We report on the design, modeling, calibration, and experimental results of a LWIR, spectrally and temporally resolved broad band bi-directional reflectance distribution function measuring device. The system is built using a commercial Fourier transform infrared spectrometer, which presents challenges due to relatively low power output compared to laser based methods. The instrument is designed with a sample area that is oriented normal to gravity, making the device suitable for measuring loose powder materials, liquids, or other samples that can be difficult to measure in a vertical orientation. The team built a radiometric model designed to understand the trade space available for various design choices as well as to predict instrument success at measuring the target materials. The radiometric model was built by using the output of commercial non sequential raytracing tools combined with a scripted simulation of the interferometer. The trade space identified in this analysis will be presented.
The design was based on moving periscopes with custom off axis parabolas to focus the light onto the sample. The system assembly and alignment will be discussed. The calibration method used for the sensor will be detailed, and preliminary measurements from this research sensor will be presented.
Validating predictive models and quantifying uncertainties inherent in the modeling process is a critical component of the HARD Solids Venture program [1]. Our current research focuses on validating physics-based models predicting the optical properties of solid materials for arbitrary surface morphologies and characterizing the uncertainties in these models. We employ a systematic and hierarchical approach by designing physical experiments and comparing the experimental results with the outputs of computational predictive models. We illustrate this approach through an example comparing a micro-scale forward model to an idealized solid-material system and then propagating the results through a system model to the sensor level. Our efforts should enhance detection reliability of the hyper-spectral imaging technique and the confidence in model utilization and model outputs by users and stakeholders.
Remote detection of a surface-bound chemical relies on the recognition of a pattern, or “signature,” that is distinct from the background. Such signatures are a function of a chemical’s fundamental optical properties, but also depend upon its specific morphology. Importantly, the same chemical can exhibit vastly different signatures depending on the size of particles composing the deposit. We present a parameterized model to account for such morphological effects on surface-deposited chemical signatures. This model leverages computational tools developed within the planetary and atmospheric science communities, beginning with T-matrix and ray-tracing approaches for evaluating the scattering and extinction properties of individual particles based on their size and shape, and the complex refractive index of the material itself. These individual-particle properties then serve as input to the Ambartsumian invariant imbedding solution for the reflectance of a particulate surface composed of these particles. The inputs to the model include parameters associated with a functionalized form of the particle size distribution (PSD) as well as parameters associated with the particle packing density and surface roughness. The model is numerically inverted via Sandia’s Dakota package, optimizing agreement between modeled and measured reflectance spectra, which we demonstrate on data acquired on five size-selected silica powders over the 4-16 μm wavelength range. Agreements between modeled and measured reflectance spectra are assessed, while the optimized PSDs resulting from the spectral fitting are then compared to PSD data acquired from independent particle size measurements.
This paper describes measurements being made on a series of material systems for the purpose of developing a radiative-transfer model that describes the reflectance of light by granular solids. It is well recognized that the reflectance spectra of granular materials depend on their intrinsic (n(λ) and k(λ)) and extrinsic (morphological) properties. There is, however, a lack of robust and proven models to relate spectra to these parameters. The described work is being conducted in parallel with a modeling effort1 to address this need. Each follows a common developmental spiral in which material properties are varied and the ability of the model to calculate the effects of the changes are tested. The parameters being varied include particle size/shape, packing density, material birefringence, optical thickness, and spectral contribution of a substrate. It is expected that the outcome of this work will be useful in interpreting reflectance data for hyperspectral imaging (HSI), and for a variety of other areas that rely on it.
Lucas Sweet, Edgar Buck, Charles Henager, Shenyang Hu, David Meier, Shane Peper, Jon Schwantes, Yin-Fong Su, Robert Sams, Thomas Blake, Timothy Johnson, Thomas Kulp, Ricky Sommers, Joshua Sugar, Jeffrey Chames
This work focuses on progress in gaining a better understanding of the polymorphic nature of the UO3 and UO3-water
system; one of several important materials associated with the nuclear fuel cycle. The UO3-water system is complex and
has not been fully characterized, even though these species are common throughout the fuel cycle. For example, most
production schemes for UO3 result in a mixture of up to six different polymorphic phases, and small differences in these
conditions will affect phase genesis that ultimately results in measureable changes to the end product. Here we
summarize our efforts to better characterize the UO3-water system with optical techniques for the purpose of developing
some predictive capability of estimating process history and utility, e.g. for polymorphic phases of unknown origin.
