There is a worldwide interest in developing a sensing system for the online detection and chemical
identification of hazardous substances, especially in water and in air. Towards this goal we have
developed an evanescent wave spectroscopy system based on a tunable CO2 on an IR detector and
on thin AgBr flat waveguides, which were transparent in the mid-IR and served as sensing elements.
Aqueous solutions of common pesticides (e.g. DDVP, Parathion, Diazinon) were placed on the
waveguide and spectral absorption measurements were performed in the mid-IR. Using the results,
we were able to detect these pesticides at concentrations as low as few ppm and distinguish between
them. Such a system would be invaluable for homeland security applications.
During the last decade, there has been rapid progress in the development of integrated optical circuits, incorporating thin optical waveguides, for the Visible and Near IR (NIR) spectral ranges. In this work we extended the same concept to the Mid-IR (MIR) spectral range 3-30 microns. Towards this goal we developed diffused and strip buried planar waveguides based on silver halide crystals.
Diffused planar waveguides were created by diffusion of Br- ions into crystalline substrates, forming silver chloro-bromide (AgClBr) layers of higher refractive indices and different thickness of 65μm to 600μm. Strip buried planar waveguides were constructed from press-flattened silver chloro-bromide (AgClBr) fibers with different thickness, which were buried into an almost pure substrate. All the waveguides were in a thickness range of 60μm to 170μm. Using CO2 laser we found that the transmission losses at 10.6mm were about 4 to 12dB/cm for the buried waveguides and about 4 to 16dB/cm for the diffused waveguides. We also formed and characterized curved waveguides on AgCl substrate.
By using the planar waveguides as sensing elements for infrared evanescent wave spectroscopy, we were able to detect 1% of glucose or 1% of alcohol in water. In conclusion, we demonstrate the feasibility of using AgClBr waveguides as integrated optical elements in the MIR.
A simple thermal imaging system based on silver halide fibers or glass hollow waveguides was constructed. The proximal end of each type of waveguide was fixed and attached to an infrared detector. The distal end of each waveguide was scanning in two directions. Such a device was used to construct a simple imaging system. The thermal image of a warm object may be formed at the focal plane of an infrared lens. The distal end of each waveguide scanned the image. The infrared radiation was transmitted through the waveguide to the detector. The signals from the detector were coupled into a suitable monitor that produced a representation of the thermal image. In preliminary experiments we used an unclad silver halide fiber of diameter 0.7 mm, and a hollow glass waveguide of diameter of 0.5 mm. A permanent magnet was attached to the end tip of each waveguide, and it was displaced by a varying electro magnetic field. The detector used was a room temperature pyroelectric detector. A MTF of about 0.2 at a spatial frequency of 1.25 cycles/mm, and a MRTD of 0.50 Celsius deg at 0.1 cycles/mm were obtained with this simple imaging system.
A CO2 laser device based on a scanner Silver halide infrared (IR) optical fiber was designed and constructed. Power delivery was performed by scanning the output end of the optical fiber in two dimensions. A permanent magnet was attached to this end of the fiber, and it was displaced by a varying electromagnetic field. The device is computerized, which enables control of the scanning speed, laser output and magnetic field strength. Powered by a CO2 laser, the equipment is capable of cutting, heating or marking various surfaces. This paper describes applications in which CO2 laser energy is guided to remote locations via IR optical fiber. The output profile distribution, spot size and resolution were investigated and the results are compared to a simple theoretical model.
KEYWORDS: Stars, Signal to noise ratio, Charge-coupled devices, Image processing, Digital signal processing, Electronics, Satellites, Electrons, Detection and tracking algorithms, Sensors
This paper describes a star tracker (ST) as a major sub-system of an autonomous satellite navigation system. The navigation system is comprised of a star tracker which determines the satellite attitude and a Global Positioning System (GPS) receiver which determines the satellite's position. The ST is based on a thermoelectrically cooled CCD camera, wide field of view optics with an optical baffle, and an electronic processing unit. The (ST) is a smart sensor that performs acquisition and recognition processes by comparing the CCD captured sky image with a stored star catalog map. The wide field of view optics makes possible the computation of the three-axis attitude from a single exposure. It also decreases the required computation time due to a need of a smaller star catalog and a more effective star identification procedure. The design consideration, star recognition algorithms, and electronic hardware are described. An accuracy of about 100 (mu) rad is expected by the use of a centroid algorithm and a special image processing technique.
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