This PDF file contains the front matter associated with SPIE Proceedings Volume 9101, including the Title Page, Copyright information, Table of Contents, Invited Panel Discussion, and Conference Committee listing.

With a trend towards the use of spectroscopic systems in various fields of science and industry, there is an increasing demand for compact spectrometers. For UV/VIS to the shortwave near-infrared spectral range, compact hand-held polychromator type devices are widely used and have replaced larger conventional instruments in many applications. Still, for longer wavelengths this type of compact spectrometers is lacking suitable and affordable detector arrays. In perennial development Carinthian Tech Research AG together with the Fraunhofer Institute for Photonic Microsystems endeavor to close this gap by developing spectrometer systems based on photonic MEMS. Here, we review on two different spectrometer developments, a scanning grating spectrometer working in the NIR and a FT-spectrometer accessing the mid-IR range up to 14 μm. Both systems are using photonic MEMS devices actuated by in-plane comb drive structures. This principle allows for high mechanical amplitudes at low driving voltages but results in gratings respectively mirrors oscillating harmonically. Both systems feature special MEMS structures as well as aspects in terms of system integration which shall tease out the best possible overall performance on the basis of this technology. However, the advantages of MEMS as enabling technology for high scanning speed, miniaturization, energy efficiency, etc. are pointed out. Whereas the scanning grating spectrometer has already evolved to a product for the point of sale analysis of traditional Chinese medicine products, the purpose of the FT-spectrometer as presented is to demonstrate what is achievable in terms of performance. Current developments topics address MEMS packaging issues towards long term stability, further miniaturization and usability.

OPTRA has developed a Fourier transform infrared phase shift cavity ring down spectrometer (FTIR-PS-CRDS) system under a U.S. EPA SBIR contract. This system uses the inherent wavelength-dependent modulation imposed by the FTIR on a broadband thermal source for the phase shift measurement. This spectrally-dependent phase shift is proportional to the spectrally-dependent ring down time. The spectral dependence of both of these values is introduced by the losses of the cavity including those due to the molecular absorption of the sample. OPTRA’s approach allows broadband detection of chemicals across the feature-rich fingerprint region of the long-wave infrared. This represents a broadband and spectral range enhancement to conventional CRDS which is typically done at a single wavelength in the near IR; at the same time the approach is a sensitivity enhancement to traditional FTIR, owing to the long effective path of the resonant cavity. In previous papers^1,2, OPTRA has presented a breadboard system aimed at demonstrating the feasibility of the approach and a prototype design implementing performance enhancements based on the results of breadboard testing. In this final paper in the series, we will present test results illustrating the realized performance of the fully assembled and integrated breadboard, thereby demonstrating the utility of the approach.

Traditional Fabry-Perot (FP) spectroscopy is bandwidth limited to avoid mixing signals from different transmission orders of the interferometer. Unlike Fourier transformation, the extraction of spectra from multiple-order interferograms resulting from multiplexed optical signals is in general an ill-posed problem. Using a Fourier transform approach, we derive a generalized Nyquist limit appropriate to signal recovery from FP interferograms. This result is used to derive a set of design rules giving the usable wavelength range and spectral resolution of FP interferometers or etalon arrays given a set of accessible physical parameters. Numerical simulations verify the utility of these design rules for moderate resolution spectroscopy with bandwidths limited by the detector spectral response. Stable and accurate spectral recovery over more than one octave is accomplished by simple matrix multiplication of the interferogram. In analogy to recently developed single-order micro-etalon arrays (Proc. of SPIE v.8266, no. 82660Q), we introduce Multiple-Order Staircase Etalon Spectroscopy (MOSES), in which micro-arrays of multiple order etalons can be bonded to or co-fabricated with a sensor array. MOSES enables broader bandwidth multispectral and hyperspectral instruments than single-order etalon arrays while keeping a physical footprint insignificantly different from that of the detection array.

