Photonics/Optics

Electrically Tunable Terahertz Quantum-Cascade Lasers

These devices would supplant gas lasers as far-infrared sources. NASA’s Jet Propulsion Laboratory, Pasadena, California Improved quantum-cascade lasers (QCLs) are being developed as electrically tunable sources of radiation in the far infrared spectral region, especially in the frequency range of 2 to 5 THz. (Heretofore, the wavelengths of QCLs have been adjusted by changing temperatures, but not by changing applied voltages or currents.) In comparison with gas lasers now used as far-infrared sources, these QCLs would have larger wavelength tuning ranges, would be less expensive, and would be an order of magnitude less massive and power-hungry. It is planned to use the improved QCLs initially as the active components of local oscillators in spaceborne heterodyne instruments for studying infrared spectral lines of molecules of scientific interest. On Earth, the QCLs could be used as far-infrared sources for medical glucose-monitoring and heart-monitoring instruments, chemical-analysis and spectral-imaging systems, and imaging instruments that exploit the ability of terahertz radiation to penetrate cloth and walls for detection of contra-band weapons.

Posted in: Briefs, ptb catchall, Tech Briefs, Photonics, Lasers, Medical equipment and supplies, Radiation, Test equipment and instrumentation

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Fiber-Optic Liquid-Level Sensors

Liquid-level-measuring systems based on fiber-optics are under development as compact, lightweight alternatives to systems based on float gauges and other conventional sensors. For liquids that pose explosion hazards, fiber-optic sensors are inherently safer because they do not include electrical connections inside tanks. Fiber-optic sensors can be designed in many different forms to exploit reflection and transmission of light to measure liquid levels. Most of them are based on the effects of the indices of refraction of liquids on the waveguide properties of optical fibers: In a typical case, there is a loss of internal reflection of guided electromagnetic modes as a result of contact between the outer surface of optical fiber and a liquid. Hence, a substantial decrease in the light transmitted from one end of the fiber to the other is taken to indicate that liquid has come into contact with a suitably designed probe at the end of the fiber. A system capable of determining the level of liquid to within a known increment of depth could be constructed by placing the probes of a number of such sensors at known increments of depth in a tank.

Posted in: Briefs, Tech Briefs, Photonics, Fiber optics, Waveguides, Fuel sensors

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Generalized-Time-Line Program for Planning and Scheduling

Generalized Timelines API is a computer program that provides (1) a means of representing arbitrary realworld state and resource information for use in planning, scheduling, and plan- and schedule-executing software and (2) an application-programming interface (API) that accelerates the development and validation of the software. In prior time-line programs, constraints had not been regarded as parts of time lines, and it was difficult to represent constraints. For the present program, a time line is defined as a representation of the actual and/or predicted value(s) of a variable and a set of constraints on the variable, both at successive intervals of time. The program (1) enables assignment of values to variables and modeling of the constraints on the variables, all as functions of time; (2) makes it possible to determine whether the values are consistent with the constraints; and (3) provides “hooks” to the search space represented by the variables for the purpose of optimizing plans. This program enables computer-programming specialists to engage in research on, and development of, scheduling application programs separately from the efforts of other specialists to implement time lines specific to their domains of expertise. In comparison with prior software of the same type, this program is representationally sufficient for more domains.

Posted in: Briefs, TSP, ptb catchall, Tech Briefs, Photonics, Computer software and hardware, Systems management

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Compact, Stiff, Lightweight, Quick-Release Clamp

This clamp offers several advantages over a prior toggle-action clamp. The term "COSMOWRAP" denotes a compact, stiff, remotely actuatable, lightweight, quick-release clamp that could be substituted for the larger, heavier, and more-difficult-to-use toggle-action clamp now used in the space shuttle orbiter docking system (ODS) to perform contingency separations. In comparison with prior hand-operated devices designed for the same purpose, the COSMOWRAP is smaller and lighter in weight, yet offers greater capabilities. The COSMOWRAP (see figure) contains no spring and requires no pre-flight calibration or maintenance. The COSMOWRAP is expected to perform well, not only in the space-shuttle application for which it was originally designed, but also in terrestrial applications. Because the design of the COSMOWRAP reduces the force needed for installation or removal and provides for release by the action of one hand, the replacement of the ODS toggle-action clamp by the COSMOWRAP can be expected to contribute to crew safety in the United States space program and on the International Space Station.

Posted in: Briefs, ptb catchall, Tech Briefs, Photonics, Tools and equipment, Product development, Fasteners, Reusable launch vehicles and shuttles

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Hand-Held Optoelectronic Particulate Monitors

Data on concentrations and sizes are obtained from diffraction of light. Optoelectronic instruments are being developed for use in measuring the concentrations and sizes of microscopic particles suspended in air. The instruments could be used, for example, to detect smoke, explosive dust in grain elevators, or toxic dusts in industrial buildings. Like some older, laboratory-bench-style particulate monitors, these instruments are based on diffraction of light by particles. However, these instruments are much smaller; exploiting recent advances in optics, electronics, and packaging, they are miniaturized into compact, hand-held units.

Posted in: Briefs, TSP, ptb catchall, Tech Briefs, Photonics, Physical Sciences, Downsizing, Measurements, Microscopy, Optics, Particulate matter (PM)

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High-Performance Processor of Hyperspectral Images

Efficient algorithms analyze pixel spectra to estimate abundances of materials. The Remote Sensing Hyperspectral Engine (RSHE) is a special-purpose, portable computer that performs high-performance processing of hyperspectral image data collected by a remote-sensing optoelectronic apparatus. Typically, the remote-sensing apparatus is airborne or spaceborne, the images are of terrain, and the purpose of collecting and analyzing the image data is to estimate the spatially varying abundances of materials of interest. Remote-sensing applications in which the RSHE could prove beneficial include assessment of crops, exploration for minerals, identification of military targets, urban-planning studies, environmental assessment, and large-area search-and- rescue operations.

Posted in: Briefs, Tech Briefs, Photonics, Computer software and hardware, Imaging and visualization, Remote sensing, Data management

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Lateral-Current-Collection HgCdTe Infrared Detectors

Improvements in yield and electrical performance are obtained. Arrays of HgCdTe infrared photodetectors have been developed to satisfy stringent performance requirements for use in NASA’s Tropospheric Emission Spectrometer. The design of these detectors improves (relative to prior such arrays) manufacturing yield, current-versus-voltage characteristics, and low-temperature performance. The design is of the doublelayer planar heterostructure (DLPH) type but differs from conventional DLPH designs in that it features a distinctive lateral current-collection configuration.

Posted in: Briefs, TSP, ptb catchall, Tech Briefs, Electronics & Computers, Photonics, Sensors and actuators, Spectroscopy, Product development, Performance tests

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