WO2018213212A1 - Détection chimique à l'état de trace à distance par spectroscopie infrarouge active - Google Patents

Détection chimique à l'état de trace à distance par spectroscopie infrarouge active Download PDF

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WO2018213212A1
WO2018213212A1 PCT/US2018/032623 US2018032623W WO2018213212A1 WO 2018213212 A1 WO2018213212 A1 WO 2018213212A1 US 2018032623 W US2018032623 W US 2018032623W WO 2018213212 A1 WO2018213212 A1 WO 2018213212A1
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target
source
detector
stand
pulse beam
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PCT/US2018/032623
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English (en)
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Augie IFARRAGUERRI
Brian Gorin
J. Frank CAMACHO
Noah Christian
Robert Rice
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Leidos, Inc.
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/28—Investigating the spectrum
    • G01J3/45—Interferometric spectrometry
    • G01J3/453—Interferometric spectrometry by correlation of the amplitudes
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N2021/1793—Remote sensing
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
    • G01N2021/3595—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using FTIR
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2201/00—Features of devices classified in G01N21/00
    • G01N2201/10—Scanning

Definitions

  • applications requiring or benefitting from chemical detection include, for example: screening of people, vehicles, cargo as they attempt to cross borders, enter checkpoints and enter public or other high traffic facilities including airports, train stations, sports and/or concert venues, office buildings, shopping centers and the like; detection of residue or pre-cursor or constituent materials from explosives, poisons, narcotics or other hazardous materials; tracking people and things through surveillance.
  • Laboratory analysis techniques such as Nuclear Magnetic Resonance spectroscopy (NMR), mass spectrometry, Fourier Transform Infrared (FTIR) spectroscopy, and various forms of chromatography provide precise chemical identification from very small quantities of sample material. But there is a time lag of hours to days for a sample to be collected and transported to the laboratory and collecting enough samples to comprehensively analyze large areas for trace surface residues is cost and time prohibitive.
  • Field-portable versions of several of these techniques do exist, which reduce analysis time to minutes, but to test for surface residue samples must still be collected by wiping or swabbing the surface(s) of interest. Also, the sensitivity and specificity of field-portable instruments is significantly lower than the
  • Optical spectroscopy based standoff techniques are the most viable approach for rapid, high area coverage chemical detection of trace residues on surfaces. But while a number of existing standoff optical spectroscopy techniques such as fluorescence spectroscopy, differential absorption light detection and ranging (DIAL), Raman spectroscopy, and laser induced breakdown spectroscopy (LIBS) offer either high sensitivity or high specificity, none can simultaneously provide the needed performance metrics in both categories. Many optical standoff techniques also have additional drawbacks, such as eye safety concerns.
  • narrow-band coherent sources that limit spectral coverage and therefore sensitivity.
  • dispersive spectrometer-based detection used with many current passive and actively illuminated systems, intrinsically trades signal-to-noise (S R), resolution, and scan speed, because the collected photons must be dispersed and separated into individual resolution elements prior to detection.
  • S R signal-to-noise
  • scan speed because the collected photons must be dispersed and separated into individual resolution elements prior to detection.
  • open-path FTIR relies on efficient retro-reflectors that preserve the transmitted energy and use large collimating optics to project the thermal energy of the infrared source. Even with these advantages, large apertures are still required.
  • Tunable lasers that scan the spectrum over time, dense frequency combs that generate a multitude of narrow lines, and super-continuum (SC) lasers that produce spectrally continuous output.
  • Tunable laser sources in the mid-IR have been around for many years.
  • Frequency-agile CO2 lasers use gratings to switch among the multitude of lines generated by the source.
  • QCLs represent the new generation in mid-IR laser sources. They offer better efficiency than CO2 and broad tunability. QCLs can be made to cover all parts of the mid- IR and beyond.
  • a tunable laser-based system scans the spectrum by quickly switching wavelengths over its "tuning range," so a sensor that relies on it would be very simple, only requiring a broadband detector because the spectroscopy is built into the source.