Spectrometers are widely used tools in chemical and biological sensing, material analysis, and light source characterization. The development of a high-resolution on-chip spectrometer could enable compact, low-cost spectroscopy for portable sensing as well as increasing lab-on-a-chip functionality. However, the spectral resolution of traditional grating-based spectrometers scales with the optical pathlength, which translates to the linear dimension or footprint of the system, which is limited on-chip. In this work, we utilize multiple scattering in a random photonic structure fabricated on a silicon chip to fold the optical path, making the effective pathlength much longer than the linear dimension of the system and enabling high spectral resolution with a small footprint. Of course, the random spectrometer also requires a different operating paradigm, since different wavelengths are not spatially separated by the random structure, as they would be by a grating. Instead, light transmitted through the random structure produces a wavelengthdependent speckle pattern which can be used as a fingerprint to identify the input spectra after calibration. In practice, these wavelength-dependent speckle patterns are experimentally measured and stored in a transmission matrix, which describes the spectral-to-spatial mapping of the spectrometer. After calibrating the transmission matrix, an arbitrary input spectrum can be reconstructed from its speckle pattern. We achieved sub-nm resolution with 25 nm bandwidth at a wavelength of 1500 nm using a scattering medium with largest dimension of merely 50 μm.

Microplasmas are receiving increasing attention in the scientific literature and in recent conferences. Yet, few analytical applications of microplasmas for elemental analysis using liquid samples have been described in the literature. To address this, we describe two applications: one involves the determination of Zn in microsamples of the metallo-enzyme Super Oxide Dismutase. The other involves determination of Pd-concentration in microsamples of Pd nanocatalysts. These applications demonstrate the potential of microplasmas and point to the need for future fundamental studies.

Sorbent materials are utilized in a range of analytical applications including coatings for preconcentrator devices, chromatography stationary phases, and as thin film transducer coatings used to concentrate analyte molecules of interest for detection. In this work we emphasize the use of sorbent materials to target absorption of analyte vapors and examine their molecular interaction with the sorbent by optically probing it with infrared (IR) light. The complex spectral changes which may occur during molecular binding of specific vapors to target sites in a sorbent can significantly aid in analyte detection. In this work a custom hydrogen-bond (HB) acidic polymer, HCSFA2, was used as the sorbent. HCSFA2 exhibits a high affinity for hazardous vapors with hydrogen-bond (HB) basic properties such as the G-nerve agents. Using bench top ATR-FTIR spectroscopy the HFIP hydroxyl stretching frequency has been observed in the mid wave infrared (MWIR) to shift by up to 700 wavenumbers when exposed to a strong HB base. The amount of shift is related to the HB basicity of the vapor. In addition, the large analyte polymer-gas partition coefficients sufficiently concentrate the analyte in the sorbent coating to allow spectral features of the analyte to be observed in the MWIR and long wave infrared (LWIR) while it is sorbed to HCSFA2. These spectral changes, induced by analyte-sorbent molecular binding, provide a rich signal feature space to consider selective detection of a wide range of chemical species as single components or complex mixtures. In addition, we demonstrate an HCSFA2 coated microbridge structure and micromechanical photothermal spectroscopy to monitor spectral changes when a vapor sorbs to HCSFA2. Example ATR-FTIR and microbridge spectra with exposures to dimethylmethylphosphonate (DMMP – G nerve agent simulant) and other vapors are compared. In a generic form we illustrate the concept of this work in Figure 1. The results of this work provide the potential to consider compact detection systems with high detection fidelity.

While optical spectroscopy has shown great promise in a multitude of applications, the cost, size, and fragility of spectrometer instruments have hindered widespread application of the technology. :tvfEMS microspectrometers offer great hope for low-cost, lightweight, and robust spectrometers, paving the way for pervasive use in many fields. In this invited paper, we report on nearly 15 years of development on MEMS spectrometers in our research group, beginning with devices designed for the shortwave infrared (SWIR) and midwave infrared (MWIR), and moving on to our most recent work towards MEMS spectrometers in the visible and near infrared (NIR) as well as the thermal long-wave infrared (LWIR) bands.

One of the important challenges for widespread application of MOEMS devices is to provide a modular interface for easy handling and accurate driving of the MOEMS elements, in order to enable seamless integration in larger spectroscopic system solutions. In this contribution we present in much detail the optical design of MOEMS driver modules comprising optical position sensing together with driver electronics, which can actively control different electrostatically driven MOEMS. Furthermore we will present concepts for compact spectroscopic devices, based on different MOEMS scanner modules with lD and 2D optical elements.

