Presented is a new hyperspectral imager design based on multiple slit scanning. This represents an innovation in the classic trade-off between speed and resolution. This LWIR design has been able to produce data-cubes at 3 times the rate of conventional single slit scan devices. The instrument has a built-in radiometric and spectral calibrator.
There is a need for a Precision Radiometric Surface Temperature (PRST) measurement capability that can achieve noncontact profiling of a sample’s surface temperature when heated dynamically during laser processing, aerothermal heating or metal cutting/machining. Target surface temperature maps within and near the heated spot provide critical quantitative diagnostic data for laser-target coupling effectiveness and laser damage assessment. In the case of metal cutting, this type of measurement provides information on plastic deformation in the primary shear zone where the cutting tool is in contact with the workpiece. The challenge in these cases is to measure the temperature of a target while its surface’s temperature and emissivity are changing rapidly and with incomplete knowledge of how the emissivity and surface texture (scattering) changes with temperature. Bodkin Design and Engineering, LLC (BDandE), with partners Spectral Sciences, Inc. (SSI) and Space Computer Corporation (SCC), has developed a PRST Sensor that is based on a hyperspectral MWIR imager spanning the wavelength range 2-5 μm and providing a hyperspectral datacube of 20-24 wavelengths at 60 Hz frame rate or faster. This imager is integrated with software and algorithms to extract surface temperature from radiometric measurements over the range from ambient to 2000K with a precision of 20K, even without a priori knowledge of the target’s emissivity and even as the target emissivity may be changing with time and temperature. In this paper, we will present a description of the PRST system as well as laser heating test results which show the PRST system mapping target surface temperatures in the range 600-2600K on a variety of materials.
Hyperspectral imaging has important benefits in remote sensing and target discrimination applications. This paper
describes a class of snapshot-mode hyperspectral imaging systems which utilize a unique optical processor that provides
video-rate hyperspectral datacubes. This system consists of numerous parallel optical paths which collect the full threedimensional
(two spatial, one spectral) hyperspectral datacube with each video frame and are ideal for recording data
from transient events, or on unstable platforms.
We will present the results of laboratory and field-tests for several of these imagers operating at visible, near-infrared,
MWIR and LWIR wavelengths. Measurement results for nitrate detection and identification as well as additional
chemical identification and analysis will be presented.
Hyperspectral imaging has important benefits in remote sensing and material identification.
This paper describes a class of hyperspectral imaging systems which utilize a novel optical
processor that provides video-rate hyperspectral datacubes. These systems have no moving
parts and do not operate by scanning in either the spatial or spectral dimension. They are
capable of recording a full three-dimensional (two spatial, one spectral) hyperspectral datacube
with each video frame, ideal for recording data on transient events, or from unstabilized
platforms. We will present the results of laboratory and field-tests for several of these imagers
operating in the visible, near-infrared, mid-wavelength infrared (MWIR) and long-wavelength
infrared (LWIR) regions.
There is a strong desire to create narrowband infrared light sources as personnel beacons for application in infrared
Identify Friend or Foe (IFF) systems. This demand has augmented dramatically in recent years with the reports of
friendly fire casualties in Afghanistan and Iraq. ICx Photonics' photonic crystal enhancedTM (PCETM) infrared emitter
technology affords the possibility of creating narrowband IR light sources tuned to specific IR wavebands (near 1-2
microns, mid 3-5 microns, and long 8-12 microns) making it the ideal solution for infrared IFF. This technology is
based on a metal coated 2D photonic crystal of air holes in a silicon substrate. Upon thermal excitation the photonic
crystal modifies the emitted yielding narrowband IR light with center wavelength commensurate with the periodicity of
the lattice. We have integrated this technology with microhotplate MEMS devices to yield 15mW IR light sources in the
3-5 micron waveband with wall plug efficiencies in excess of 10%, 2 orders of magnitude more efficient that
conventional IR LEDs. We have further extended this technology into the LWIR with a light source that produces 9
mW of 8-12 micron light at an efficiency of 8%. Viewing distances >500 meters were observed with fielded camera
technologies, ideal for ground to ground troop identification. When grouped into an emitter panel, the viewing distances
were extended to 5 miles, ideal for ground to air identification.
A compact, low-cost, multi-wavelength NDIR sensor was designed to measure G-type CW agents at ppm-levels. This 4-color sensor can distinguish between the different agents (sarin, soman, tabun) and is more sensitive than a single wavelength sensor. The design of the sensor and test results with simulants R-12 (dichlorodifluoromethane) and sulfur hexafluoride is presented. These test results support a lower detection limit of 3 ppmv for a 1 sec integration time. Modifications of the sensor design which will enable us to achieve <1 ppmv sensitivity are discussed.
Sensors of trace gases are of enormous importance to diverse fields such as environmental protection, household safety, homeland security, bio-hazardous material identification, meteorology and industrial environments. The gases of interest include CO for home environments, CO2 for industrial and environment applications and toxic effluents such as SO2, CH4, NO for various manufacturing environments. We propose a new class of IR gas sensors, where the enabling technology is a spectrally tuned metallo-dielectric photonic crystal. Building both the emitting and sensing capabilities on to a single discrete element, Ion Optics’ infrared sensorchip brings together a new sensor paradigm to vital commercial applications. Our design exploits Si-based suspended micro-bridge structures fabricated using conventional photolithographic processes. Spectral tuning, control of bandwidth and direction of emission were accomplished by specially designed metallo-dielectric photonic crystal surfaces.