  • tunable source-based systems by only illuminating one line at a time, the overall efficiency is very low compared with a source that can illuminate many wavelengths at once.
  • Dense frequency combs can be generated with QCLs. Assuming that the power per line is the same as with a tunable source, combs have an efficiency advantage of a factor equal to the number of lines over the tunable source, at the expense of complexity in the receiver, which must now perform the spectroscopic function (or by modulating the source— either way, complexity is unavoidable). However, they are still discrete by nature and therefore only provide information on the spectral lines for which they are designed. Unlike frequency combs, SC sources are continuous and thus their output energy interacts with all of the absorption lines from the materials it encounters.
  • SC sources have been the requirement for pulsed lasers, unlike CO2 or QCL lasers, which are continuous-wave, but with the availability of fast detectors and electronics, the present embodiments capture the individual pulses and reject the background energy while reducing the detector noise via shorter integration times.
  • a preferred system would feature portability and real-time results with high chemical sensitivity and specificity across a broad range of target classes and effective operation in a real- world environment accounting for issues such as gas phase and surface-adsorbed clutter, varying substrates, temperature, humidity, indoor/outdoor background light.
  • the present embodiments aim to overcome these limitations by coupling broadband coherent sources with interferometric spectroscopy.
  • This completely new type of sensor combines the functionality of an open-path FTIR spectrometer with that of a surface chemical probe.
  • the system consists of a pulsed supercontinuum (SC) laser source, a high-speed compact FTIR spectrometer, optical transmitter, telescope, high-speed infrared detector and a computer processor.
  • the supercontinuum laser light is scanned over the field of view.
  • the covering SC laser covers the 2-12-micron spectral range.
  • the high-speed FTIR spectrometer is synchronized to the source so that the pulses are captured, and the spectrum measurements coincide with the individual scan positions of the source. A small portion of the transmitted energy from the source is tapped and directed to the
  • the computer processor converts the raw data to target and reference spectra.
  • a stand-off chemical detector for detecting one or more materials on a target, the detector includes: a pulsed supercontinuum (SC) laser source operating in the infrared spectrum for generating a source pulse beam for target illumination; an interferometric device for spectrally modulating the source pulse beam; an optical transmitter for directing the spectrally modulated source pulse beam to the target and sampling the source pulse beam to obtain a source reference measurement signal; an optical receiver for collecting a reflected source pulse beam from the target and the source reference measurement signal from the optical transmitter; at least one infrared detector for detecting the target reflected source pulse beam and the source reference measurement signal as a series of interferograms; a digitizer for digitizing the interferograms; and a processor for producing spectrograms from the digitized interferograms, wherein the spectrograms are indicative of one or more materials on the target.
  • SC pulsed supercontinuum
  • interferometric device for spectrally modulating the source pulse beam prior to interaction with the target; and a detector for receiving a reflected source pulse beam, wherein the reflected source pulse beam includes spectral information for detecting one or more materials on the target.
  • a process for scanning a target located at a distance of at least 3 meters from a stand-off detector to detect one or more materials thereon includes: scanning the target with a source pulse beam emitting in a spectral range of approximately 2 to 12 ⁇ generated by a supercontinuum (SC) laser source, wherein prior to reaching the target, the source pulse beam is spectrally modulated by a refraction-based interferometric modulator and sampled by an optical component to obtain a source reference measurement signal; receiving at an optical receiver a reflected source pulse beam from the target and the source reference measurement signal from the optical component; detecting by at least one infrared detector the target reflected source pulse beam from the target and the source reference measurement signal source reference measurement signal as a series of interferograms; digitizing the interferograms by a digitizer; and processing the interferograms to produce spectrograms to detect the inclusion of one or more materials on the target.
