Proceedings Volume 7319

Next-Generation Spectroscopic Technologies II

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Proceedings Volume 7319

Next-Generation Spectroscopic Technologies II

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Volume Details

Date Published: 28 April 2009
Contents: 4 Sessions, 18 Papers, 0 Presentations
Conference: SPIE Defense, Security, and Sensing 2009
Volume Number: 7319

Table of Contents

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Table of Contents

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  • Front Matter: Volume 7319
  • Imaging Spectroscopy
  • Miniature and Portable Spectrometers
  • MEMS-based Spectrometers
Front Matter: Volume 7319
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Front Matter: Volume 7319
is PDF file contains the front matter associated with SPIE Proceedings Volume 7319, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.
Imaging Spectroscopy
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Molecular imaging by confocal Raman mapping: enabling technologies for speed, multivariate analysis, and convenience
In spite of the fact that the original Raman microscope was designed in the early 1970's for Raman imaging, wide-spread practical use of the technology did not appear until the last 5 years. The instruments are smaller, faster, easier-to-use, promoting reports of a variety of interesting applications in fields as diverse as nanomaterials, pharmaceuticals, composites, semiconductors, bio-clinical studies, polymers, ceramics and glasses. While the information content in Raman analysis is quite high, the time to acquire an image has been a deterrent to its application. Recent innovations including Swift and DUO Scan have addressed and are addressing these issues. SWIFT (Scanning with Incredibly Fast Times) is a rapid CCD read-out technique that is based on the synchronization between the XY motion of the motorized or piezo stage and the CCD readout. DUO scanning uses a set of scanning mirrors above the microscope objective to raster rapidly the laser beam across a sample area. This can be used to create a "giant pixel" in the map without compromising the NA of the light collection, or to create a map with step sizes as small as 10nm. Swift, in combination with DUO scan, as been used to produce full spectral maps of pharmaceutical tablets in times as short as 10 minutes, something that was previously believed to be near impossible. Off-line analysis of such a map using multivariate techniques produces Raman images indicating the quality of component mixing, and also the presence of minor, difficult-to-detect components (such as Mgstearate in pharmaceutical tablets).
Characterization of spatial and spectral resolution of a rotating prism chromotomographic hyperspectral imager
Randall L. Bostick, Glen P. Perram, Ronald Tuttle
The Air Force Institute of Technology (AFIT) has built a rotating prism chromotomographic hyperspectral imager (CTI) with the goal of extending the technology to exploit spatially extended sources with quickly varying (> 10 Hz) phenomenology, such as bomb detonations and muzzle flashes. This technology collects successive frames of 2-D data dispersed at different angles multiplexing spatial and spectral information which can then be used to reconstruct any arbitrary spectral plane(s). In this paper, the design of the AFIT instrument is described and then tested against a spectral target with near point source spatial characteristics to measure spectral and spatial resolution. It will be shown that, in theory, the spectral and spatial resolution in the 3-D spectral image cube is the nearly the same as a simple prism spectrograph with the same design. However, error in the knowledge of the prism linear dispersion at the detector array as a function of wavelength and projection angle will degrade resolution without further corrections. With minimal correction for error and use of a simple shift-and-add reconstruction algorithm, the CTI is able to produce a spatial resolution of about 2 mm in the object plane (234 μrad IFOV) and is limited by chromatic aberration. A spectral resolution of less than 1nm at shorter wavelengths is shown, limited primarily by prism dispersion.
Rapid calibrated high-resolution hyperspectral imaging using tunable laser source
We present a novel hyperspectral imaging technique based on tunable laser technology. By replacing the broadband source and tunable filters of a typical NIR imaging instrument, several advantages are realized, including: high spectral resolution, highly variable field-of-views, fast scan-rates, high signal-to-noise ratio, and the ability to use optical fiber for efficient and flexible sample illumination. With this technique, high-resolution, calibrated hyperspectral images over the NIR range can be acquired in seconds. The performance of system features will be demonstrated on two example applications: detecting melamine contamination in wheat gluten and separating bovine protein from wheat protein in cattle feed.
Applications of spectral imaging using a tunable laser source
David C. Oertel, Jeffrey T. Grothaus, Curtis Marcott