Specifically, we have investigated three industrially relevant production pathways of UO3 and discovered a previously
unknown low temperature route to β-UO3. Powder x-ray diffraction and optical spectroscopies were utilized in our
characterization of the UO3-water system. Pure phases of UO3, its hydrolysis products and starting materials were used
to establish optical spectroscopic signatures for these compounds. Preliminary aging studies were conducted on the α-
and γ- phases of UO3.
We describe a photofragment laser-induced fluorescence (PF-LIF) method that can be applied to the short-range-standoff
detection of low-volatility organophosphonate chemical warfare agents (OP-CWAs) on surfaces. It operates by
photofragmenting a surface-bound analyte and then actively interrogating a released phosphorous monoxide (PO)
fragment using LIF. We demonstrate a single-pulse-pair (pump = 500 μJ @ 266 nm; probe = 20 μJ @ 248 nm) surface
detection sensitivity of 30 μg/cm2 for the organophosphonate diisopropyl isothiocyanate phosphonate (DIPP) on
aluminum and 210 μg/cm2 for the same analyte on a more porous concrete surface. By detecting the PO photofragment,
the method indicates the presence of organophosphonates; however, we show that it also responds to other phosphorouscontaining
compounds. Because of its limited specificity, we believe that the method may have most immediate use as a
mapping tool to rapidly identify "hotspots" of OP-CWAs. These would then be confirmed using a more specific tool. As
one method of confirming the presence of OP-CWAs (and identifying the agent), we demonstrate that the probe beam
can be used to acquire Raman-scattering spectra of the target area.
As part of the U.S. Department of Homeland Security Detect-to-Protect (DTP) program, a multilab [Sandia National
Laboratories (SNL), Lawrence Livermore National Laboratories (LLNL), Pacific Northwest National Laboratory
(PNNL), Oak Ridge National Laboratory (ORNL), and Los Alamos National Laboratory (LANL)] effort is addressing
the need for useable detect-to-warn bioaerosol sensors for public facility protection. Towards this end, the SNL team is
investigating the use of rapid fluorogenic staining to infer the protein content of bioaerosols. This is being implemented
in a flow cytometer wherein each particle detected generates coincident signals of correlated forward scatter, side
scatter, and fluorescence. Several thousand such coincident signal sets are typically collected to generate a distribution
describing the probability of observing a particle with certain scattering and fluorescence values. These data are
collected for sample particles in both a stained and unstained state. A linear unmixing analysis is performed to
differentiate components in the mixture. In this paper, we discuss the implementation of the staining process and the
cytometric measurement, the results of their application to the analysis of known and blind samples, and a potential
instrumental implementations that would use staining.
As part of the U.S. Department of Homeland Security Detect-to-Protect program, a multilab [Sandia National
Laboratories (SNL), Lawrence Livermore National Laboratories (LLNL), Pacific Northwest National Laboratory
(PNNL), Oak Ridge National Laboratory (ORNL), and Los Alamos National Laboratory (LANL)] effort is addressing
the need for useable detect-to-warn bioaerosol sensors for public facility protection. Towards this end, the SNL team is
employing rapid fluorogenic staining to infer the protein content of bioaerosols. This is being implemented in a flow
cytometry platform wherein each particle detected generates coincident signals of forward scatter, side scatter, and
fluorescence. Several thousand such coincident signal sets are typically collected to generate a probability distribution
over the scattering and fluorescence values. A linear unmixing analysis is performed to differentiate components in the
mixture. After forming a library of pure component distributions from measured pure material samples, the distribution
of an unknown mixture of particles is treated as a linear combination of the pure component distributions. The
scattering/fluorescence probability distribution data vector a is considered the product of two vectors, the fractional
profile f and the scattering/fluorescence distributions from pure components P. A least squares procedure minimizes the
magnitude of the residual vector e in the expression a = fPT + e. The profile f designates a weighting fraction for each
particle type included in the set of pure components, providing the composition of the unknown mixture. We discuss
testing of this analysis approach and steps we have taken to evaluate the effect of interferents, both known and unknown.