  • SC supercontinuum
  • Figure 1 is an exemplary schematic of components and functions of an embodied system
  • Figure 2 provides an exemplary power spectrum of the SC laser source
  • Figure 3 shows the signaling timing diagram for the preferred embodiment
  • Figure 2 illustrates the signal processing chain used to calculate the spectrum from the raw interferogram data
  • Figure 5 illustrates the spectral match between a measured sample of pentaerythritol tetranitrate (PETN) and a reference measurement collected with a conventional laboratory instrument;
  • PETN pentaerythritol tetranitrate
  • Figure 6 shows the exemplary spectral S R achieved by the preferred embodiment standoff system
  • Figure 7 shows the measured spectrum of polystyrene by the system of the preferred embodiment, compared to the standard transmission spectrum from NIST.
  • the embodied system is directed to a standoff chemical analyzer capable of detecting and identifying trace amounts of solids, liquids, and vapors from distances in the 10s of meters.
  • a standoff chemical analyzer capable of detecting and identifying trace amounts of solids, liquids, and vapors from distances in the 10s of meters.
  • Such a sensor is highly significant in that it provides the ability to probe surfaces for contamination unobtrusively from a safe distance, scan people and vehicles for illicit substances, and monitor effluents from buildings without the need for a retro-reflector or line of sight to the sky.
  • the system scans a 1 m x 1 m target area at a distance of 3-30 m. Scanning is performed by the coherent transmit beam aimed with the help of a thermal camera, while the receiver subtends the full target area being scanned, which is possible because the pulsed signal is detected via changes relative to the thermal background so that the ambient background radiance is invisible to the sensor. Dividing the target area into subsections directly improves our signal-to-clutter performance by increasing the proportion of the signal originating from the target (e.g., surface contaminant) relative to background materials where the material of interest only covers a small area (square centimeters) or is not uniformly distributed.
  • the target e.g., surface contaminant
  • the target is scanned in any number of grid configurations up to 30 x 30 over a 15-second measurement period, as a single field of view for maximum sensitivity, or even adaptively to implement a detect-and-confirm strategy if desired.
  • the active source is a supercontinuum (SC) laser.
  • the SC laser may include adjustable beam divergence.
  • the transmitted light is modulated by a high-speed Fourier-transform spectrometer chosen for its compatibility with the proposed system described below.
  • Figure 1 General components of an exemplary embodiment are depicted in Figure 1 which comprises several major electro-optical sub-systems: supercontinuum ("SC") fiber laser source 10; FTIR interferometer 15; optical transmitter 20, including transmit optics and scanner; optical receiver 25, e.g., receive telescope; IR detector 30; signal digitizer 35; processor 40; and user interface 45 and controller 50 for control and display.
  • SC supercontinuum
  • the mechanical design and materials are selected to mitigate stray light, enable thermal management, and be light-weight.
  • a SC laser source delivers broad-spectrum light to the surface of interest.
  • Figure 2 provides an exemplary output spectrum from a source that has been used for this purpose.
  • SC lasers combine the spatial coherence properties of lasers with broad spectral emission and high brightness.
  • the SC laser beam can be collimated with relatively small optics and projected on a distant target with low divergence.
  • the propagation of the SC source is limited by the atmosphere (turbulence, scattering, and absorption).
  • Omni Sciences has developed a mid-infrared SC laser (MISCL) with a 5.2-W output that spans the 2-4.3 ⁇ wavelength range.
  • the Omni Sciences fiber laser architecture is a platform where SC in the visible, near-infrared, or mid-infrared can be generated by appropriate selection of the amplifier technology and the SC generation fiber.
  • SC in the visible, near-infrared, or mid-infrared can be generated by appropriate selection of the amplifier technology and the SC generation fiber.
  • the output of the SC source is optically collimated and run through the
  • interferometric device for modulation at varied optical path differences (OPDs).
  • OPDs optical path differences
  • the three primary methods for performing spectroscopy are dispersive (using gratings or prisms), interferometric, or tunable filters.
  • Interferometric methods for spectral measurement have many classical advantages over dispersive and tunable filter instruments. These advantages include Jacquinot's advantage, or throughput advantage, because of the lack of any entrance slit; and Fellgett's advantage, or the multiplex advantage, which is a result of all resolution elements being observed all the time.
