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.
Field test results are presented for a prototype long-wave adaptive imager that provides both hyperspectral imagery and contrast imagery based on the direct application of hyperspectral detection algorithms in hardware. Programmable spatial light modulators are used to provide both spectral and spatial resolution using a single element detector. Programmable spectral and spatial detection filters can be used to superimpose any possible analog spectral detection filter on the image. In this work, we demonstrate three modes of operation, including hyperspectral imagery, and one and two-dimensional imagery using a generalized matched filter for detection of a specific target gas within the scene.
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.
The quick atmospheric correction (QUAC) code performs atmospheric correction on multi- and hyperspectral imagery spanning all or part of the visible and near infrared-short wave infrared spectral range, ∼ 400−2500 nm. It utilizes an in-scene approach, requiring only approximate specification of sensor band locations (i.e., central wavelengths) and their radiometric calibration; no additional metadata is required. Because QUAC does not involve first principles radiative-transfer calculations, it is significantly faster than physics-based methods; however, it is also more approximate. We present a detailed description of the QUAC algorithm, highlighting recent accuracy improvements. Example results for several multi-and hyperspectral data sets are presented, and comparisons are made to more rigorous correction approaches.
Proc. SPIE. 7210, Emerging Digital Micromirror Device Based Systems and Applications
KEYWORDS: Long wavelength infrared, Signal to noise ratio, Optical filters, Detection and tracking algorithms, Imaging systems, Sensors, Interference (communication), Micromirrors, Digital micromirror devices, Electronic filtering
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.