Tech Briefs

Stochastic Representation of Chaos Using Terminal Attractors

Fictitious control forces stabilize what would otherwise be unstable computed trajectories. A nonlinear version of the Liouville equation based on terminal attractors is part of a mathematical formalism for describing postinstability motions of dynamical systems characterized by exponential divergences of trajectories leading to chaos (including turbulence as a form of chaos). The formalism can be applied to both conservative systems (e.g., multibody systems in celestial mechanics) and dissipative systems (e.g., viscous fluids).

Posted in: Briefs, TSP, Mechanical Components, Mechanics

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Lunar Constellation of Frozen Elliptical Inclined Orbits

A document discusses the design of orbits of spacecraft for relaying communications between Earth stations and robotic and human explorers in craters in one of the polar regions on the Moon. In simplest terms, the basic problem is to design a constellation of orbits to provide continuous and preferably redundant communication coverage of one of the poles with a minimal number of spacecraft and little or no controlled maneuvering of the spacecraft to maintain the orbits. The design method involves the use of analytical techniques for initial selection of orbits, followed by a numerical procedure for tuning the coverage of the constellation to obtain a design. In an example application, the method leads to a constellation of three spacecraft having elliptical, inclined orbits, the apoapsides of which would remain in the hemisphere (North or South) containing the pole of interest. The orbits would be stable and would maintain the required spacecraft formation for at least 10 years, without need for controlled maneuvering if gravitation is the only force considered to affect the orbits. A small amount of controlled maneuvering would be needed to counteract effects of solar-radiation pressure and other perturbations.

Posted in: Briefs, TSP, Mechanical Components, Mechanics

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Tunable, Highly Stable Lasers for Coherent Lidar

Designs have been refined to satisfy competing requirements for stability and tenability.Practical space-based coherent laser radar systems envisioned for global winds measurement must be very efficient and must contend with unique problems associated with the large platform velocities that the instruments experience in orbit. To compensate for these large platform-induced Doppler shifts in space-based applications, agilefrequency offset-locking of two singlefrequency Doppler reference lasers was thoroughly investigated. Such techniques involve actively locking a frequency- agile master oscillator (MO) source to a comparatively static local oscillator (LO) laser, and effectively producing an offset between MO (the lidar slave oscillator seed source, typically) and heterodyne signal receiver LO that lowers the bandwidth of the receiver data-collection system and permits use of very high-quantum-efficiency, reasonably- low-bandwidth heterodyne photoreceiver detectors and circuits. Similar techniques are being applied in atmospheric CO2 differential-absorption lidar work, where MO sources need to be actively offset-locked to CO2 reference cells for continuous absolute-calibration purposes. Active MO/LO offset- locking is also highly applicable to lidar problems involving very high target velocities with respect to a static or moving lidar platform.

Posted in: Briefs, Physical Sciences

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Optical Systems Improve Nerve Stimulation

An infrared laser-based nerve stimulation system eliminates electrical stimulation artifacts, and improves nerve target specificity.The stimulation of nerve tissue is a technique that is used in both research and clinical applications. Neuroscientists use nerve stimulation to study the fundamental principles of the nervous system and to research Parkinson’s disease, Alzheimer’s disease, and nerve regeneration, among others. Medical professionals use nerve stimulation for everything from pain and depression management to brain mapping. Today’s stimulators use electrical current to stimulate nerves, resulting in significant limitations. Thanks to a novel optical stimulation technique pioneered by Vanderbilt University, Aculight has developed a compact, laser-based neural stimulator that overcomes these obstacles.

Posted in: Briefs, Physical Sciences

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DPSS UV Source Targets Gas Lasers and Life Sciences

System is designed for applications that relied on pulsed nitrogen gas lasers Nitrogen lasers have been used for more than 15 years in life science and forensic applications and will continue to play a role in many scientific and industrial applications. But researchers, OEMs, and system integrators working on innovative, cutting-edge applications need higher-performance lasers. The Explorer, a diode-pumped solid-state OEM laser system with flexible power and control electronics, is a low-power, actively Qswitched, ultraviolet (UV) laser system that operates at 349 nm for bioinstrumentation applications that in the past have relied on pulsed nitrogen gas lasers.

Posted in: Briefs, Physical Sciences

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Optical Surface Analysis Advances Defect Inspection of Optoelectronics

Production defect data leads to better yield management practices. Faced with increasing demand, manufacturers of power devices, microdisplays, and high-brightness light-emitting diodes (HB-LEDs) are focusing on tightening manufacturing process windows to reduce defects. The transparent nature of the substrates used to make many optoelectronic devices such as glass, silicon carbide, and sapphire makes manual defect inspection using optical microscopes an ambiguous and timeconsuming process incapable of highvolume production. To meet the need for improved defect inspection, Optical Surface Analyzer (OSA) instruments provide automated defect inspection for optoelectronic device wafers from 2" to 300 mm in diameter.

Posted in: Briefs, Physical Sciences

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Tunable, Highly Stable Lasers for Coherent Lidar

Designs have been refined to satisfy competing requirements for stability and tenability. Marshall Space Flight Center, Alabama Practical space-based coherent laser radar systems envisioned for global winds measurement must be very efficient and must contend with unique problems associated with the large platform velocities that the instruments experience in orbit. To compensate for these large platform-induced Doppler shifts in space-based applications, agile-frequency offset-locking of two single-frequency Doppler reference lasers was thoroughly investigated. Such techniques involve actively locking a frequency-agile master oscillator (MO) source to a comparatively static local oscillator (LO) laser, and effectively producing an offset between MO (the lidar slave oscillator seed source, typically) and heterodyne signal receiver LO that lowers the bandwidth of the receiver data-collection system and permits use of very high-quantum-efficiency, reasonably-low-bandwidth heterodyne photoreceiver detectors and circuits. Similar techniques are being applied in atmospheric CO2 differential-absorption lidar work, where MO sources need to be actively offset-locked to CO2 reference cells for continuous absolute-calibration purposes. Active MO/LO offset-locking is also highly applicable to lidar problems involving very high target velocities with respect to a static or moving lidar platform.

Posted in: Briefs, ptb catchall, Tech Briefs, Photonics, Calibration, Lasers, Lidar

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