  • FTIR uses an interferometer (typically a Michelson, Mach-Zehnder, or Sagnac configuration), where two optically varied path lengths are used to collect the individual points of the interferometric series.
  • This series of intensities with varied path-length differences is collected at a detector as an interferogram.
  • the interferogram is Fourier- transformed to obtain the spectrum of light entering the interferometer.
  • the mirror placement is performed using a linear motor on a mirror to obtain the varied mirror retardations, i.e., reflective scanning, but in the preferred embodiment discussed herein, the interferometry is enabled by a configuration that utilizes refractive scanning through an innovative rotational displacement of a refractive optical element as described in U.S. Patent Nos. 4,654,530 and 5, 173,744, which are incorporated herein by reference in their entirety. This rotation can be accomplished at high speed, and the interferometer has significant advantages in speed, size, weight, and power over traditional moving-mirror interferometers.
  • a mathematical model that predicts the OPD for a given refractor angle is available.
  • this model predicts a non-linear relationship between the OPD and rotor angle.
  • the SC laser source produces pulses at a constant frequency, which translates to constant angular sampling for a given refractor rotation rate, and therefore the OPD sampling is non-linear.
  • An internal CW reference laser e.g., diode laser, of well-known wavelength provides a signal that is measured concurrently with the pulses to provide information on the actual OPD at the time of each pulse. The theoretical basis for this approach is discussed in Attachment A of U.S. Provisional Patent Application No. 62/506,218 which is incorporated herein by reference and to which the present application claims the benefit of priority.
  • moving-mirror or moving-refractor FTIR instruments include the use of fixed interferometers (Fabry -Perot or Sagnac), selective or multiple etalons (Fabry -Perot and variants), and holographic instrumentation (virtually imaged phase array [VIPAJor VIPA etalons). These may be used in alternative embodiments, but the TurboFT or equivalent refractive scanning instrument is preferred, even with the integration risk of a pulsed laser source, because it provides significant advantages over these other approaches.
  • Fixed interferometers Fabry -Perot or Sagnac
  • Fabry -Perot and variants selective or multiple etalons
  • holographic instrumentation virtual imaged phase array [VIPAJor VIPA etalons
  • interferometers are sufficient when a narrow spectral range needs to be identified, but are not useful for collection of full spectra from 2-12 ⁇ .
  • Grating spectrometers do not have the throughput, wavelength, and multiplex advantages that an FTIR has, and even a dispersive arrayed instrument requires an incoming slit that limits throughput.
  • the dispersive arrayed system does not have the equivalent resolving power and resolution that the FTIR has, and the resolving power is not linear over the wavelength range.
  • Holographic (e.g., VIPA) arrays offer an intriguing approach to solving some of the dispersive instrumentation issues by not requiring an entrance slit and thus permitting a theoretically comparable throughput advantage to FTIR instrumentation.
  • very high resolutions down to tens of GHz
  • they are currently limited in terms of total spectral range, much like Fabry -Perot instruments, when compared with FTIR.
  • the modulated light from the interferometer is guided by the optical transmitter to the target some distance away (typically 3-30 meters).
  • the target some distance away (typically 3-30 meters).
  • a small fraction of the light from the interferometer is sampled and directed to the detector, arriving earlier than the delayed pulse from the target. This signal allows for the proper correction of the measured target spectrum.
  • the optical receiver gathers light returning from the target and directs it to the detector.
  • the low-speed detector assembly of the TurboFT product may be replaced with a high-bandwidth detector to obtain fast temporal response while maintaining detectivity.
  • the preferred detector is a high-speed photoconductive
  • MCT mercury/cadmium telluride
  • the signal from the detector is digitized, resulting in a pulse pair (one reference pulse and one target pulse) for each OPD.
  • the delay between the reference and reflected pulses indicates the distance to the target.
