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  • 1
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    Sapphire fiber interferometer for microdisplacement measurements at high temperatures (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We report the use of a short-length, multimode sapphire rod as an extension to a Michelson configuration, but operated as a low-finesse Fabry-Perot cavity. We demonstrate the performance of such a device as an interferometric sensor, where the interference between the reflections from the sapphire-air interface and an air-metallic surface is observed for microdisplacement of the metallic surface which is placed close to the sapphire endface. We describe in detail the fabrication procedure and present results obtained from the detection of temperature changes, applied strain, and surface acoustic waves.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Fiber optic smart structures and skins IV; Proceedings of the Meeting, Boston, MA, Sept. 5, 6, 1991 (A93-21068 06-35); p. 117-124.
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  • 2
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    Multiresponse imaging system design for improved resolution (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Multiresponse imaging is a process that acquires A images, each with a different optical response, and reassembles them into a single image with an improved resolution that can approach 1/sq rt A times the photodetector-array sampling lattice. Our goals are to optimize the performance of this process in terms of the resolution and fidelity of the restored image and to assess the amount of information required to do so. The theoretical approach is based on the extension of both image restoration and rate-distortion theories from their traditional realm of signal processing to image processing which includes image gathering and display.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: ; : Problems in the ae
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  • 3
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    The Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: AVIRIS is a facility consisting of a flight system, a ground data system, a calibration facility, and a full-time operations team. The facility was developed by JPL under funding from NASA. NASA also provides funding for operations and maintenance. The flight system is a whisk-broom imager that acquires data in 224 narrow, contiguous spectral bands covering the solar reflected portion of the electromagnetic spectrum. It is flown aboard the NASA high altitude ER-2 research aircraft. The ground data system is a facility dedicated to the processing and distribution of data acquired by AVIRIS. It operates year round at JPL. The calibration facility consists of a calibration laboratory at JPL and a suite of field instruments and procedures for performing inflight calibration of AVIRIS. A small team of engineers, technicians, and scientists supports a yearly operations schedule that includes 6 months of flight operations, 6 months of routine ground maintenance of the flight system, and year-round data processing and distribution. Details of the AVIRIS system, its performance history, and future plans are described.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Remote Sensing of Environment (ISSN 0034-4257); 44; 2-3; p. 127-143.
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  • 4
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    Quantitative measurement of in-plane acoustic field components using surface-mounted fiber sensors (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Extrinsic Fabry-Perot interferometric sensors have been used to obtain calibrated, quantitative measurements of the in-plane displacement components associated with the propagation of ultrasonic elastic stress waves on the surfaces of solids. The frequency response of the sensor is determined by the internal spacing between the two reflecting fiber endface surfaces which form the Fabry-Perot cavity, a distance which is easily controlled during fabrication. With knowledge of the material properties of the solid, the out-of-plane displacement component of the wave may also be determined, giving full field data.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Fiber optic smart structures and skins V; Proceedings of the Meeting, Boston, MA, Sept. 8, 9, 1992 (A93-37326 14-35); p. 144-152.
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  • 5
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    Theory and operation of a three-gate time-of-flight velocity analyzer (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Theoretical considerations and test results are presented for a new-type velocity analyzer for incident fast neutral particles, positive ions, and negative ions. Velocity analysis is carried out by means of a pulsed, three-gate time-of-flight (TOF) technique capable of eliminating alias velocities (harmonics) to sixth order. In addition the design and operation are presented of a four-element ion lens system, with small spherical and chromatic aberrations, suitable for interfacing a large-diameter ion beam from the TOF section with a subsequent mass analyzer.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Review of Scientific Instruments (ISSN 0034-6748); 64; 2; p. 470-476.