Inexpensive optical MEMS gas and chemical sensors offer chip-level solutions to environmental monitoring, industrial health and safety, indoor air quality, and automobile exhaust emissions monitoring. Previously, Ion Optics, Inc. reported on a new design concept exploiting Si-based suspended micro-bridge structures. The devices are fabricated using conventional CMOS compatible processes. The use of photonic bandgap (PBG) crystals enables narrow band IR emission for high chemical selectivity and sensitivity. Spectral tuning was accomplished by controlling symmetry and lattice spacing of the PBG structures. IR spectroscopic studies were used to characterize transmission, absorption and emission spectra in the 2 to 20 micrometers wavelength range. Prototype designs explored suspension architectures and filament geometries. Device characterization studies measured drive and emission power, temperature uniformity, and black body detectivity. Gas detection was achieved using non-dispersive infrared (NDIR) spectroscopic techniques, whereby target gas species were determined from comparison to referenced spectra. A sensor system employing the emitter/detector sensor-chip with gas cell and reflective optics is demonstrated and CO2 gas sensitivity limits are reported.
A new IR-based sensor technology is introduced for environmental monitoring of industrial pollutants (CO2, CO, NOx, etc.). The design concept exploits Si-based, thermally isolated suspended bridge structures. These devices, which function as both IR emitter and detector, are fabricated using MEMS-based processing methods. Photonic bandgap (PBG) modified surfaces enable narrow band IR emission for high chemical selectivity and sensitivity. Spectral tuning is accomplished by controlling symmetry and lattice spacing of the PBG structures. IR spectroscopic studies were used to characterize transmission, absorption and emission spectra in the 2 to 20 micrometers wavelength range. Device characterization studies measured drive and emission power, temperature uniformity, and black body detectivity. Gas detection was achieved using non-dispersive infrared (NDIR) spectroscopic techniques, whereby target gas species and concentrations were determined from comparison to referenced spectra. A sensor system employing the emitter/detector sensor-chip with gas cell and reflective optics is demonstrated and CO2 gas sensitivity limits are reported. A multi-channel microsensor-array is proposed for multigas (e.g., CO2, CO, and NOx, etc.) detection.
MEMS silicon (Si) micro-bridge elements, with photonic band gap (PBG) modified surfaces are exploited for narrow-band spectral tuning in the infrared wavelength regime. Thermally isolated, uniformly heated single crystal Si micro-heaters would otherwise provide gray-body emission, in accordance with Planck's distribution function. The introduction of an artificial dielectric periodicity in the Si, with a surface, vapor-deposited gold (Au) metal film, governs the photonic frequency spectrum of permitted propagation, which then couples with surface plasmon states at the metal surface. Narrow band spectral tuning was accomplished through control of symmetry and lattice spacing of the PBG patterns. Transfer matrix calculations were used to model the frequency dependence of reflectance for several lattice spacings. Theoretical predictions that showed narrow-band reflectance at relevant wavelengths for gas sensing and detection were then compared to measured reflectance spectra from processed devices. Narrow band infrared emission was confirmed on both conductively heated and electrically driven devices.
A NDIR-based sensor-chip using MEMS Si micro-bridge elements, with integrated PBG structure for wavelength tuning is discussed. The effects of processing on device performance, especially device release, were investigated. Thermal and electrical device characterization was used to quantify loss mechanisms. Thermally isolated, uniformly heated emitters were ultimately achieved using a backside release etch fabrication process. The fully released devices demonstrated superior electric to thermal (optical) conversion, with the requisite narrow band emission for CO2 detection. Using the MEMS sensor-chips, 20% CO2 detection was demonstrated, with projected sensitivities of ~3% CO2.
Gas and chemical sensors are used in many applications. Industrial health and safety monitors allow companies to meet OSHA requirements by detecting harmful levels of toxic or combustible gases. Vehicle emissions are tested during annual inspections. Blood alcohol breathalizers are used by law enforcement. Refrigerant leak detection ensures that the Earth's ozone layer is not being compromised. Industrial combustion emissions are also monitored to minimize pollution. Heating and ventilation systems watch for high levels of carbon dioxide (CO2) to trigger an increase in fresh air exchange. Carbon monoxide detectors are used in homes to prevent poisoning from poor combustion ventilation. Anesthesia gases are monitored during a patients operation. The current economic reality is that two groups of gas sensor technologies are competing in two distinct existing market segments - affordable (less reliable) chemical reaction sensors for consumer markets and reliable (expensive) infrared (IR) spectroscopic sensors for industrial, laboratory, and medical instrumentation markets. Presently high volume mass-market applications are limited to CO detectros and on-board automotive emissions sensors. Due to reliability problems with electrochemical sensor-based CO detectors there is a hesitancy to apply these sensors in other high volume applications. Applications such as: natural gas leak detection, non-invasive blood glucose monitoring, home indoor air quality, personal/portable air quality monitors, home fire/burnt cooking detector, and home food spoilage detectors need a sensor that is a small, efficient, accurate, sensitive, reliable, and inexpensive. Connecting an array of these next generation gas sensors to wireless networks that are starting to proliferate today creates many other applications. Asthmatics could preview the air quality of their destinations as they venture out into the day. HVAC systems could determine if fresh air intake was actually better than the air in the house. Internet grocery delivery services could check for spoiled foods in their clients' refrigerators. City emissions regulators could monitor the various emissions sources throughout the area from their desk to predict how many pollution vouchers they will need to trade in the next week. We describe a new component architecture for mass-market sensors based on silicon microelectromechanical systems (MEMS) technology. MEMS are micrometer-scale devices that can be fabricated as discrete devices or large arrays, using the technology of integrated circuit manufacturing. These new photonic bandgap and MEMS fabricataion technologies will simplify the component technology to provide high-quality gas and chemical sensors at consumer prices.