  • data acquisition is achieved using a two-channel digitizer (e.g., U5303A digitizer from Acqiris (formerly Keysight)) that is able to capture up to 2 GS/s per channel with 12-bit depth.
  • U5303A digitizer from Acqiris (formerly Keysight)
  • one channel is used for the detector signal while the other is used to capture the signal from the
  • the channels are synchronized by a common clock, which allows us to match the source pulse times with reference diode for calculating the Fourier transform.
  • the 12-bit quantization provided by the digitizer is sufficient assuming that the signal range is near-optimally matched to the digitizer. As the target reflectance increases from the derivation point, the digitizer quickly saturates.
  • the preferred embodiment implements a dynamic gain adjustment strategy that relies on multiple scans for each target location. If saturation is detected in the first scan, it is discarded, and the gain is lowered to prevent saturation in the following scan. This procedure is repeated until no saturation is detected.
  • a signaling scheme may be used whereby the source produces a trigger signal each time a pulse is generated. This signal serves to trigger data acquisition, which then takes place over a fixed number of samples.
  • the digitizer is programmed to collect a fixed number of samples at the maximum acquisition rate so that the short pulses can be captured. The number of samples must be sufficiently large to capture both the reference and target (return) pulses, which are separated in time by anywhere from 20 to 300 nanoseconds depending on the distance from the sensor to the target. For example, in a preliminary configuration, 400 samples (200 nanoseconds) are collected to ensure that (1) both the reference and target pulses were captured and (2) there are enough data points from the internal reference diode to reconstruct the full signal in spite of gaps.
  • Each sample collected to create an interferogram consists of a single pulse.
  • the total energy of the pulse (the area under the curve) gives the desired value of the interferogram point.
  • a collection of pulses is processed to estimate their total energy, thus creating the interferogram.
  • a Fourier transform (FT) is applied to each interferogram to obtain the "raw" spectra for the reference and target signals. Using the pair of spectra along with the calibration procedure described below, the apparent reflectance of the target material (including any contaminants) is estimated.
  • the sensor uses a relatively simple signaling scheme to synchronize the pulsed laser source and data acquisition.
  • the source operates at a constant pulse rate but can be externally modulated.
  • Figure 3 shows the timing diagram for the preferred embodiment.
  • the main driving signal is a 1/revolution encoder pulse from the TurboFT spectrometer motor, which in turn produces a custom on/off modulation signal for the source through an arbitrary function generator.
  • the arbitrary function generator is programmed with the appropriate timing information, which is tied to the rotation rate.
  • the source is enabled by the rising edge of each modulation signal and turned off by the falling edge.
  • Figure 4 shows the overall processing pipeline starting with the acquisition of a set of records (sample sequences containing pulse pairs) corresponding to 1 modulation cycle of the source, which is typically set for at least 6000 pulses.
  • the reference and target pulses are segmented using a fixed time delay (the algorithm assumes that the target is always far enough that the pulses do not overlap).
  • the pulse energy is estimated by numerical integration.
  • the result is a pair of interferograms.
  • the signal from the reference 850nm internal diode laser is captured for use in estimating OPD at the exact time of arrival of each pulse by the processing described below.
  • v is the wavenumber in cm "1 and a is the refractor angle associated with each interferogram sample.
  • OPD(a,n(v)) has units of centimeters and is calculated in accordance with the discussion below.
  • the parameter n(v) is the wavenumber-dependent index of refraction of the refractor.
  • the captured reference 850 nm diode laser data provides the information to determine the center time stamp for each fringe and identify the "central fringe" where the OPD is zero. Each fringe away from zero (in both positive and negative directions) corresponds to an OPD change equal to the wavelength of the reference laser. If we assume that the refractor is rotating at a constant angular rate, then we can derive an empirical curve of OPD vs. angle for the diode. We compare this curve to one predicted from the mathematical model to adjust the nominal rotation rate (which may vary by a few percent over time) so that the model and data match optimally (in the least squares sense).
