseous exposure signatures aim to detect and analyze continuous releases of volatile chemicals. Recently, we became particularly interested in characterizing short-time explosive releases of chemical substances. To perform such experiments, we pursued the construction of a suitable device that generates appropriate short-time events in a reproducible manner. This device, which we refer to as an aerosol bomb, allows the controlled release of liquids from 10 to 200 mL within a timeframe of one to two seconds after being pressurized up to 80 bar. Furthermore, different spray profiles and, thus, different cloud shapes can be created using customized spray nozzles. These short-time chemical exposures, however, proved challenging to visualize by video recordings as dilution and volatilization led to the rapid disappearance of visible cloud shapes. Therefore, we utilized a dual setup of passive infrared (IR) Focal Plane Arrays to detect and identify these lower concentrations of chemicals. In preceding studies, we have already shown the application of an IR focal plane array detector for hyperspectral recording and analysis of measurement fields of various sizes with 128 x 128 pixels in a time grid of two seconds. After connecting two hyperspectral imaging measurement systems into a combined dual setup, we conducted a three-dimensional (3-D) characterization of short-time chemical exposures, whereby 3-D imaging is realized by intersecting beams of IR waves.
With the purpose of validating dispersion models, ammonia (NH3) releases were performed in September 2018 and a network consisting of NH3 detectors and temperature sensors were positioned in a grid in front of the source. In addition, the test grid was also monitored by a focal plane array imaging system based on a LWIR detector, which was positioned at a safe standoff distance of 1 km. With this setup, it was possible to monitor the release and the development of the generated cloud during the dissemination, as well as monitoring surrounding areas for risk assessment purposes during and after each challenge. As the observation was performed in near real time (approximately 0.5 Hz frame rate for the measurement, data transfer, Fourier transform and analysis), it was possible to give immediate feedback to the release team and test control personnel. Of special interest are background concentrations below the detection limit, as once these are achieved this indicates whether an area is safe and/or when additional challenges/disseminations can occur.
Through the European Defence Agency, the Joint Investment Programme on CBRN protection funded the project AMURFOCAL to address detection at stand-off distances with amplified quantum cascade laser technology in the longwave infrared spectral range, where chemical agents have specific absorptions features.
An instrument was developed based on infrared backscattering spectroscopy. We realized a pulsed laser system with a fast tunability from 8 to 10 μm using an external-cavity quantum cascade laser (EC-QCL) and optical parametric amplification (OPA). The EC-QCL is tunable from 8 to 10 μm and delivers output peak powers up to 500 mW. The peak power is amplified with high gain in an orientation-patterned gallium arsenide (OP-GaAs) nonlinear crystal. We developed a pulsed fiber laser acousto-optically tunable from 1880 to 1980 nm with output peak powers up to 7 kW as pump source to realize an efficient quasi-phase matched OPA without any mechanical or thermal action onto the nonlinear crystal. Mixing the EC-QCL and the pump beams within the OP-GaAs crystal and tuning the pump wavelength enables parametric amplification of the EC-QCL from 8 to 10 μm leading to up to 120 W peak power. The output is transmitted to a target at a distance of 10 – 20 m. A receiver based on a broadband infrared detector comprises a few detector elements. A 3D data cube is registered by wavelength tuning the laser emission while recording a synchronized signal received from the target. The presentation will describe the AMURFOCAL instrument, its functional units and its principles of operation.
Within the framework of the first European Defence Agency (EDA) call for protection against chemical, biological, radiological and nuclear threats (CBRN Protection) we established a project on active multispectral reflection fingerprinting of persistent chemical agents (AMURFOCAL). A first paper on the project AMURFOCAL has been issued last year on the SPIE conference in Warsaw, Poland. This follow up paper will be accompanied by an additional paper that deals specifically with the aspect of the 100 W-level peak power laser system tunable in the LWIR. In order to close a capability gap and to achieve detection at stand-off distances our consortium built a high peak power pulsed laser system with fast tunability from 8 to 10 μm using an external-cavity quantum cascade laser and optical parametric amplification. This system had to be tested against different substances on various surfaces with different angles of inclination to evaluate the ability for an active stand-off technology with an eye-safe laser system to detect small amounts of hazardous substances and residues. The scattered light from the background surface interferes with the signal originating from the persistent chemicals. To account for this additional difficulty new software based on neutral networks was developed for evaluation. The paper describes the basic setup of the instrument and the experiments as well as some first results for this technology.
Remote detection of toxic chemicals of very low vapour pressure deposited on surfaces in form of liquid films, droplets or powder is a capability that is needed to protect operators and equipment in chemical warfare scenarios and in industrial environments. Infrared spectroscopy is a suitable means to support this requirement. Available instruments based on passive emission spectroscopy have difficulties in discriminating the infrared emission spectrum of the surface background from that of the contamination. Separation of background and contamination is eased by illuminating the surface with a spectrally tune-able light source and by analyzing the reflectivity spectrum.
The project AMURFOCAL (Active Multispectral Reflection Fingerprinting of Persistent Chemical Agents) has the research topic of stand-off detection and identification of chemical warfare agents (CWAs) with amplified quantum cascade laser technology in the long-wave infrared spectral range. The project was conducted under the Joint Investment Programme (JIP) on CBRN protection funded through the European Defence Agency (EDA).
The AMURFOCAL instrument comprises a spectrally narrow tune-able light source with a broadband infrared detector and chemometric data analysis software. The light source combines an external cavity quantum cascade laser (EC-QCL) with an optical parametric amplifier (OPA) to boost the peak output power of a short laser pulse tune-able over the infrared fingerprint region. The laser beam is focused onto a target at a distance between 10 and 20 m. A 3D data cube is registered by tuning the wavelength of the laser emission while recording the received signal scattered off the target using a multi-element infrared detector. A particular chemical is identified through the extraction of its characteristic spectral fingerprint out of the measured data.
The paper describes the AMURFOCAL instrument, its functional units, and its principles of operation.
The mobile demonstrator for biological aerosol standoff detection has been designed and built to test and develop
reliable optical methods for the identification of biological aerosols in a 10 km range. Disciplines such as agriculture,
defense and security are increasingly concerned with distinguishing certain classes of biological particles from remote
distances. The instrument combines backscatter channels for 3 laser wavelengths, 2 nitrogen Raman channels,
depolarization and fluorescence channels with 2 ultraviolet excitation wavelengths. Aerosol size distribution, particle
shape and refractive index as well as fluorescence excitability by different laser wavelengths and spectral fluorescence
information are the distinguishing variables for the identification of unknown biological aerosols.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.