Based on the branch of physical science that studies the properties and phenomena of both visible and invisible light, the development, design and building of devices, processes or systems for the generation, propagation and implementation of the nature and behavior of electromagnetic light.
Multispectral Imaging, Detection, and Active Reflectance (MiDAR)
The MiDAR transmitter emits coded narrowband structured illumination to generate high-frame-rate multispectral video, perform real-time radiometric calibration, and provide a high-bandwidth simplex optical data-link under a range of ambient irradiance conditions, including darkness. A theoretical framework, based on unique color band signatures, is developed for multispectral video reconstruction and optical communications algorithms used on MiDAR transmitters and receivers. Experimental tests demonstrate a 7-channel MiDAR prototype consisting of an active array of multispectral high-intensity light-emitting diodes (MiDAR transmitter) coupled with a state-of-the-art, high-frame-rate NIR computational imager, the NASA FluidCam NIR, which functions as a MiDAR receiver. A 32-channel instrument is currently in development. Preliminary results confirm efficient, radiometrically-calibrated, high signal-to-noise ratio (SNR) active multispectral imaging in 7 channels from 405-940 nm at 2048x2048 pixels and 30 Hz. These results demonstrate a cost-effective and adaptive sensing modality, with the ability to change color bands and relative intensities in real-time, in response to changing science requirements or dynamic scenes. Potential applications of MiDAR include high-resolution nocturnal and diurnal multispectral imaging from air, space and underwater environments as well as long- distance optical communication, bidirectional reflectance distribution function characterization, mineral identification, atmospheric correction, UV/fluorescent imaging, 3D reconstruction using Structure from Motion (SfM), and underwater imaging using Fluid Lensing. Multipurpose sensors, such as MiDAR, which fuse active sensing and communications capabilities, may be particularly well-suited for mass-limited robotic exploration of Earth and the solar system and represent a possible new generation of instruments for active optical remote sensing.
High Output Maximum Efficiency Resonator (HOMER)
NASAs high performance laser has been extensively tested and analyzed to complete space-worthy Technology Readiness Level 6 (TRL-6). These tests include thermal vacuum test, vibration tests, and laser life testing. The HOMER enclosure is a pressurized vessel with sealed window and electrical feedthroughs for space. HOMERs design factors render the degradation rate to be remarkably low 100 uJ/B. These design factors being the heavy derating of the LDA drive parameters beginning of life (BOL) set point of 50 A, and 65 us in width. The other factor is the cavitys inherent large beam area, thus keeping longitudinal mode beating to a minimum, and thus peak temporal intensity spikes that can slowly pit coatings to an absolute minimum. HOMER is an oscillator only design that features an actively Q-switched cavity with an 808nm side pump Nd:YAG zig-ag slab, employing a positive branch unstable resonator and a Gaussian reflective output coupler for TEM00 far field beam quality. These cavities allow high pulse energies with beam quality and high efficiency without the need for intracavity aperture which can cause small scale self-focusing and degrading optical diffractive effects. Approximately 2-3 times the optics are typically required for an equivalent MOPA system. This important factor is critical in the instrument design phase of a flight project, when formulating the missions cost, mass, and overall hardware complexity.
Optimetric Measurements Over Coherent Free Space Optical Communication
NASA Goddard Space Flight Center has developed a directed modulated ranging technique to improve free space optical communications. Through utilizing coherent optical communication to combine optimetric measurements over an optical carrier, one can accurately measure Doppler and absolute ranging. This process works through a looping and synchronizing iteration, measuring frame, bit, and phase change values using a phase detector and clock data recovery apparatus. A dual mixer time difference (DMTD) approach is also employed, making the system more phase sensitive and easier to calibrate.
Coherent optical transistor
NASA Goddard Space Flight Center has developed a coherent optical transistor incorporating a coherent gain mechanism, resulting in larger and higher intensity signals present in optical logic systems. Moreover, the gain mechanism only adds a small amount of thermal energy, making the entire transistor easier to cool, reducing the overall size, weight, and power requirements.
Coating-Less Non-Planar Ring Oscillator Laser
The Coating-Less Non-Planar Ring Oscillator Laser utilizes a monolithic laser crystal, whose surfaces are precisely polished to form an optical cavity within the crystal, solely using total internal reflection (TIR). All surfaces of the laser use TIR, eliminating the need for any optical coatings. Frustrated TIR (FTIR) is used for the outer surface. The output coupler satisfies TIR, as does other reflection surfaces, which has a large enough angle of incidence for the internal ray. The ring resonator of the laser is also designed to be nonplanar, meaning the optical path is not on a flat plane. The Coating-Less Non-Planar Ring Oscillator Laser achieves high stability, high output power, and high reliability both in continuous wave mode and pulsed mode. It does not use any thin film optical coatings. Since there are no thin-film optical coatings in the laser cavity, one can expect more reliable laser operation and higher output power. Also, since it has a traveling wave cavity with internal polarization rotation mechanism (through the non-planar optical path), the output mode is ensured to be single longitudinal mode and stable. It also eliminates the possibility of damage due to the transition between the multi-mode and single-mode oscillation. A traditional NPRO crystal may be used as the laser crystal. Coupling of the FTIR can be adjusted to make an air-gap cube beam splitter, where the distance between the two surfaces determines the FTIR coupling strength. The laser crystal can be used both for Q-switching and continuous mode.