Hyperspectral reflectance imaging in the visible and NIR spectral ranges has considerable utility for revealing spatial and chemical complexity in both biological systems and manufactured products. Conventional imaging systems are based on broad-band illumination in tandem with a spectrometer or tunable filter placed between the sample and the detector. These systems are typically slow (require seconds of integration per wavelength step), and the CW broad-band source can cause significant heating of the sample. An alternative method is to use a tunable, pulsed, high-peak-power (low average power) source coupled with a broad-band detector. This approach offers a reduction in data acquisition time, the inherent ability to stop motion, and data collection at ambient temperature. An integrated system based on a 5- ns pulsed laser tunable from 430 nm to 2150 nm has been used to obtain hyperspectral images in both the visible and NIR spectral ranges. A number of camera/lens options allow for varied spectral bandwidths and the FOV, ranging from 11 × 15 mm2 to 15 × 20 cm2. An entire hyperspectral image stack can be collected in as little as 20 s. This method, allowing fast, room-temperature data acquisition, has sufficient sensitivity to produce data that can be successfully processed using spectral derivatives and multivariate analysis. We discuss several applications, both in vivo and otherwise, of this alternative approach to visible/NIR hyperspectral imaging.
Advanced pushbroom hyperspectral LWIR imagers
Performance studies and instrument designs for hyperspectral pushbroom imagers in thermal wavelength region are introduced. The studies involve imaging systems based on both MCT and microbolometer detector. All the systems employ pushbroom imaging spectrograph with transmission grating and on-axis optics. The aim of the work was to design high performance instruments with good image quality and compact size for various application requirements. A big challenge in realizing these goals without considerable cooling of the whole instrument is to control the instrument radiation from all the surfaces of the instrument itself. This challenge is even bigger in hyperspectral instruments, where the optical power from the target is spread spectrally over tens of pixels, but the instrument radiation is not dispersed. Without any suppression, the instrument radiation can overwhelm the radiation from the target by 1000 times. In the first imager design, BMC-technique (background monitoring on-chip), background suppression and temperature stabilization have been combined with cryo-cooled MCT-detector. The performance of a very compact hyperspectral imager with 84 spectral bands and 384 spatial samples has been studied and NESR of 18 mW/(m2srμm) at 10 μm wavelength for 300 K target has been achieved. This leads to SNR of 580. These results are based on a simulation model. The second version of the imager with an uncooled microbolometer detector and optics in ambient temperature aims at imaging targets at higher temperatures or with illumination. Heater rods with ellipsoidal reflectors can be used to illuminate the swath line of the hyperspectral imager on a target or sample, like drill core in mineralogical analysis. Performance characteristics for microbolometer version have been experimentally verified.
Performance and applications of a hypertemporal hyperspectral Fourier-transform infrared spectroradiometer
Bruce H. King, Thomas Ellis, Tom E. Old
A fast-scanning, high-resolution FTIR spectroradiometer has been designed and built for use in remote sensing, stand-off detection, and spectral-temporal characterization of fast, energetic infrared events. The instrument design uses a Michelson-type interferometer with a rotary modulator which is capable of continuous measurement of infrared spectra at a rate of 1000 scans per second with 4 cm-1 resolution in the 2 - 25 micron spectral range. Sensitivity, spectral accuracy, and radiometric precision are discussed along with specific design parameters. This instrument can be used for passive sensing as a stand-alone sensor, or for active sensing as a receiver when used in conjunction with a highenergy excitation source such as a laser. Applications include muzzle flash signature measurement, ordnance detonation characterization, missile plume identification, and rocket motor combustion diagnostics.
Novel hyperspectral prediction method and apparatus
Gabor J. Kemeny, Natalie A. Crothers, Gard A. Groth, et al.
Both the power and the challenge of hyperspectral technologies is the very large amount of data produced by spectral cameras. While off-line methodologies allow the collection of gigabytes of data, extended data analysis sessions are required to convert the data into useful information. In contrast, real-time monitoring, such as on-line process control, requires that compression of spectral data and analysis occur at a sustained full camera data rate. Efficient, high-speed practical methods for calibration and prediction are therefore sought to optimize the value of hyperspectral imaging. A novel method of matched filtering known as science based multivariate calibration (SBC) was developed for hyperspectral calibration. Classical (MLR) and inverse (PLS, PCR) methods are combined by spectroscopically measuring the spectral "signal" and by statistically estimating the spectral "noise." The accuracy of the inverse model is thus combined with the easy interpretability of the classical model. The SBC method is optimized for hyperspectral data in the Hyper-CalTM software used for the present work. The prediction algorithms can then be downloaded into a dedicated FPGA based High-Speed Prediction EngineTM module. Spectral pretreatments and calibration coefficients are stored on interchangeable SD memory cards, and predicted compositions are produced on a USB interface at real-time camera output rates. Applications include minerals, pharmaceuticals, food processing and remote sensing.
Miniature and Portable Spectrometers
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Adaptive spectroscopy for rapid chemical identification
Dineshbabu V. Dinakarababu, Michael E. Gehm