The next generation of multispectral instruments requires significant improvements in both spectral band customization and portability to support the widespread deployment of application-specific optical sensors. The benefits of spectroscopy are well established for numerous applications including biomedical instrumentation, industrial sorting and sensing, chemical detection, and environmental monitoring. In this paper, spectroscopic (and by extension hyperspectral) and multispectral measurements are considered. The technology, tradeoffs, and application fits of each are evaluated. In the majority of applications, monitoring 4-8 targeted spectral bands of optimized wavelength and bandwidth provides the necessary spectral contrast and correlation. An innovative approach integrates precision spectral filters at the photodetector level to enable smaller sensors, simplify optical designs, and reduce device integration costs. This method supports user-defined spectral bands to create application-specific sensors in a small footprint with scalable cost efficiencies. A range of design configurations, filter options and combinations are presented together with typical applications ranging from basic multi-band detection to stringent multi-channel fluorescence measurement. An example implementation packages 8 narrowband silicon photodiodes into a 9x9mm ceramic LCC (leadless chip carrier) footprint. This package is designed for multispectral applications ranging from portable color monitors to purpose- built OEM industrial and scientific instruments. Use of an eight-channel multispectral photodiode array typically eliminates 10-20 components from a device bill-of-materials (BOM), streamlining the optical path and shrinking the footprint by 50% or more. A stepwise design approach for multispectral sensors is discussed – including spectral band definition, optical design tradeoffs and constraints, and device integration from prototype through scalable volume production. Additional customization options are explored for application-specific OEM sensors integrated into portable devices using multispectral photodiode arrays.

Pure rotational spectroscopy in the centimeter, millimeter, and THz regions of the electromagnetic spectrum is a powerful technique for the characterization of polar molecules in the gas phase. Although this technology has a long history in the research sector for structural characterization, recent advances in digital electronics have only recently made commercial instruments competitive with established chemical analysis techniques. BrightSpec is introducing a platform of pure rotational spectrometers in response to critical unmet needs in chemical analysis. These instruments aim to deliver the operational simplicity of Fourier transform infrared spectrometers in conjunction with the chemical analysis capabilities of mass spectrometers. In particular, the BrightSpec ONE instrument a broadband gas mixture analyzer with full capabilities for chemical analysis. This instrument implements Fourier transform millimeter-wave emission spectroscopy, wherein a brief excitation pulse is applied to the sample, followed by the measurement of the coherent free induction decay responses of all molecular transitions within the excitation bandwidth. After sample injection and characterization, the spectrometer returns a list of all known species detected in the sample, along with their concentrations in the mixture. No prior knowledge about the sample composition is required. The instrument can then perform double-resonance measurements (analogous to 2-D COSY NMR), direct mass determination through analysis of the time profile of the molecular signal, and automated isotopic identification as part of a suite of tools that can return the structural identity of the unknowns in the sample.

Miniaturization and cost reduction of spectrometer and sensor technologies has great potential to open up new applications areas and business opportunities for analytical technology in hand held, mobile and on-line applications. Advances in microfabrication have resulted in high-performance MEMS and MOEMS devices for spectrometer applications. Many other enabling technologies are useful for miniature analytical solutions, such as silicon photonics, nanoimprint lithography (NIL), system-on-chip, system-on-package techniques for integration of electronics and photonics, 3D printing, powerful embedded computing platforms, networked solutions as well as advances in chemometrics modeling. This paper will summarize recent work on spectrometer and sensor miniaturization at VTT Technical Research Centre of Finland. Fabry-Perot interferometer (FPI) tunable filter technology has been developed in two technical versions: Piezoactuated FPIs have been applied in miniature hyperspectral imaging needs in light weight UAV and nanosatellite applications, chemical imaging as well as medical applications. Microfabricated MOEMS FPIs have been developed as cost-effective sensor platforms for visible, NIR and IR applications. Further examples of sensor miniaturization will be discussed, including system-on-package sensor head for mid-IR gas analyzer, roll-to-roll printed Surface Enhanced Raman Scattering (SERS) technology as well as UV imprinted waveguide sensor for formaldehyde detection.

