Photonics/Optics

Development of Sodium Lidar for Spaceborne Missions

The metal layers at mesospheric altitudes are excellent tracers of neutral atmosphere dynamics, and have been used since the 1960s to study the chemistry and dynamics of the mesosphere. Ablation from meteors is believed to be the chief source of metals such as Na, Mg, K, Fe, and Ca in the middle atmosphere. Due to its relative abundance, large backscatter cross-section, and visible atomic transition, sodium (Na) has been used extensively for lidar studies of the mesosphere.

Posted in: Briefs, Photonics
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Additive-Manufactured, Very Lightweight, Diamond Turned Aspheric Mirror

Industrial-grade, lightweight mirrors used in military and aeronautics have tight specifications brought on by demanding performance parameters. For example, a mirror that is used in an orbiting telescope would have to be extremely lightweight, stiff, and be configured to operate in extreme temperatures. These parameters traditionally work against each other. A material that is stiff is typically heavy, and a mirror that is lightweight and machinable may greatly distort when exposed to extreme heat or cold. Furthermore, materials that fit some of these parameters may not be easily machined to create a mirror, an art that requires high-precision tooling.

Posted in: Briefs, Photonics
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Partially Transparent Circular Mask to Suppress Narrowband Laser Light

The evolved Laser Interferometry Space Antenna (eLISA) is the implementation of the original Laser Interferometry Space Antenna (LISA) concept that will be proposed for the European Space Agency's (ESA) L.3 Cosmic Visions opportunity. The eLISA observatory uses lasers to range between pairs of freely falling test masses in adjacent, widely separated spacecraft. The measurement is made continuously, requiring simultaneous transmission and reception of a 1064-nm laser beam through an optical telescope.

Posted in: Briefs, Photonics
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Characterizing Richness of Previously Unmapped Terrain and Estimating Its Impact on Navigation Performance Using 3D Range Sensors in Flight

Landers to large planetary bodies such as Mars typically use a secondary reconnaissance spacecraft to generate high-fidelity 3D terrain maps that are subsequently used for landing site selection and creating onboard maps for terrain-relative navigation systems. This luxury does not exist with small primitive bodies such as comets and asteroids. For these bodies, the landing spacecraft has to perform the 3D mapping and, with possible help from ground control, choose a feasible landing site. To enable this operation, the spacecraft would need to carry a 3D ranging sensor system such as a LIDAR. With the spacecraft placed in extended mapping orbits, 3D range measurement data is then used to create a shape model of the object. Terrain-based navigation schemes that employ cameras could then be used to image, detect, match, and track features against the map database to provide a 6-degrees-of-freedom (DOF) navigation solution during descent. Camera-based systems, however, are not robust to lighting variations, and do not provide a direct 3D position/range feedback.

Posted in: Briefs, Photonics
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Micro-Fresnel Zone Plate Optical Devices Using Densely Accumulated Ray Points

NASA Langley Research Center has developed a novel approach for a high-density optical data storage system to advance the typical capabilities of an optical data storage system. Operating at any laser wavelength from infrared (IR), visible, ultraviolet (UV), and X-ray regimes, the NASA technology utilizes special beam focusing techniques to achieve extremely short focal lengths and ultra-small spot sizes. The technology could be used with any laser wavelength and soft X-ray regime, and can be adapted to take advantage of any optical media. The high-density data storage capability is solely a function of the reduced laser/X-ray spot size.

Posted in: Briefs, Photonics, Lasers, Optics, Waveguides, Data management
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CUDA Framework for Linear Time-Invariant Control of Adaptive Optics Systems

The predictor used here is computed directly from a measured open-loop disturbance sequence using an efficient subspace identification algorithm.

Current science objectives, such as high-contrast imaging of exoplanets, have led to the development of highorder adaptive optics (AO) systems possessing several thousand deformable mirror (DM) actuators. These systems typically rely on integrator-based control architectures, where the temporal error rejection bandwidth is limited by the computational latency between wavefront measurement and application of the DM commands. In many systems, this latency is the driving factor behind residual wavefront error.

Posted in: Briefs, Photonics, Mirrors, Adaptive control, Architecture, Computer software and hardware, Optics, Sensors and actuators
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Arrayed Micro-Ring Spectrometer System and Method of Use

This miniaturized system performs rapid multi-spectral analysis and imaging.

NASA Langley Research Center has developed a novel spectral analysis system that provides rapid multispectral analysis and imaging in a miniaturized system design. Typical spectrometers make use of linear gratings with linear slits or charge-coupled device (CCD) arrays to separate and detect light in its component wavelengths to build a spectrum across a range of wavelengths. Such conventional spectrometers are difficult to miniaturize below a few centimeters. Creating an image with these systems also requires physical rastering of the light beam and detection system across an area to build up the individual data points of an image. The NASA Micro-Ring Thin-Film Spectrometer technology makes use of a microring grating to separate the component wavelengths of the light signal for detection and spectral analysis. Due to the miniaturized design obtained by Fresnel diffraction, an array of these micro-ring grating-based spectrometers can be constructed to enable extremely small-size, multi-spectral imaging of an analysis area.

Posted in: Briefs, Photonics, Downsizing, Spectroscopy, Product development, Refractory materials
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Resonance-Actuation of Microshutter Arrays

This innovation uses MEMS technology to selectively capture spectra of distant objects.

The field of view required for future missions is much larger than for the James Webb Space Telescope (JWST). Researchers at NASA’s Goddard Space Flight Center have created a new actuation scheme to reduce mass and complexity of the microshutters used on the NIRSpec instrument. This new development implements pulsed electrostatic actuation in place of magnetic actuation.

Posted in: Briefs, Photonics, Optics, Sensors and actuators, Product development, Refractory materials
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A Novel Orbiting Cloud Imager System for IR/UV/ X-Ray Bands

Applications include telecommunications involving satellite links, agile military communication, reconnaissance, and surveillance of ground assets from orbit.

Typically, the cost of a spaceborne imaging system is driven by the size and mass of the primary aperture. Innovative solutions for imagers that are less complex and are lightweight are very desirable. Currently, telescopes such as JWST and ATLAST are very expensive and very complex.

Posted in: Briefs, Photonics, Downsizing, Optics, Lightweighting, Satellites
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2.2-Micron, Uncooled, InGaAs Photodiodes and Balanced Photoreceivers up to 25-GHz Bandwidth

These photodiodes have applications in LiDAR sensors, telecommunications links, and pulsed laser systems.

Traditional applications for 2-micron photodetectors have been largely dominated by passive remote sensing where detectors having bandwidth of even one megahertz are deemed sufficient. The onus in such applications is to achieve low dark current through active cooling. The advent of high-power, 2-micron-wave-length lasers have made coherent LiDARs viable for active sensing applications. Such a system needs photodetectors that can handle high local oscillator optical power and have large bandwidth. Through a combination of high coherent gain and small integration time, a large signal-to-noise ratio can be achieved. Operation at high optical power levels reduces the significance of photodiodes’ dark current. As a result, uncooled operation at room temperature is feasible, simplifying the overall instrument design.

Posted in: Briefs, Photonics, Optics, Remote sensing, Cooling
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