  • the preferred embodiment may incorporate low-power embedded processors.
  • the pulse energy estimation may be implemented on a field-programmable gate array (FPGA) connected directly to the digitizer circuit.
  • FPGA field-programmable gate array
  • the FPGA can be equipped with dynamic memory to hold the pre-computed pulse shapes, which could be externally updated by the main processor at regular intervals if needed. That leaves the centroid and regression floating point calculations to be implemented.
  • FPGA implementation may also be used to find the timestamps for the reference diode laser fringes.
  • the required operations involved are simple and repetitive (finding zero- crossings, counting cycles, and linearly interpolating).
  • An exception to FPGA processing is finding the central fringe, which requires a complex polynomial fit, better suited to a central processor.
  • the spectrum calculation may be implemented on a graphics processing unit (GPU), where the matrix elements can be computed in parallel.
  • GPU graphics processing unit
  • S R v) S T (v) Q t(v) 2 r(v)
  • v is the wavenumber in cm "1
  • SR(V) represents the spectral power density at the receiver aperture
  • Si(p) is the transmitted spectral power density.
  • ⁇ is the fraction of the hemisphere subtended by the receiver aperture, which is known by measuring the distance from the sensor to the target.
  • the variables r(v) and t(v) represent the reflectance of the target (as modified by any contaminant) and the transmittance of any intervening atmosphere, including the effects of vapors of interest.
  • the preferred embodiment implements a dynamic gain adjustment strategy that relies on multiple scans for each target location. If saturation is detected in the first scan, it is discarded, and the gain is lowered to prevent saturation in the following scan. This procedure is repeated until no saturation is detected.
  • the raw target spectrum Si(p) is divided by another spectrum SSM(V) that is calculated from the reference spectrum SR(V) via the equation:
  • the standard material is a diffuse gold-coated target such as
  • InfraGard ® which has high reflectivity at all bands. From this data, consisting of raw spectrum pairs obtained as described above, we estimate C p, ⁇ ) using the Partial Least Squares method known to those familiar with the art. We find that in practice, 10 measurements over a period of an hour are adequate to capture the variability in the source and the atmosphere.
  • the estimated reflectance of the target provides the chemical information needed to perform material identification. This can be done via an appropriate spectral matching algorithm such as Adaptive Coherence Estimation (ACE), Spectral Feature Fitting, or Probabilistic
  • FIG. 5 provides an illustration of a spectral match between a measured sample of pentaerythritol tetranitrate (PETN) and a reference measurement collected with a conventional laboratory instrument. It can be clearly seen that the spectral features overlap, demonstrating the ability of our invention to detect and identify infrared-active materials.
  • PETN pentaerythritol tetranitrate
  • the critical performance metrics for the standoff system are the signal-to-noise ratio (SNR) and spectral frequency calibration accuracy.
  • SNR signal-to-noise ratio
  • the sensor spectral resolution is fixed, and the spectral coverage is limited by either the source spectrum or the detector spectral response.
  • the SNR measures how well the testbed system is able to capture and maintain the optical signal.
  • the pulse SNR is the ratio of the maximum pulse voltage to the root-mean-square (RMS) noise voltage seen by the acquisition system when no pulses are transmitted.
  • the final pulse SNR was 26 dB.
  • the pulse SNR is a coarse metric that provides little insight into the spectral performance.
  • spectral SNR which is the ratio of the reference spectrum to the out-of-band noise standard deviation.
  • the spectral SNR achieved by the preferred embodiment standoff system is provided in Figure 6.
  • the SNR is limited by the source power spectrum. At high frequencies, the limitation is due to the detector responsivity.
  • the spectral (frequency) accuracy of an FTIR depends on accurate knowledge of the OPD at each sample.
  • the modified TurboFT we use the internal reference laser signal to extract the OPD information to a high degree of accuracy, plus we account for the spectral variation in the refractive index in order to obtain the correct spectral scale.