The success of a commercial fluorescent diagnostic assay is dependent on the selection of a fluorescent biomarker; due to the broad nature of fluorescence biomarker emission profiles, only a small number of fluorescence biomarkers may be discriminated from each other as a function of excitation source. Multivariate Optical Elements (MOEs) are thin-film devices that encode a broad band, spectroscopic pattern allowing a simple broadband detector to generate a highly sensitive and specific detection for a target analyte. MOEs have historically been matched 1:1 to a discrete analyte or class prediction; however, MOE filter sets are capable of sensing projections of the original sparse spectroscopic space enabling a small set of MOEs to discriminate a multitude of target analytes. This optical regression can offer real-time measurements with relatively high signal-to-noise ratios that realize the advantages of multiplexed detection and pattern recognition in a simple optical instrument. The specificity advantage of MOE-based sensors allows fluorescent biomarkers that were once incapable of discrimination from one another via optical band pass filters to be employed in a common assay panel. A simplified MOE-based sensor may ultimately reduce the requirement for highly trained operators as well as move certain life science applications like disease prognostication from the laboratory to the point of care. This presentation will summarize the design and fabrication of compressed detection MOE filter sets for detecting multiple fluorescent biomarkers simultaneously with strong spectroscopic interference as well as comparing the detection performance of the MOE sensor with traditional optical band pass filter methodologies.

Nanophotonic structures including photonic crystals and plasmonics have a lot of potential applications in spectral sensing. These devices typically require electron beam lithography, a slow process, for fabrication. Successful commercialization of these technologies requires reproducible, high volume fabrication. Projection lithography is an established process for rapid, reproducible patterning. We have successfully pushed the limits of projection lithography to develop a low-cost, high-throughput alternative to electron beam lithography for our nanoscale, visible-wavelength photonic crystal spectral sensors. The developed process is 100 times faster than electron beam lithography for 10mm by 10mm dies on a four inch wafer. Testing of the photonic crystals in spectral sensors shows uniformity in large scale production which is robust to defects from processing.

In recent years the importance of lasers in optical gas sensing has been continuously increasing. Tunable Laser Absorption Spectroscopy (TLAS) has proven to be a versatile tool in modern environmental analysis. In the mid-infrared wavelength region between 3 and 6 µm, which is of high interest for sensing applications, Interband Cascade Lasers (ICL) can provide monomode continuous wave (CW) emission at room temperature. We present the simulation, design and manufacturing of distributed feedback (DFB) laser devices based on this concept, with focus on devices that target specific, technologically and industrially relevant, wavelengths with low energy consumption. Finally application-grade devices from 3 to 6 µm are presented. CW operation above room temperature and tuning ranges of 11 nm with Side Mode Suppression Ratios (SMSR) greater 30 dB were achieved.

To reduce atmospheric accumulation of the greenhouse gases methane and carbon dioxide, networks of continuously operating sensors that monitor and map their sources are desirable. In this paper, we discuss advances in laser-based open-path leak detectors, as well as technical and economic challenges inhibiting widespread sensor deployment for “ubiquitous monitoring”. We describe permanently-installed, wireless, solar-powered sensors that overcome previous installation and maintenance difficulties while providing autonomous real-time leak reporting without false alarms.

Quantum cascade lasers (QCLs) and Interband cascade lasers (ICLs) are promising new mid-IR sources for spectroscopic applications. Desirable characteristics include extremely high brightness, broad emission, very high resolution, compact size, and modest power consumption. For most spectroscopic applications, it is necessary to tune QCLs over a broad emission wavelength range. The conventional approach for broad tuning is to use an external cavity (EC) which incorporates a mechanically tuned diffraction grating within the laser cavity. In this paper we will describe an alternative approach to EC-QCL tuning which utilizes miniature, thermally tuned, MEMS fabricated filters, allowing for a very compact, simple, mechanically stable package with no moving parts. The system is well suited for discrete measurements at multiple wavelengths as needed by many of the industrial spectroscopic analyzers in use today. An accuracy of 0.02 cm^-1 over the 50 cm^-1 range of the test laser and a precision of 0.002 cm^-1 over a 15 cm^-1 scan has been demonstrated. High resolution mode hop free CW scanning of a 0.5 cm^-1 range at a scan rate of 200 Hz with a wavelength precision of 0.002 cm^-1 has also been demonstrated. This makes the design an attractive alternative to current Distributed feedback (DFB) QCLs for high resolution gas phase measurements due to the added advantage of broad tunability for the detection of multiple gases, and the capability to select multiple gas lines of different intensity to extend the dynamic range.