Video Acuity Measurement System
The Video Acuity metric is designed to provide a unique and meaningful measurement of the quality of a video system. The automated system for measuring video acuity is based on a model of human letter recognition. The Video Acuity measurement system is comprised of a camera and associated optics and sensor, processing elements including digital compression, transmission over an electronic network, and an electronic display for viewing of the display by a human viewer. The quality of a video system impacts the ability of the human viewer to perform public safety tasks, such as reading of automobile license plates, recognition of faces, and recognition of handheld weapons. The Video Acuity metric can accurately measure the effects of sampling, blur, noise, quantization, compression, geometric distortion, and other effects. This is because it does not rely on any particular theoretical model of imaging, but simply measures the performance in a task that incorporates essential aspects of human use of video, notably recognition of patterns and objects. Because the metric is structurally identical to human visual acuity, the numbers that it yields have immediate and concrete meaning. Furthermore, they can be related to the human visual acuity needed to do the task. The Video Acuity measurement system uses different sets of optotypes and uses automated letter recognition to simulate the human observer.
On-demand, Dynamic Reconfigurable Broadcast Technology for Space Laser Communication
NASA Goddard Space Flight Center has developed a configurable phase mirror system that can address likely obstacles in space optical communications. Through using miniature adjustable mirrors and programmed phase delays to diffract a single communication beam, numerous diffracted beams can be sent to other satellites in various directions for communication and tracking. The initial laser beams wave profile can be dynamically regulated through a fast Fourier transform (FFT) so that when it reaches its desired destination, it forms an intended illuminated spot at the target satellite. Since all the diffracted beams share the same phase mirror, the antenna gain needed to broadcast these beams does not require a multiplied aperture.
Digital Beamforming Interferometry
NASA Goddard Space Flight Center (GSFC) has developed a new approach that uses a single phased array antenna and a single pass configuration to generate interferograms, known as Digital Beamforming Interferometry. A digital beamforming radar system allows the implementation of non-conventional radar techniques, known as Digital Beamforming Synthetic Aperture Radar Multi-mode Operation (DBSAR). DBSAR is an L-Band airborne radar that combines advanced radar technology with the ability to implement multimode remote sensing techniques, including several variations of SAR, scatterometry over multiple beams, and an altimeter mode. The Multiple channel data acquired with a digital beamformer systems allows the synthesis of beams over separate areas of the antenna, effectively dividing the single antenna into two antennas. The InSAR technique is then achieved by generating interferograms from images collected with each of the antennas. Since the technique is performed on the data, it allows for synthesizing beams in different directions (or look angles) and performs interferometry over large areas. Digital Beamforming Interferometry has potential in many areas of radar applications. For example, NASA GSFC innovators developed the first P-Band Digital Beamforming Polarimetric Interferometric SAR Instrument to measure ecosystem structure, biomass, and surface water.
High-Resolution, Continuous Field-of-View, Nonrotating Imaging System
JPL's high-resolution complementary metal-oxide semiconductor (CMOS) imaging system comprises two major elements: a sensor head for scene acquisition and a control apparatus with distributed processors and software for device control, data handling, and display. The sensor head is configured as a cylinder suitable for use on the existing mast of conventional periscopes and has seven decks. Each deck encloses a combination of wide-FOV CMOS imagers (i.e., full-field imagers [FFIs]) and narrow-FOV CMOS imagers (i.e., tracking zoom imagers [TZIs]). The control apparatus includes four TZI processors, one FFI processor, one host processor, and an optional automatic target recognition (ATR) processor for high-speed, high-precision target detection, identification, and tracking. A high-resolution, continuous FOV, nonrotating imaging system has been demonstrated using readily available CMOS imagers. The image processing and system-level control electronics are instantiated in six conventional PC104 stacks (one for each processor) and contained in a 10x50x20-cm housing, which has a footprint approximately the size of a standard laptop computer. The display system is computer workstation hosting an interactive graphical user interface that allows the user to exercise all of the operational states of the system (e.g., search, tracking, display, high-resolution windowing, etc.).
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