Spectroscopic chemical identification is fundamentally a classification task where sensor measurements are compared to a library of known compounds with the hope of determining an unambiguous match. When the measurement signal-to-noise ratio (SNR) is very low (e.g. from short exposure times, weak analyte signatures, etc.), classification can become very challenging, requiring a multiple-measurement framework such as sequential hypothesis testing, and dramatically extending the time required to classify the sample. There are a wide variety of defense, security, and medical applications where rapid identification is essential, and hence such delays are disastrous. In this paper, we discuss an approach for adaptive spectroscopic detection where the introduction of a tunable spectral filter enables the system to measure the projection of the sample spectrum along arbitrary bases in the spectral domain. The net effect is a significant reduction in time-to-decision in low SNR cases. We describe the general operation of such an instrument, present results from initial simulations, and report on our experimental progress.
Portable Raman instrument for rapid biological agent detection and identification
Marie L. Lesaicherre, Tracy L. Paxon, Frank J. Mondello, et al.
The rapid and sensitive identification of biological species is a critical need for the 1st responder and military communities. Raman spectroscopy is a powerful tool for substance identification that has gained popularity with the respective communities due to the increasing availability of portable Raman spectrometers. Attempts to use Raman spectroscopy for the direct identification of biological pathogens has been hindered by the complexity of the generated Raman spectrum. We report here the use of a sandwich immunoassay containing antibody modified magnetic beads to capture and concentrate target analytes in solution and Surface Enhanced Raman Spectroscopy (SERS) tags conjugated with these same antibodies for specific detection. Using this approach, the biological complexity of a microorganism can be translated into chemical simplicity and Raman can be used for the identification of biological pathogens. The developed assay has a low limit of detection due to the SERS effect, robust to commonly found white powders interferants, and stable at room temperature over extended period of time. This assay is being implemented into a user-friendly interface to be used in conjunction with the GE Homeland Protection StreetLab MobileTM Raman instrument for rapid, field deployable chemical and biological identification.
Coded-aperture DUV spectrometer for stand-off Raman spectroscopy
We have designed and constructed a coded aperture spectrometer for use in the deep UV range. The Czerny-Turner design provides sufficient spectral resolution to observe Raman scattering features, while the use of a coded aperture provides a greatly improved light collection efficiency for scattering sources. The resulting instrument is capable of analyzing Raman spectra from samples at a 1 meter viewing distance. We provide an overview of the system, its optical design, and some preliminary measurements.
Advances in portable FTIR spectrometers for the field: the HazMatID Ranger
Recent advances in the design of compact interferometers and infrared sampling accessories have allowed FTIR spectroscopy to be taken out of the laboratory and into the field. The chemical identification capability of mid-infrared spectroscopy has filled many needs of military, security, and emergency response personnel. Further design optimization has led to the development of a hand-held FTIR system, the HazmatID Ranger, which enables new applications in chemical identification and offers increased flexibility for elusive samples encountered in the field. An overview of the performance of the HazmatID Ranger using a receiver operating characteristic analysis is presented along with a discussion of the viability of hand-held FTIR measurements for applications in defense and security.
MEMS-based Spectrometers
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Recent advances in compact broadly tunable external-cavity quantum cascade lasers (ECqcL)
Timothy Day, Miles Weida, David Arnone, et al.
Recent advances in commercially available quantum cascade semiconductor materials providing laser gain in the 3- 12μm regime have been developed. This enables wavelength tunable, narrow linewidth external cavity quantum cascade laser (ECqcL) sources operating above room temperature to be realized with high yield. Daylight has combined these materials with advanced coating and attach technologies, mid-IR micro-optics and telecom-style packaging to yield compact, hermetically-sealed lasers. In addition, ultra-broad tuning ranges (>250 wavenumbers) have been demonstrated from a commercially available product platform. Meanwhile, phase continuous tuning capabilities have been achieved to provide the ability to perform wavelength modulation spectroscopy in the mid-IR from similar commercial platforms. When integrated and optimized with new room temperature mid-IR detectors and modern low power embedded digital signal processing electronics, the resulting sensor platform can provide significant advantages. These include multispecies fingerprint identification at real-time update rates (10 Hz). Daylight will review the most recent progress in ECqcL devices as well as describe their portable, battery-operated Swept SensorTM technology based upon this platform.
Diffractive MEMS components, systems, and applications
A MEMS (micro electro mechanical system) technology has been used to produce scanning grating chips which have a tiltable plate with grating structures optimized for the 900nm ... 2500nm range as diffractive element. Based on these chips different spectrometers and a hyper spectral imager have been realized for NIR-spectroscopic applications like agricultural quality analysis, recycling and process control. Ongoing developments aim at the further reduction of size and effort. Chip scale or wafer scale packaging technologies could help to shrink the complete spectroscopic system. The integration of signal processing and evaluation routines opens new applications for a broad range of scientific and nonscientific users.