There is a need to identify the source of origin for many items of military interest, including ammunition and weapons that may be circulated and traded in illicit markets. Both fieldable systems (man-portable or handheld) as well as benchtop systems in field and home base laboratories are desired for screening and attribution purposes. Laser Induced Breakdown Spectroscopy (LIBS) continues to show significant capability as a promising new tool for materials identification, matching, and provenance. With the use of the broadband, high resolution spectrometer systems, the LIBS devices can not only determine the elemental inventory of the sample, but they are also capable of elemental fingerprinting to signify sources of origin of various materials. We present the results of an initial study to differentiate and match spent cartridges from different manufacturers and countries. We have found that using Partial Least Squares Discriminant Analysis (PLS-DA) we are able to achieve on average 93.3% True Positives and 5.3% False Positives. These results add to the large body of publications that have demonstrated that LIBS is a particularly suitable tool for source of origin determinations.

Alloy identification of oil-borne wear debris captured on chip detectors, filters and magnetic plugs allows the machinery maintainer to assess the health of the engine or gearbox and identify specific component damage. Today, such identification can be achieved in real time using portable, at-line laser-induced breakdown spectroscopy (LIBS) and Xray fluorescence (XRF) instruments. Both techniques can be utilized in various industries including aviation, marine, railways, heavy diesel and other industrial machinery with, however, some substantial differences in application and instrument performance. In this work, the performances of a LIBS and an XRF instrument are compared based on measurements of a wide range of typical aerospace alloys including steels, titanium, aluminum and nickel alloys. Measurement results were analyzed with a staged correlation technique specifically developed for the purposes of this study - identifying the particle alloy composition using a pre-recorded library of spectral signatures. The analysis is performed in two stages: first, the base element of the alloy is determined by correlation with the stored elemental spectra and then, the alloy is identified by matching the particle’s spectral signature using parametric correlation against the stored spectra of all alloys that have the same base element. The correlation analysis has achieved highly repeatable discrimination between alloys of similar composition. Portable LIBS demonstrates higher detection accuracy and better identification of alloys comprising lighter elements as compared to that of the portable XRF system, and reveals a significant reduction in the analysis time over XRF.

Copper concentrations in drinking-water is very important to be monitored which can cause cancer if it exceed about 10 mg/liter. In the present work, we have developed a simple, low laser power method to improve the detection limits of laser induced plasma spectroscopy LIBS for copper in aqueous solutions with different concentrations. In this method a medium density fiberboard (MDF) wood have been used as a substrate that absorbs the liquid sample to transform laser liquid interaction to laser solid interaction. Using the fundamental wavelength of Nd:YAG laser, the constructed plasma emissions were monitored for elemental analysis. The signal-to-noise ratio SNR was optimized using low laser fluence of 32 J cm^-2, and detector (CDD camera) gate delay of 0.5 μs. Both the electron temperature and density of the induced plasma were determined using Boltzmann plot and the FWHM of the Cu at 324.7 nm, respectively. The plasma temperature was found to be 1.197 eV, while the plasma density was about 1.66 x 1019 cm^-3. The detection limits for Cu at 324.7 nm is found to be 131 ppb comparable to the results by others using complicated system.

There exists an unmet need in the discovery and identification of certain improvised explosive (IE) materials. IE contain a wide range of materials, many of which are not well classified by available hand-held tools, especially metal powders and food products. Available measurement approaches are based in the identification of specific subgroups such as nitro/nitrate and chlorate/perchlorate, normally with Raman spectroscopy. The presence of metal powders is not detected by these approaches, and further the powders themselves scatter the laser radiation used in the excitation of the spectra, making other components more difficult to discern. Preliminary work with laserinduced breakdown spectroscopy (LIBS) shows that metal powders are easily detected and identified, and that fuel compounds in flash powder mixtures are easily classified with principal component analysis into those containing oxygen and chlorine or those containing oxygen and nitrogen. Alkali and alkali metal signals are readily used to determine the cation of any salt submitted to analysis.