Thermal emission from heated materials follows the blackbody curve, multiplied by emissivity. Emissivity may be, but is not usually a strong function of wavelength. Ion Optics has developed a variety of surface texturing processes that create specific nano-structures which alter the emissivity in predictable fashion. Random structures produced by ion beam etching create long and/or short wavelength cutoffs. Repeated patterns produced by fine-line lithography, resembling photonic bandgap materials, have large peaks in the emitted spectrum. The central wavelength and bandwidth for lithographic structures can be varied with geometry. FWHM values for ((Delta) (lambda) /(lambda) ) are less than 0.1. These light sources reduce power requirements for applications now using broadband sources with filters, and in some cases entirely eliminate the need for filters.
We have developed and demonstrated a reflection-mode optical fiber-based instrument for in situ monitoring and feedback control of thin film dielectric deposition processes. The instrument operates in single-wavelength or multi-wavelength mode. One end of the fiber is placed in the deposition zone, close to the samples being coated. Single or multi-wavelength light is sent down the fiber and the reflected light from the end being coated is analyzed for intensity vs. wavelength. The fiber end being coated features an easily replaced tip to prevent loss of resolution when the coating becomes too thick. For processes in which the index of refraction or composition of the thin films is fixed, the less expensive single wavelength instrument is sufficient and measures thickness of the films by counting interference fringes. For processes in which film composition or index of refraction are variable, we use a white light source and compact spectrograph to measure reflectance vs. wavelength. For critical applications like diode laser facet coating where yield loss is significant cost driver, this monitor measures the thickness and index of refraction of single and multi-layer thin films as they are deposited. More importantly, it measures the critical parameter of interest: reflectance at the actual laser emission wavelength. This instrument replaces quartz crystal oscillators and other, more complex instruments.
IR sensing has been a key enabling technology in military systems providing advantages in night vision, surveillance, and ever more accurate targeting. Passive hyperspectral imagin, the ability to gather and process IR spectral information from each pixel of an IR image, can ultimately provide 2D composition maps of a scene under study. FInding applications such as atmospheric, and geophysical remote sensing, camouflaged target recognition, and defence against chemical weapons.
In the past ten years, a number of miniature spectrometers covering the visible and near infrared wavelengths out to 2.5 microns wavelength have been developed and are now commercially available. These small but high performance instruments have taken advantage of continuing advances in high sensitivity detectors--both CCD's and diode arrays, improvements in holographic gratings, and the availability of low-loss optical materials both in bulk and fiber form that transmit at these wavelengths and that can readily be formed into monolithic shapes for complex optical structures. More recently, a number of researchers have addressed the more intractable problems of extending these miniaturization innovations to spectrometers capable of operation in the mid-infrared wavelengths from 3 microns to 12 microns and beyond. Key enabling technologies for this effort include the recent development of high D*, uncooled thermopile and micro-bolometer detector arrays, new low- mass, high-efficiency pulsed infrared sources, and the design and fabrication of novel monolithic optical structures and waveguides using high index infrared optical materials. This paper reviews the development of these innovative infrared spectrometers and, in particular, the development of the `wedge' spectrometer by Foster-Miller, Inc. and the MicroSpecTM, a MEMS-based solid state spectrograph, by Ion Optics, Inc.
This paper reports the deposition of (100) GaAs and (111)B CdZnTe layers on silicon substrates up to 4-inch diameter to produce substrates suitable for liquid phase epitaxy (LPE) of high-quality HgCdTe layers. Metalorganic chemical vapor deposition is used for both GaAs and CdZnTe in a reactor capable of deposition onto eighteen 3-inch or ten 4-inch wafers per run. An encapsulation scheme is described that prevents contamination of a Te melt by Si or GaAs during LPE growth. Excellent uniformity of thickness and Zn concentration are achieved in the MOCVD films. The CdZnTe films show only lamellar twins close to the GaAs interface; no twins capable of propagating into the HgCdTe layer are formed. These substrates have been used for the growth of pure HgCdTe films having a dislocation density that is only a factor of 2 to 4 higher than that measured in similar films grown on bulk CdTe substrates.