The advent of novel quasi-phase matched materials based on patterned growth gallium arsenide offer the possibility of
broadly tunable IR sources covering the long- (5-12μm) and mid-wave (3-5μm) infrared spectral regions. From the
standpoint of chemical sensing, the long-wave infrared region between 8-12μm is attractive since it is an atmospheric
window, many functional groups absorb in this region and absorptions tend to be strong compared to the mid-IR. We
are employing orientation patterned GaAs as part of cw difference frequency spectrometer. In this system, light from
two, tunable external cavity diode lasers covering the 1.3μm and 1.5μm telecom bands was amplified then mixed in an
orientation- patterned GaAs crystal, producing radiation in the 7-9μm region. The system serves as a source for a cw
cavity ring-down spectrometer for ultra-trace gas detection applications. The combined tunability of the source,
coupled with the sensitivity of cavity ringdown spectroscopy will allow both detection and identification of a wide
range of species with unprecedented performance.
Lightsources employing quasiphasematched (QPM) nonlinear materials have demonstrated unique attributes for chemical sensing in the near- to mid-infrare spectral range (1 - 5 micrometers ). The advent of patterned-growth GaAs allows the first practical extension of QPM materials to operation in the long-wave IR (5 - 12 micrometers ). That wavelength range is particularly attractive for chemical sensing because it contains an atmospheric window, many molecular groups absorb there at distinct frequencies, and their absorptions tend to be strong relative to those in the near- and mid-IR. Here, the application of orientation-patterned GaAs (OPGaAs) for use in a continuous wave (cw) difference frequency spectrometer is described. The outputs of two external- cavity diode lasers operating in the 1.3 and 1.5 micrometers telecom bands are mixed in a OPGaAs crystal, producing tunable radiation at wavelengths near 8 micrometers . The application of the source to the measurement of a water vapor rovibrational absorption line is presented.
Photoacoustic spectroscopy is a sensitive, on-line and non- invasive tool to monitor concentrations of trace gases in ambient air. With the appropriate high power lasers in the mid-IR wavelength region gas mixtures can be analyzed, at and below the part per billion level. Within the development of novel IR laser sources, a continuous wave optical parametric oscillator based on periodically poled lithium niobate in combination with photoacoustic detection has been applied to detect traces of several hydrocarbons in nitrogen. At an idler wavelength of around 3.3 micrometers , the cw OPO produced approximately 300 mW of single mode radiation. Preliminary results show detection limits on methane, ethane, butane and pentane of around 1 ppb. This trace gas detector will be used within medical applications. E.g., the trace gas composition of exhaled air is able to give information about a wide variety of processes in human body. In addition, such analysis has the potential to monitor processes non-invasive, on-line and fast for diagnostic purposes related to acute or chronic diseases.
An infrared-imaging instrument is being developed to provide in situ qualitative and quantitative assessment of hydrocarbon contaminants on metallic surfaces for cleaning verification. A continuous-wave infrared optical parametric oscillator (OPO), based on the quasi-phasematched material periodically poled lithium niobate (PPLN), is interfaced with an InSb focal plane array camera to perform fast, non-invasive analysis by reflectance spectroscopy. The period range of the designed fan-out PPLN crystal determines the range of the output wavelength of the light source. It is able to scan hundreds of wavenumbers positioned in the range of 2820 - 3250 cm-1, which is sufficient to detect functional groups of common organic compounds (-CH, -OH, and -NH). The capability of the instrument has been demonstrated in a preliminary investigation of reflectance measurements for hydrocarbon solvents (methanol and d-limonene) on an aluminum surface. A substantial difference in absorption is obtained for the two solvents at two different laser-illumination wavelengths, thus permitting hydrocarbon detection and molecular species differentiation. Preliminary reflectance spectra of a mixture of aliphatic hydrocarbon lubricants and drawing agents on an aluminum panel are also presented. The relative thickness of the hydrocarbon thin film is determined by the intensity ratio of images acquired at two different laser illumination frequencies.