While significant progress has been made towards the miniaturization of Raman, mid-infrared (IR), and near-infrared (NIR) spectrometers for homeland security and law enforcement applications, there remains continued interest in pushing the technology envelope for smaller, lower cost, and easier to use analyzers. In this paper, we report on the use of the MicroNIR Spectrometer, an ultra-compact, handheld near infrared (NIR) spectrometer, the, that weighs less than 60 grams and measures < 50mm in diameter for the classification of 140 different substances most of which are controlled substances (such as cocaine, heroin, oxycodone, diazepam), as well as synthetic cathinones (also known as bath salts), and synthetic cannabinoids. A library of the materials was created from a master MicroNIR spectrometer. A set of 25 unknown samples were then identified with three other MicroNIRs showing: 1) the ability to correctly identify the unknown with a very low rate of misidentification, and 2) the ability to use the same library with multiple instruments. In addition, we have shown that through the use of innovative chemometric algorithms, we were able to identify the individual compounds that make up an unknown mixture based on the spectral library of the individual compounds only. The small size of the spectrometer is enabled through the use of high-performance linear variable filter (LVF) technology.

Raman spectroscopy is a widely used spectroscopic technique with a number of applications. During the past few years, we explored the use of simultaneous multiple-excitation-wavelengths (MEW) in resonance Raman spectroscopy. This approach takes advantage of Raman band intensity variations across the Resonance Raman spectra obtained from two or more excitation wavelengths. Amplitude variations occur between corresponding Raman bands in Resonance Raman spectra due to complex interplay of resonant enhancement, self-absorption and laser penetration depth. We have developed a very sensitive algorithm to estimate concentration of an analyte from spectra obtained using the MEW technique. The algorithm uses correlations and least-square minimization approach to calculate an estimate for the concentration. For two or more excitation wavelengths, measured spectra were stacked in a two dimensional matrix. In a simple realization of the algorithm, we approximated peaks in the ideal library spectra as triangles. In this work, we present the performance of the algorithm with measurements obtained from a dual-excitation-wavelength Resonance Raman sensor. The novel sensor, developed at WVHTCF, detects explosives from a standoff distance. The algorithm was able to detect explosives with very high sensitivity even at signal-to-noise ratios as low as ~1.6. Receiver operating characteristics calculated using the algorithm showed a clear benefit in using the dual-excitation-wavelength technique over single-excitation-wavelength techniques. Variants of the algorithm that add more weight to amplitude variation information showed improved specificity to closely resembling spectra.

Raman spectroscopy is the technology of choice to identify bulk solid and liquid phase unknown samples without the need to contact the substance. Materials can be identified through transparent and semi-translucent containers such as plastic and glass. ConOps in emergency response and military field applications require the redesign of conventional laboratory units for: field portability; shock, thermal and chemical attack resistance; easy and intuitive use in restrictive gear; reduced size, weight, and power. This article introduces a new handheld instrument (ACE-ID^TM) designed to take Raman technology to the next level in terms of size, safety, speed, and analytical performance. ACE-ID is ruggedized for use in severe climates and terrains. It is lightweight and can be operated with just one hand. An intuitive software interface guides users through the entire identification process, making it easy-to-use by personnel of different skill levels including military explosive ordinance disposal technicians, civilian bomb squads and hazmat teams. Through the use of embedded advanced algorithms, the instrument is capable of providing fluorescence correction and analysis of binary mixtures. Instrument calibration is performed automatically upon startup without requiring user intervention. ACE-ID incorporates an optical rastering system that diffuses the laser energy over the sample. This important innovation significantly reduces the heat induced in dark samples and the probability of ignition of susceptible explosive materials. In this article, the explosives identification performance of the instrument will be provided in addition to a quantitative evaluation of the safety improvements derived from the reduced ignition probabilities.