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  • 6
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    Effect of trapped ions in a gated time-of-flight apparatus (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A three-mesh gate is used in a time-of-flight (TOF) apparatus to analyze the velocity of positive ions. Test results and a theoretical description are presented of an effect arising from trapping ions between meshes of a two-gate TOF velocity analyzer. The entrapped ions produce a side peak in the TOF spectra corresponding to faster ions. The onset and relative height of the side peak is dependent on the gating voltage and risetime of the pulsing electronics, while the relative intensity depends upon the velocity being sampled and the ratio of the gate width to duration.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Review of Scientific Instruments (ISSN 0034-6748); 64; 7; p. 1754-1757.
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  • 7
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    Two-mode elliptical-core weighted fiber sensors for vibration analysis (1992)
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    Publication Date: 2011-08-24
    Description: Two-mode, elliptical-core optical fibers are demonstrated in weighted, distributed and selective vibration-mode-filtering applications. We show how appropriate placement of optical fibers on a vibrating structure can lead to vibration mode filtering. Selective vibration-mode suppression on the order of 10 dB has been obtained using tapered two-mode, circular-core fibers with tapering functions that match the second derivatives of the modes of vibration to be enhanced. We also demonstrate the use of chirped, two-mode gratings in fibers as spatial modal sensors that are equivalents of shaped piezoelectric sensors.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Distributed and multiplexed fiber optic sensors; Proceedings of the Meeting, Boston, MA, Sept. 4, 5, 1991 (A93-49426 21-35); p. 53-66.
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  • 8
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    Current instrument status of the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: An upgraded version of AVIRIS, an airborne imaging spectrometer based on a whiskbroom-type scanner coupled via optical fibers to four dispersive spectrometers, that has been in operation since 1987 is described. Emphasis is placed on specific AVIRIS subsystems including foreoptics, fiber optics, and an in-flight reference source; spectrometers and detector dewars; a scan drive mechanism; a signal chain; digital electronics; a tape recorder; calibration systems; and ground support requirements.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Infrared technology XVII; Proceedings of the Meeting, San Diego, CA, July 22-26, 1991 (A93-38376 15-35); p. 164-175.
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  • 9
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    Theoretical model for a thin cylindrical film optical fiber fluorosensor (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The analytical treatment of power efficiency (P(eff) is undertaken for the case of a positively guiding optical fiber with a thin-film source distributed in the core-cladding interface. The approach adopts the exact solution of the cylindrical optical fiber with an infinite cladding to account for differences between the indices of refraction of the core and the cladding. The excitation of low-loss leaky modes by the cladding is ignored, and only the injection by the evanescent field is considered. The formulas permit the analysis of the power-injection efficiency of fibers with arbitrary differences in indices of refraction. P(eff) does not always increase with V number, but rather varies slightly with wavelength and fiber-core radius and varies significantly with the difference in the indices of refraction. The theoretical results of the work are of interest for designing an atomic-O chemical sensor based on evanescent-wave coupling.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Optical Engineering (ISSN 0091-3286); 31; 237-244
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  • 10
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    Laser velocimetry measurements in non-isothermal CVD systems (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Researchers at the NASA Langley Research Center are applying laser velocimetry (LV) techniques to characterize the fluid dynamics of non-isothermal flows inside fused silica chambers designed for chemical vapor deposition (CVD). Experimental issues involved in the application of LV techniques to this task include thermophoretic effects on the LV seed particles, seeding the hazardous gases, index of refraction gradients in the flow field and surrounding media, optical access, relatively low flow velocities, and analysis and presentation of sparse data. An overview of the practical difficulties these issues represent to the use of laser velocimetry instrumentation for CVD applications is given. A fundamental limitation on the application of LV techniques in non-isothermal systems is addressed which involves a measurement bias due to the presence of thermal gradients. This bias results from thermophoretic effects which cause seed particle trajectories to deviate from gas streamlines. Data from a research CVD reactor are presented which indicate that current models for the interaction of forces such as Stokes drag, inertia, gravity, and thermophoresis are not adequate to predict thermophoretic effects on particle-based velocimetry measurements in arbitrary flow configurations.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Laser anemometry - Advances and applications 1991; Proceedings of the 4th International Conference, Cleveland, OH, Aug. 5-9, 1991. Vol. 2 (A93-23776 08-35); p. 483-489.
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