The development of a mid-infrared cavity ringdown spectrometer for trace gas measurements is described. The device employs a novel light source based on periodically poled lithium niobate (PPLN). Narrow linewidth (<EQ 0.08 cm-1 FWHM) mid-infrared radiation (at energies up to 15 (mu) J) is generated by three serial elements: a broadband optical parametric generator, a tunable spectral filter, and an optical parametric amplifier. Currently, spectral filtering is accomplished by an air-spaced Fabry-Perot etalon that allows 15 cm-1 of narrowband continuous tuning anywhere between 6200 - 6780 cm-1 and 3200 - 2620 cm-1. This can, in principle, be extended to the entire PPLN transparency window (2220 - 7690 cm-1) using multiple PPLN crystals and a suitable tuning element. The high gain of PPLN allows pumping by compact, high-repetition-rate solid-state laser sources, thereby minimizing the sensor size and allowing rapid spectral scans. Operation is demonstrated using both a 1 kHz Nd:YAG and a novel 120 Hz passively Q-switched Nd:YAG microlaser. Performance of the cavity ringdown sensor is characterized in terms of sensitivity, spectral coverage (segmented scans up to 350 cm-1 long), measurement speed, and measurements in the presence of atmospheric background gases. Issues relevant to the ultimate portable implementation of the sensor are addressed, including the use of two alternative frequency filtering/tuning mechanisms (a fiber-optic etalon and an acousto-optically tunable filter plus an air-speed etalon) and implementation of frequency calibration.
We report on a laser active imager suitable for the visualization of natural gas leaks and volatile organic compounds emitted by oil refineries. The described backscatter-absorption gas-imaging (BAGI) system employs a raster scanner in conjunction with a tunable continuous wave (cw) laser source. The imager creates real-time video imagery of a scene, while illuminating it with infrared laser light at a wavelength that is absorbed by the gas to be detected. Thus, gas plumes that otherwise cannot be seen by the human eye appear in BAGI images as dark clouds. In order to produce the high intensity infrared light that is needed to image natural gas and refinery by-products, we used a nonlinear frequency-conversion technique that employs the quasi-phase-matched crystal periodically poled LiNbO3. The crystal serves as the active medium in a cw optical parametric oscillator (OPO) that is pumped by a diode-pumped Nd:YAG laser. The output frequencies were selected to coincide with absorption features of general aliphatic species (2935 and 2968 cm-1), aromatics, such as benzene and toluene (3033 cm-1), and methane (3018 cm-1). The crystal was engineered to cover the desired spectral range using a fan-out design. This allows tuning of the OPO between 2832 and 3145 cm-1 in idler wavelength by simply translating the crystal at a fixed temperature. Presented data demonstrate the performance of this system for imaging species of interest at relevant concentrations and ranges up to about 30 m.
Laser-based sensors, currently under development and testing at Sandia National Laboratories for process control, emissions monitoring, and pollution prevention, are discussed.
Backscatter gas absorption imaging (BAGI) has been demonstrated as a useful technique for visualizing gas leaks. BAGI uses active imaging in the infrared to generate a laser- illuminated video image of a scene. A dark cloud in the image is formed when a gas absorbs the illuminating laser radiation in the vicinity of the plume. The sensitivity of the technique is limited by the ability of the operator to distinguish scene contrasts from gas contrasts. To improve its performance, we have developed a differential absorption system to subtract off scene contrasts that can obscure a gas plume. This system is essentially an imaging differential absorption LIDAR (DIAL) that allows one to focus on contrast in a scene due to absorption from a gas plume instead of contrast due to variations in the reflectivity of the target. Practical aspects of this system are presented along with results taken in real-world settings. The noise floor for a differential image is shown to be dominated by uncorrelated speckle fluctuations -- not contrasts in the scene.