Portable Raman analyzers have emerged during the first part of this century as an important field tool for crime scene and forensic analysis, primarily for their ability to identify unknown substances. This ability is also important to the US military, which has been investigating such analyzers for identification of explosive materials that may be used to produce improvised explosive devices, chemicals that may be used to produce chemical warfare agents, and fuels in storage tanks that may be used to power US military vehicles. However, the use of such portable analyzers requires that they meet stringent military standards (specifically MIL-STD 810G). These requirements include among others: 1) light weight and small size (< 35 pounds, < 3 cu. ft.), 2) vibration and shock resistant (26 four foot drops), 3) operation from -4 to 110 ^oF, 4) operation in blowing dust, sand and rain, 5) battery operation, and of course 6) safe operation (no laser or shock hazards). Here we describe a portable Raman analyzer that meets all of these requirements, and its use to determine if captured fuels are suitable for use.

Raman spectroscopy is a powerful technique for material identification. The technique is sensitive to primary and higher ordered molecular structure and can be used to identify unknown materials by comparison with spectral reference libraries. Additionally, miniaturization of opto-electronic components has permitted development of portable Raman analyzers that are field deployable. Raman scattering is a relatively weak effect compared to a competing phenomenon, fluorescence. Even a moderate amount of fluorescence background interference can easily prevent identification of unknown materials. A long wavelength Raman system is less likely to induce fluorescence from a wider variety of materials than a higher energy visible laser system. Compounds such as methyl salicylate (MS), diethyl malonate (DEM), and dimethyl methylphosphonate (DMMP) are used as chemical warfare agent (CWA) simulants for development of analytical detection strategies. Field detection of these simulants however poses unique challenges because threat identification must be made quickly without the turnaround time usually required for a laboratory based analysis. Fortunately, these CWA simulants are good Raman scatterers, and field based detection using portable Raman instruments is promising. Measurements of the CWA simulants were done using a 1064 nm based portable Raman spectrometer. The longer wavelength excitation laser was chosen relative to a visible based laser systems because the 1064 nm based spectrometer is less likely to induce fluorescence and more suitable to a wider range of materials. To more closely mimic real world measurement situations, different sample presentations were investigated.

The hyperspectral thermal emission spectrometer was developed under NASA’s instrument incubator program and has now completed three deployments. The scan head uses a state-of-the-art Dyson spectrometer cooled to 100K coupled to a quantum well infrared photodetector array held at 40K. The combination allows for 256 spectral channels between 7.5μm and 12μm with 512 cross track spatial pixels. Spectral features for many interesting gases fall within the instrument passband. We first review the pre-flight calibration and validation process for HyTES using a suite of instrumentation. This includes a smile measurement at two wavelengths (8.18μm and 10.6μm) as well as a concentration determination using large aperture gas cells. We then show positive gas plume detection at ranges >1000m for various cases: Ammonia gas detection from Salton Sea fumaroles, Methane detection from staged releases points in Wyoming as well as naturally occurring methane hot spots off the coast of Santa Barbara.

A miniaturized hyperspectral imager is enabled with image sensor integrated with dispersing elements in a very compact form factor, removing the need for expensive, moving, bulky and complex optics that have been used in conventional hyperspectral imagers for decades. The result is a handheld spectral imager that can be installed on miniature UAV drones or conveyor belts in production lines. Eventually, small handhelds can be adapted for use in outpatient medical clinics for point-of-care diagnostics and other in-field applications.

Tornado Spectral Systems (TSS) has developed High Throughput Virtual Slit (HTVS) technology that improves the performance of spectrometers by factors of several while maintaining system size. In the simplest configuration, the HTVS allows optical designers to remove the lossy slit from a spectrometer, greatly increasing throughput without a loss of resolution. This is especially useful in many standoff applications, where every photon matters. TSS has tested multiple configurations of HTVS spectral sensing and spectral imaging technology, including standoff sensing, point scan imaging, long-slit pushbroom imaging and similar configurations. The HTVS throughput-resolution advantage allows us to increase scanning speed, decrease system size, decrease aperture, decrease source intensity requirements or some combination of all four. HTVS technology expands the realm of viable spectral imaging applications. We discuss the applicability of this technology to spectral imaging and standoff sensing and present experimental results from several prototype and production spectrometers.

