A new, compact and portable spectral imaging camera, employing a MEMs-based encoded imaging approach, has been built and demonstrated for detection of hazardous contaminants including gaseous effluents and solid-liquid residues on surfaces. The camera is called the Thermal infrared Reconfigurable Analysis Camera for Effluents and Residues (TRACER). TRACER operates in the long wave infrared and has the potential to detect a wide variety of materials with characteristic spectral signatures in that region. The 30 lb. camera is tripod mounted and battery powered. A touch screen control panel provides a simple user interface for most operations. The MEMS spatial light modulator is a Texas Instruments Digital Microarray Array with custom electronics and firmware control. Simultaneous 1D-spatial and 1Dspectral dimensions are collected, with the second spatial dimension obtained by scanning the internal spectrometer slit. The sensor can be configured to collect data in several modes including full hyperspectral imagery using Hadamard multiplexing, panchromatic thermal imagery, and chemical-specific contrast imagery, switched with simple user commands. Matched filters and other analog filters can be generated internally on-the-fly and applied in hardware, substantially reducing detection time and improving SNR over HSI software processing, while reducing storage requirements. Results of preliminary instrument evaluation and measurements of flame exhaust are presented.
A quantum cascade laser (QCL) tuning mechanism based on an external laser cavity containing a Micro
ElectroMechanical System (MEMS) spatial light modulator in the form of a two-dimensional digital micromirror array
(DMA) is described. The laser is tuned by modulating the reflectivity of DMA micromirror pixels under computer
control. The resulting functionality enables fast (<0.1ms switching time) digitally controlled random-access wavelength
tuning, high-bandwidth wavelength modulation (~30kHz modulation rate), and stable wavelength locking of the laser
output. With one or more QCL gain elements built into the cavity, it is possible to cover a wide portion of the mid-wave
and/or long-wave spectral range with a single device. The fast wideband digitally controlled laser tuning technology
described is applicable to other tunable laser including solid-state, diode, gas, and fiber lasers.
A second-generation long-wave hyperspectral imager based on micro-electro-mechanical systems (MEMS) technology is in development. Spectral and spatial encoding using a MEMS digital micro-mirror device enables fast, multiplexed data acquisition with arbitrary spectral response functions. The imager may be programmed to acquire spectrally selective contrast imagery, replacing more time-consuming hyperspectral data collection. A single-element detector collects encoded data and embedded real-time hardware generates imagery. An internal scanning mechanism enables rapid retrieval of full hyperspectral imagery. The resulting rugged, low-cost sensor will provide chemically specific imagery for applications in gaseous and surface contaminant detection, surveillance, remote sensing, and process control.
A dispersive transform spectral imager named FAROS (FAst Reconfigurable Optical Sensor) has been developed for
high frame rate, moderate-to-high resolution hyperspectral imaging. A programmable digital micromirror array (DMA)
modulator makes it possible to adjust spectral, temporal and spatial resolution in real time to achieve optimum tradeoff
for dynamic monitoring requirements. The system’s F/2.8 collection optics produces diffraction-limited images in the
mid-wave infrared (MWIR) spectral region. The optical system is based on a proprietary dual-pass Offner configuration
with a single spherical mirror and a confocal spherical diffraction grating. FAROS fulfills two functions simultaneously:
one output produces two-dimensional polychromatic imagery at the full focal plane array (FPA) frame rate for fast object
acquisition and tracking, while the other output operates in parallel and produces variable-resolution spectral images via
Hadamard transform encoding to assist in object discrimination and classification. The current version of the FAROS
spectral imager is a multispectral technology demonstrator that operates in the MWIR with a 320 x 256 pixel InSb FPA
running at 478 frames per second resulting in time resolution of several tens of milliseconds per hypercube. The
instrument has been tested by monitoring small-scale rocket engine firings in outdoor environments. The instrument has
no macro-scale moving parts, and conforms to a robust, small-volume and lightweight package, suitable for integration with
small surveillance vehicles. The technology is also applicable to multispectral/hyperspectral imaging applications in diverse
areas such as atmospheric contamination monitoring, agriculture, process control, and biomedical imaging, and can be
adapted for use in any spectral domain from the ultraviolet (UV) to the LWIR region.
Proc. SPIE. 7210, Emerging Digital Micromirror Device Based Systems and Applications
KEYWORDS: Sensors, Digital micromirror devices, Imaging systems, Optical filters, Electronic filtering, Long wavelength infrared, Micromirrors, Interference (communication), Detection and tracking algorithms, Signal to noise ratio
Dispersive transform spectral imagers with both one- and two-dimensional spatial coverage have been demonstrated and
characterized for applications in remote sensing, target classification and process monitoring. Programmable spatial
light modulators make it possible to adjust spectral, temporal and spatial resolution in real time, as well as implement
detection algorithms directly in the digitally controlled sensor hardware. Operating parameters can be optimized in real
time, in order to capture changing background and target evolution. Preliminary results are presented for short wave,
mid-wave, and long-wave infrared sensors that demonstrate the spatial and spectral versatility and rapid adaptability of
this new sensor technology.
Optical sensors aboard space vehicles designated to perform seeker functions need to generate multispectral images in the mid-wave infrared (MWIR) and long-wave infrared (LWIR) spectral regions in order to investigate and classify man-made space objects, and to distinguish them relative to the interfering scene clutter. The spectral imager part of the sensor collects spectral signatures of the observed objects in order to extract information on surface emissivity and target temperature, both important parameters for object-discrimination algorithms. The Adaptive Spectral Imager described in this paper fulfills two functions simultaneously: one output produces instantaneous two-dimensional polychromatic imagery for object acquisition and tracking, while the other output produces multispectral images for object discrimination and classification. The spectral and temporal resolution of the data produced by the spectral imager are adjustable in real time, making it possible to achieve optimum tradeoff between different sensing functions to match dynamic monitoring requirements during a mission. The system has high optical collection efficiency, with output data rates limited only by the readout speed of the detector array. The instrument has no macro-scale moving parts, and can be built in a robust, small-volume and lightweight package, suitable for integration with space vehicles. The technology is also applicable to multispectral imaging applications in diverse areas such as surveillance, agriculture, process control, and biomedical imaging, and can be adapted for use in any spectral domain from the ultraviolet (UV) to the LWIR region.
The work on the development of compact diode laser-based lidar systems at SRI International is reviewed. Two systems, a pseudorandom modulation lidar, and a mobile remote sensor for natural gas pipeline leak detection are described in detail, and experimental results are presented. Methods to enhance signal detection by digital filtering are also reviewed.
New developments in the semiconductor industry are driven by two trends: reducing the device dimensions and further increase of the switching speeds or electrical bandwidths. The electronics industry average feature sizes of integrated circuits (ICs) will be of the order of 100 nm by the year 2010. For instance, currently produced MOS field-effect transistors support electrical fields between the source and the drain that are greater than 105 V/micrometer with switching speeds of 10 - 100 psec. Techniques which would resolve such electrical fields, with the appropriate resolutions in time and in space, are of paramount interest both at the industrial level and in basic research. Initial experiments performed on samples consisting of two metallic electrodes deposited on fused silica substrates covered by thin polymer films show that with only 1 (mu) W of average optical power, a second harmonic signal triggered by an AC/DC field could easily be detected with a spatial resolution of less than 1 micrometer. We anticipate electrical field detection sensitivity of less than 1 mV/micrometer with our technique with 100 nm resolution spatially and less than 1 psec resolution in time.