The results of field tests of an active backscatter absorption gas imaging (BAGI) system and a passive imager based on a Ga:Si infrared focal-plane array are presented. Both imagers allow real-time video imaging of gas emissions. The former system images gases through their attenuation of backscattered laser illumination; the latter images gases through temperature or emissivity differences. The results represent the first side-by-side comparison of an active and passive imager and the first BAGI field trial involving the imaging of plumes of controlled concentration and dimension.
The means to detect, visualize and survey different kinds of gases within industrial and energy processes, technical infrastructure, landfill bodies, indoor and outdoor environment are discussed. The current status and future plans for IR imaging technologies in the U.S. and in Sweden are described. Primary consideration is given to mobile and airborne remote sensing systems, such as current laser-based imaging technologies, advanced IR systems with and without filter techniques, and two-dimensional gas-correlation techniques, being used or under development. Results of recent laboratory and field experiments involving the imaging of natural gas leaks under both controlled and actual conditions are presented and discussed. Plans for future field testing and technology improvements are described.
In this paper, we summarize the design and preliminary performance evaluation of a new raster-scanning BAGI imager that is intended for long-range operation, at a target range of 300 m. A system capable of imaging at this range is desired to make airborne gas imaging from a low-flying airplane or helicopter possible. The system uses a 20 W CO2 laser and a redesigned scanner that employs telescopic transmission and receiving optics. Model predictions of the performance of the new system and some recent field testing results are presented. Issues relating to gas imaging at long ranges are also discussed.
The design and construction of a synchronous-scanning underwater imaging system capable of rapid two-dimensional scanning is described. The imager employs a 7 W all-lines argon ion laser in conjunction with a galvanometrically driven raster scanner and an image-dissector tube receiver. The imager is capable of directly generating real-time RS-170 video imagery. The results of in-water test of the imaging system demonstrate operating ranges of up to 4 attenuation lengths (AL) when running at real-time frame rates, ranges of 5.1 - 5.5 AL when operating with an 8-frame running average, and ranges of 6.3 AL when using a 128-frame running average. Future frame averaging requirements are expected to be relaxed, due to improvements in the detector preamplifier. The system performance was compared with that of several floodlight/silicon intensified target (SIT) television camera configurations, which produced a maximum imaging range of about 2.6 AL. Also, an imaging configuration that used the raster-scanned beam of the laser as an illumination source for the SIT camera was tested. That system had an ultimate range of about 4 AL.
The application of backscatter absorption gas imaging (BAGI) to the detection of gaseous chemical species associated with the production of illegal drugs is considered. BAGI is a gas visualization technique that allows the imaging of over 70 organic vapors at minimum concentrations of a few to several hundred ppm-m. Present BAGI capabilities at Lawrence Livermore National Laboratory and Laser Imaging Systems are discussed. Eighteen different species of interest in drug-law enforcement are identified as being detectable by BAGI. The chemical remote sensing needs of law enforcement officials are described, and the use of BAGI in meeting some of these needs is outlined.
This report provides a summary of the second in-water test of the
LLNL/NAVSEA Underwater Laser Imaging System (UWLIS). The UWLIS is a
laser-based, synchronous-scanning, underwater imaging device that is
designed to operate at greater ranges than is possible with conventional underwater TV cameras. It differs from earlier prototype synchronousscanning systems in that it is capable of high scan rates that allow the generation of real-time, RS-170 video images. The UWLIS is being developed for eventual use on Remotely Operated Vehicles (ROVs) during deep-ocean Naval salvage missions. The floodlight-illuminated television cameras presently used on NAVSEA vessels can produce images at ranges up to about 2 attenuation lengths (AL) (2). Beyond that point, common volume backscatter from particulates in the intervening seawater between the imager and the target overwhelms the return signal, and the image is lost. The special optical geometry of the synchronous-scanning imager is
designed to minimize common-volume effects. Previous theoretical studies (1) indicate that a system of this type should be capable of operation at distances as great as 6 to 7 attenuation lengths. An improvement of this magnitude would greatly increase the efficiency of salvage operations, thus decreasing their cost.
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