Large stroke MOEMS actuators for optical path length modulation in miniaturized FTIR spectrometers
In this paper we present a novel translatory MOEMS device with extraordinary large stroke especially designed for fast optical path modulation in an improved miniaturized Fourier-transform infrared (FTIR) spectrometer capable to perform time resolved measurements from NIR to MIR. Recently, we presented a first MOEMS based FTIR system using a different translatory MOEMS actuator with bending suspensions of the mirror plate and ±100μm oscillation amplitude resulting in a limited spectral resolution of 30 cm-1. For the novel MOEMS actuator an advanced pantograph suspension of the mirror plate was used to guarantee an extraordinary large stroke of up to 500 μm required for an improved spectral resolution. To optimize the optical throughput of the spectrometer the mirror aperture was increased to 7 mm2. The MOEMS actuators are driven electro statically resonant using out-of-plane comb drives and operate at a resonant frequency of 500 (1000) Hz, respectively. Hence, this enables to realize an improved MOEMS based FTIR-spectrometer with a spectral resolution of up to 10 cm-1, a SNR of > 1000:1 and an acquisition time of 1 ms per spectrum of the miniaturized FTIR-system. In this article we discuss in detail the design and the experimental characteristics of the novel large stroke translatory MOEMS device. The application and system integration, especially the optical vacuum packaging, of this MOEMS device in an improved miniaturized MOEMS based FTIR spectrometer enabling ultra rapid measurements in the NIRMIR spectral region with 12cm-1 spectral resolution is discussed in a separate paper submitted to this conference.
Improved MOEMS-based ultra-rapid Fourier transform infrared spectrometer
A. Tortschanoff, A. Kenda, M. Kraft, et al.
We present an improved FTIR spectrometer using a novel MOEMS actuator and discuss in detail the properties of the MOEMS component and the resulting FT-IR sensor device. Spectral resolution and the spectral range allow making use of the inherent multi-analyte detection capabilities giving the spectroscopy platform an advantage over singlewavelength IR sensors. With its further miniaturization potential due to its MOEMS core, this compact, energy efficient and robust spectrometer can thus act as transducer for portable and ultra-lightweight spectroscopic IR sensors, e.g. all purpose hazardous vapor sensors, sensors for spaceborne and Micro-UAV based IR analysis, and many more.
High-resolution miniature FTIR spectrometer enabled by a large linear travel MEMS pop-up mirror
Erik R. Deutsch, David Reyes, Elliot R Schildkraut, et al.
This paper reports the design, fabrication, and characterization of a millimeter diameter, surface micromachined Micro-Electro-Mechanical-Systems (MEMS) mirror, which is assembled perpendicular to the substrate and can be linearly and repeatedly traversed through 600 μm. The moving mirror, when combined with a fixed mirror and beamsplitter, make up a monolithic MEMS Michelson interferometer; all are made on the same substrate and in the same surface micromachined fabrication process. The beamsplitter has been specifically designed such that the motion of the mirror enables modulation of light over the 2-14 μm spectral region. The rapid scan MEMS Michelson interferometer is the engine behind a miniaturized, Fourier transform infrared (FTIR) absorption spectrometer. The FTIR measures the absorption of infrared (IR) radiation by a target material, which can be used for the detection and identification of gases, liquids, or solids. The fabrication of the mirror with the ability to displace 600 μm along the optical axis enables the miniaturized system to have species identification resolution, while leveraging wafer scale batch fabrication to enable extremely low system cost. The successful fabrication of the millimeter diameter mirrors and beamsplitter with interferometric alignment over the range of travel of the moving mirror promises unprecedented sensitivity relative to the size of the FTIR spectrometer system.
MEMS-based Fabry-Perot microspectrometers for agriculture
This paper reports work on the development of rugged micro-electromechanical systems (MEMS)-based microspectrometers for real-time applications in agriculture. The devices are electrostatically actuated, first order Fabry- Perot tuneable optical filters, hybridised with InGaAs photodiode detectors. Tuning range and resolution of the devices are 1615 nm to 2425 nm and 52 nm (FWHM) at 2000 nm, respectively. To our knowledge, this tuning range is the largest reported for a MEMS-based Fabry-Perot filter. Three-layer distributed Bragg reflectors are used for the Fabry- Perot mirrors, and consist of e-beam evaporated layers of germanium - silicon monoxide - germanium. The moveable mirror also includes two silicon nitride layers that act as the MEMS flexures, stress compensation layers, and as an encapsulant for the mirror layers. The spectral resolution matches the theoretical expected for the mirror structures used when the residual bowing of the mirror (~15 nm across a diameter of 70 μm) is included, and can be improved to ~10 nm if five layer mirrors are used. The out of band rejection is approximately 20 dB. Experimental results show that the throughput of the device is sufficient to allow transmittance, specular reflectance and diffuse reflectance spectra to be measured. The primary outstanding issue is wavelength calibration, and is being addressed using a number of approaches including incorporation of wavelength calibration standards in the hybrid structure and accurate, real-time measurement of the separation of the two mirrors.