OPTRA is currently developing a Risley Prism Universal Pointing System (RPUPS): a highly customizable cued beamsteering system. The RPUPS consists of a visible or infrared cueing imager co-aligned with an optical beam steering system’s pointing-field-of-regard. The cueing imager is used to identify a region-of-interest within its wide field-of-view, via a wireless tablet device. The tablet user can choose to manually or automatically, identify and track regions-of-interest. The optical beam steering system uses a matched pair of Risley Prisms to direct an interrogating optical system’s instantaneous-field-of-view onto the identified region-of-interest. The tablet updates the user with real time information from both the cueing imager and the interrogating optical system. Risley prism material and geometry choices provide operating wavelength, aperture size, and field-of-regard flexibility for this front-end pointing component. Back-end components may be receive-only, transmit-only, or transmit/receive combinations. The flexibility of the RPUPS allows for mission specific customization where applications include but are not limited to: synthetic foveated imaging, spectroscopic probes and laser (LIDAR) ranging and tracking. This paper will focus on the design and anticipated applications of the RPUPS.
The proliferation of lasers has led to their widespread use in applications ranging from short range standoff chemical detection to long range Lidar sensing and target designation operating across the UV to LWIR spectrum. Recent advances in high energy lasers have renewed the development of laser weapons systems. The ability to measure and assess laser source information is important to both identify a potential threat as well as determine safety and nominal hazard zone (NHZ). Laser detection sensors are required that provide high dynamic range, wide spectral coverage, pulsed and continuous wave detection, and large field of view. OPTRA, Inc. and Tufts have developed a custom ROIC smart pixel imaging sensor architecture and wavelength encoding optics for measurement of source wavelength, pulse length, pulse repetition frequency (PRF), irradiance, and angle of arrival. The smart architecture provides dual linear and logarithmic operating modes to provide 8+ orders of signal dynamic range and nanosecond pulse measurement capability that can be hybridized with the appropriate detector array to provide UV through LWIR laser sensing. Recent advances in sputtering techniques provide the capability for post-processing CMOS dies from the foundry and patterning PbS and PbSe photoconductors directly on the chip to create a single monolithic sensor array architecture for measuring sources operating from 0.26 – 5.0 microns, 1 mW/cm2 – 2 kW/cm2.
A number of optical techniques are available to perform active standoff trace explosive detection. Integrating a laser scanner provides the ability to detect explosives over a wide area as well as to assess the full extent of a threat. Risley prism laser-beam steering systems provide a robust alternative to conventional scanner solutions and are ideal for portable and mobile systems due to their compact size, low power, large field-of-view, and fast scan speed. The design of a long-wave infrared Risley prism-scanned diffuse reflectance spectroscopy system along with data obtained from a prototype system is presented for both simulant and live explosive materials.
The authors present a study focused on the feasibility of using holographic polymer dispersed liquid crystal wavelength filters for hyperspectral imaging (HSI). For this study, stacks of these filters were fabricated in the visible wavelength range of 600 to 800 nm. These filters were demonstrated to have a number of properties useful for HSI applications, including uniform reflection efficiency of 80% across a 35 mm optical aperture, polarization insensitivity for normal incidence, spectral resolution of 10 nm, and fast switching times on the order of microseconds. In addition, the ability to modulate each filter in the stack at a different frequency allows for spectral multiplexing, thus enabling synchronous detection and demodulation of the image data. Although the filters in their current state show promise for HSI applications, techniques to further improve performance in terms of viewing angle range and transmission throughput are presented. Finally, a system level integration of such a stack into the prototype drive and detection unit is discussed.
OPTRA is developing a compact, wide field standoff diffuse reflectance spectrometer for trace explosive detection from
a safe standoff. This system is comprised of two key components: a Risley scanner and an infrared tunable laser based
spectrometer. The Risley scanner is a mature technology, which uses a pair of matched prisms to steer a laser beam
anywhere inside a cone. The compact size, low operating power, and large field of view of the Risley scanner make it the
ideal solution for rapidly scanning the laser over the field. The infrared tunable laser spectrometer utilizes a low-cost
quartz crystal tuning fork (QCTF) in place of a traditional infrared detector. The large Q-factor of the QCTF enables
high sensitivity, low noise detection of explosive signatures even for low concentrations and large standoffs. By
coupling this demonstrated technology with a mature Risley scanner design, the field can be scanned both spatially and
spectrally. Pairing this data with sophisticated algorithms results in a map of explosives in the field. This paper presents
OPTRA's breadboard spectrometer design along with the TNT and RDX spectra it produced.