  • Figure 7 shows the measured spectrum of polystyrene by our system, compared to the standard transmission spectrum from NIST. The strong overlap of the spectral features indicates that our FT matrix calculation provides correct results. Note that we are able to at least partially reconstruct spectral features that fall within the atmospheric absorption windows. This is a promising and unexpected result.
  • the system and process described herein may be used to detect numerous materials from a standoff position, including but not limited to: explosives such as Nitro-based compounds PETN and RDX, newer formulations such as acetone peroxide, and home-made explosives such as fertilizer bombs; chemical weapons and poisonous or toxic chemicals such as Sarin or Tabun, newer non-traditional agents, and toxic chemicals that may be intentionally or unintentionally released such as hydrogen cyanide or ammonia gas; Narcotics such as illicit drugs cocaine, heroin, or methamphetamine, or legal but abused drugs such as Vicodin or hydrocodone; and secondary targets including compounds associated with the manufacture and deployment of biological agents and nuclear materials.
  • explosives such as Nitro-based compounds PETN and RDX, newer formulations such as acetone peroxide, and home-made explosives such as fertilizer bombs
  • chemical weapons and poisonous or toxic chemicals such as Sarin or Tabun, newer non-traditional agents, and toxic chemicals that may be intentionally or unintentionally released such as hydrogen

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Abstract

Un système et un procédé balayent une zone cible à une distance de 3 à 30 m pour un ou plusieurs matériaux. Le balayage est effectué par un faisceau d'émission cohérent dirigé à l'aide d'une caméra thermique. La source active du faisceau est un laser supercontinuum (SC). Le faisceau source émis est modulé par un spectromètre à transformée de Fourier à grande vitesse avant l'interaction avec la cible. Le faisceau source réfléchi cible est détecté par un détecteur infrarouge, conjointement avec une partie de référence du faisceau source émis, sous la forme d'une série d'interférogrammes ; passé à travers un numériseur pour numériser les interférogrammes ; et traité pour produire des spectrogrammes, les spectrogrammes indiquant un ou plusieurs matériaux sur la cible.
PCT/US2018/032623 2017-05-15 2018-05-15 Détection chimique à l'état de trace à distance par spectroscopie infrarouge active WO2018213212A1 (fr)

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Cited By (5)

* Cited by examiner, † Cited by third party
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EP3667296A1 (fr) * 2018-12-14 2020-06-17 The Boeing Company Système et procédé de détection optique
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GB2583377A (en) * 2019-04-26 2020-10-28 Univ Heriot Watt Systems and methods using active FTIR spectroscopy for detection of chemical targets
CN113984710A (zh) * 2021-10-27 2022-01-28 中国科学院半导体研究所 危险材料检测装置
CN113984710B (zh) * 2021-10-27 2024-06-07 中国科学院半导体研究所 危险材料检测装置

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US20200200675A1 (en) * 2018-10-30 2020-06-25 The Government Of The United States, As Represented By The Secretary Of The Navy Methods and apparatuses for biomimetic standoff detection of hazardous chemicals
US11774353B2 (en) * 2018-10-30 2023-10-03 The Government Of The United States Of America, As Represented By The Secretary Of The Navy Methods and apparatuses for biomimetic standoff detection of hazardous chemicals
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GB2583377A (en) * 2019-04-26 2020-10-28 Univ Heriot Watt Systems and methods using active FTIR spectroscopy for detection of chemical targets
WO2020217046A1 (fr) * 2019-04-26 2020-10-29 Heriot-Watt University Systèmes et procédés faisant appel à une spectroscopie ftir active pour la détection de cibles chimiques
US11867618B2 (en) 2019-04-26 2024-01-09 Heriot-Watt University Systems and methods using active FTIR spectroscopy for detection of chemical targets
CN113984710A (zh) * 2021-10-27 2022-01-28 中国科学院半导体研究所 危险材料检测装置
CN113984710B (zh) * 2021-10-27 2024-06-07 中国科学院半导体研究所 危险材料检测装置

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