The need for standoff detection technology to provide early Chem-Bio (CB) threat warning is well documented. Much of the information obtained by a single passive sensor is limited to bearing and angular extent of the threat cloud. In order to obtain absolute geo-location, range to threat, 3-D extent and detailed composition of the chemical threat, fusion of information from multiple passive sensors is needed. A capability that provides on-the-move chemical cloud characterization is key to the development of real-time Battlespace Awareness. We have developed, implemented and tested algorithms and hardware to perform the fusion of information obtained from two mobile LWIR passive hyperspectral sensors. The implementation of the capability is driven by current Nuclear, Biological and Chemical Reconnaissance Vehicle operational tactics and represents a mission focused alternative of the already demonstrated 5-sensor static Range Test Validation System (RTVS).1 The new capability consists of hardware for sensor pointing and attitude information which is made available for streaming and aggregation as part of the data fusion process for threat characterization. Cloud information is generated using 2-sensor data ingested into a suite of triangulation and tomographic reconstruction algorithms. The approaches are amenable to using a limited number of viewing projections and unfavorable sensor geometries resulting from mobile operation. In this paper we describe the system architecture and present an analysis of results obtained during the initial testing of the system at Dugway Proving Ground during BioWeek 2013.

Chemical micro-imaging is a powerful tool for the detection and identification of analytes of interest against a cluttered background (i.e. trace explosive particles left behind in a fingerprint). While a variety of groups have demonstrated the efficacy of Raman instruments for these applications, point by point or line by line acquisition of a targeted field of view (FOV) is a time consuming process if it is to be accomplished with useful spatial resolutions. Spectrum Photonics has developed and demonstrated a prototype system utilizing long wave infrared hyperspectral microscopy, which enables the simultaneous collection of LWIR reflectance spectra from 8-14 μm in a 30 x 7 mm FOV with 30 μm spatial resolution in 30 s. An overview of the uncooled Sagnac-based LWIR HSM system will be given, emphasizing the benefits of this approach. Laboratory Hyperspectral data collected from custom mixtures and fingerprint residues is shown, focusing on the ability of the LWIR chemical micro-imager to detect chemicals of interest out of a cluttered background.

Fourier transform spectroscopy is a widely employed method for obtaining visible and infrared spectral imagery, with applications ranging from the desktop to remote sensing. Most fielded Fourier transform spectrometers (FTS) employ the Michelson interferometer and measure the spectrum encoded in a time-varying signal imposed by the source spectrum interaction with the interferometer. A second, less widely used form of FTS is the spatial FTS, where the spectrum is encoded in a pattern sampled by a detector array. Recently we described using a Fabry-Perot interferometer, with a deliberately wedged gap geometry and engineered surface reflectivities, to produce an imaging spatial FTS. The Fabry-Perot interferometer can be much lighter and more compact than a conventional interferometer configuration, thereby making them suitable for portable and handheld applications. This approach is suitable for use over many spectral regimes of interest, including visible and infrared regions. Primary efforts to date have focused on development and demonstration of long wave infrared (LWIR) spectral imagers. The LWIR version of the miniaturized Fabry-Perot has been shown to be effective for various applications including spectral imaging-based chemical detection. The compact LWIR spectral imager employs uncooled optics and a microbolometer camera; a handheld version is envisioned for future development. Recent advancements associated with the spatial Fourier Transform imaging spectrometer system are described.

Rapidly programmable spatial light modulation devices based on MEMS technology have opened an exciting new arena in spectral imaging: rapidly reprogrammable, high spectral resolution, multi-band spectral filters that enable hyperspectral processing directly in the optical hardware of an imaging sensor. Implemented as a multiplexing spectral selector, a digital micro-mirror device (DMD) can independently choose or reject dozens or hundreds of spectral bands and present them simultaneously to an imaging sensor, forming a complete 2D image. The result is a high-speed, highresolution, programmable spectral filter that gives the user complete control over the spectral content of the image formed at the sensor. This technology enables a wide variety of rapidly reprogrammable operational capabilities within the same sensor including broadband, color, false color, multispectral, hyperspectral and target specific, matched filter imaging. Of particular interest is the ability to implement target-specific hyperspectral matched filters directly into the optical train of the sensor, producing an image highlighting a target within a spectrally cluttered scene in real time without further processing. By performing the hyperspectral image processing at the sensor, such a system can operate with high performance, greatly reduced data volume, and at a fraction of the cost of traditional push broom hyperspectral instruments. Examples of color, false color and target-specific matched-filter images recorded with our visible-spectrum prototype will be displayed, and extensions to other spectral regions will be discussed.