Lasers for defense applications continue to grow in power and fill in new portions of the spectrum, expanding the laser eye safety hazard, particularly to aircrew and aviation safety. The Laser Event Recorder Program within Naval Air Systems Command (NAVAIR) seeks to develop a low cost, self-contained laser sensor able to detect, warn and record laser exposures that hazard aircrew vision. The spectral and temporal range of hazardous lasers (400 to 1600 nm and pulsed to continuous) has presented a challenge in the past. However, diffractive optics and imaging technologies have enabled a solution to this growing threat. This paper will describe the technical requirements for the Laser Event Recorder, which are based on ANSI Z136.1 laser safety standards and common to its use on any platform. To support medical and operational laser eye protection, the LER extracts and records laser wavelength, radiant exposure, exposure duration, pulse structure, latitude, longitude, altitude and time of laser exposure. Specific performance and design issues of the LER prototype will be presented in a companion paper. In this paper, fundamental challenges to the requirements encountered during the first two years of research, development and successful outdoor testing will be reviewed. These include discrimination against all outdoor light levels and the impact of atmospheric beam propagation on accuracy of the radiant exposure determination. Required accuracy and response time of the determination of whether a laser exposure exceeds the maximum permissible exposure (MPE) will be described. Ongoing efforts to coordinate laser exposure reporting and medical management will also be discussed.
The primary objective of this effort is to develop a low-cost, self-powered, and compact laser event recorder and warning sensor for the measurement of laser events. Previously we reported on the technology and design of the Laser Event Recorder. In this paper we describe results from a series of ground and airborne tests of the Laser Event Recorder.
The primary objective of this effort is to develop a low-cost, self-powered, and compact laser event recorder and warning sensor for the measurement of laser events. The target requirements are to measure the wavelength, irradiance, pulse length, pulse repetition frequency, duration and scenery image for each event and save the information in a time and location stamped downloadable file. The sensor design is based on a diffraction grating, low-cost optics, CCD array technology, photodiodes, integral global positioning sensor, and signal processing electronics. The sensor has applications in laser safety, video surveillance and pattern recognition.
KEYWORDS: Raman spectroscopy, Telescopes, Spectroscopy, CRTs, Control systems, Reflector telescopes, Ocean optics, Mirrors, Transformers, Signal to noise ratio
We present our work towards developing a compact reflector telescope (CRT) for short-range (1 to 50 m) standoff Raman LIDAR applications, including a standoff Raman measurement employing our telescope wiht a commercial off the shelf (COTS) laser, spectrometer, and Raman edge filter. This development effort was funded through an SBIR contract from the Department of Energy. The application of this technology is standoff assessment of chemical spills. The CRT system includes a small Galilean telescope to deliver the excitation beam to the surface under investigation; the benefit of the delivery optics is a smaller laser spot at the target and significantly enhanced throughput relative to systems which rely on the divergence of the excitation laser beam. The CRT itself is a 10-inch Cassegrain optimized for this short standoff range with motor-driven focus adjustment. We executed a Raman measurement of acetone at a standoff of 2 m using a Midwest Laser 325 nm helium cadmium laser, an Ocean Optics USB2000 grating spectrometer (with uncooled CCD), and an Omega edge filter. We present the results overlayed with published reference spectra. To the best of our knowledge, this is the first reported standoff Raman measurement performed with an uncooled CCD detector.
We present a new hyperspectral imaging system for the long wave infrared (LWIR) based on a tunable first-order Fabry-Perot Scanning Spectrometer (FPSS). The FPSS operates over 8 O 12 micrometers with a spectral resolution of 1% of the wavelength. The FPSS has a 22 degree field of view and a spatial resolution of 0.11 degrees. The key components of the FPSS system are the collection optics, a tunable Fabry-Perot etalon, optical position sensors, a closed-loop positioning system, an uncooled microbolometer focal plane array, a digital frame grabber card, and a user-friendly Graphical User Interface (GUI).
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