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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
NASA NTRS2006

Long-Wavelength Infrared (LWIR) Quantum Dot Infrared Photodetector (QDIP) Focal Plane Array

We have exploited the artificial atomlike properties of epitaxially self-assembled quantum dots for the development of high operating temperature long wavelength infrared (LWIR) focal plane arrays. Quantum dots are nanometer-scale islands that form spontaneously on a semiconductor substrate due to lattice mismatch. QDIPs are expected to outperform quantum well infrared detectors (QWIPs) and are expected to offer significant advantages over II-VI material based focal plane arrays. QDIPs are fabricated using robust wide bandgap III-V materials which are well suited to the production of highly uniform LWIR arrays. We have used molecular beam epitaxy (MBE) technology to grow multi-layer LWIR quantum dot structures based on the InAs/InGaAs/GaAs material system. JPL is building on its significant QWIP experience and is basically building a Dot-in-the-Well (DWELL) device design by embedding InAs quantum dots in a QWIP structure. This hybrid quantum dot/quantum well device offers additional control in wavelength tuning via control of dot-size and/or quantum well sizes. In addition the quantum wells can trap electrons and aide in ground state refilling. Recent measurements have shown a 10 times higher photoconductive gain than the typical QWIP device, which indirectly confirms the lower relaxation rate of excited electrons (photon bottleneck) in QDPs. Subsequent material and device improvements have demonstrated an absorption quantum efficiency (QE) of approx. 3%. Dot-in-the-well (DWELL) QDIPs were also experimentally shown to absorb both 45 deg. and normally incident light. Thus we have employed a reflection grating structure to further enhance the quantum efficiency. JPL has demonstrated wavelength control by progressively growing material and fabricating devices structures that have continuously increased in LWIR response. The most recent devices exhibit peak responsivity out to 8.1 microns. Peak detectivity of the 8.1 micrometer devices has reached approx. 1 x 10(exp 10) Jones at 77 K. Furthermore, we have fabricated the first long-wavelength 640x512 pixels QDP focal plane array. This QDIP focal plane may has produced excellent infrared imagery with noise equivalent temperature difference of 40 mK at 60K operating temperature. In addition, we have managed to increase the quantum efficiency of these devices from 0.1% (according to the data published in literature) to 20% in discrete devices. This is a factor of 200 increase in quantum efficiency. With these excellent results, for the first time QDIP performance has surpassed the QWIP performance. Our goal is to operate these long-wavelength detectors at much higher operating temperature than 77K which can be passively achieved in space. This will be a huge leap in high performance infrared detectors specifically applicable to space science instruments.

infrared imaging↗
DOE OSTI2024

Resolving the Electron Plume within a Scanning Electron Microscope

Scanning electron microscopy (SEM), a century-old technique, is today a ubiquitous method of imaging the surface of nanostructures. However, most SEM detectors simply count the number of secondary electrons from a material of interest, and thereby overlook the rich material information contained within them. Here, by simple modifications to a standard SEM tool, we resolve the momentum and energy information on secondary electrons by directly imaging the electron plume generated by the electron beam of the SEM. Leveraging these spectroscopic imaging capabilities, our technique is able to image lateral electric fields across a prototypical silicon p–n junctions and to distinguish differently doped regions, even when buried beyond depths typically accessible by SEM. Intriguingly, the subsurface sensitivity of this technique reveals unexpectedly strong surface band bending within nominally passivated semiconductor structures, providing useful insights for complex layered component designs, in which interfacial dynamics dictate device operation. Further, these capabilities for noninvasive, multimodal probing of complicated electronic components are crucial in today’s electronic manufacturing but is largely inaccessible even with sophisticated techniques. These results show that seemingly simple SEM can be extended to probe complex and useful material properties.

36 MATERIALS SCIENCE↗
NASA NTRS1978

Contour Detector and Data Acquisition System for the Left Ventricular Outline

A real-time contour detector and data acquisition system is described for an angiographic apparatus having a video scanner for converting an X-ray image of a structure characterized by a change in brightness level compared with its surrounding into video format and displaying the X-ray image in recurring video fields. The real-time contour detector and data acqusition system includes track and hold circuits; a reference level analog computer circuit; an analog compartor; a digital processor; a field memory; and a computer interface.

Reiber, J. H. C.↗
NASA NTRS1983

Thematic mapper intraband radiometric performance

There are small differences between the average DN for the 16 detectors in each band, typically 0.8 DN; the standard deviations also differ typically by 0.4 DN. Differences of mode in a band are as large as 6 DN. Some DN levels appear to be strongly favored over adjacent levels. Differences between forward and reverse scans are approximately 0.1 DN in the mean, and 0 to 0.6 DN in the standard deviation. Geometrically resampled images (P data), in which the fixed correspondence between lines and single detectors is lost, are statistically similiar to the ensemble of detectors in each band in A data. The magnitude of inter-detector variation is readily seen by making an image of the first derivative in the vertical (line) direction of a flat field and stretching progressively wider ranges to gray; most detectors differ from their neighbors by 1 to 2 DN. The film output from the GSFC filmwriter used for TM images was found to have scale errors in both sample and line directions corresponding to four pixels in a TM image, and skew corresponding to three pixels.

Kieffer, H. H.↗
NASA NTRS2008

Performance of the JWST/MIRI Si:As Detectors

The Mid-Infrared Instrument (MIRI) is a 5 to 28 micron imager and spectrometer that is slated to fly aboard the JWST in 2013. Each of the flight arrays is a 1024x1024 pixel Si:As impurity band conductor detector array, developed by Raytheon Vision Systems. JPL, in conjunction with the MIRI science team, has selected the three flight arrays along with their spares. We briefly summarize the development of these devices, then describe the measured performance of the flight arrays along with supplemental data from sister flight-like parts.

arsenic-doped silicon↗
NASA NTRS1987

Combined optimization of image-gathering and image-processing systems for scene feature detection

The relationship between the image gathering and image processing systems for minimum mean squared error estimation of scene characteristics is investigated. A stochastic optimization problem is formulated where the objective is to determine a spatial characteristic of the scene rather than a feature of the already blurred, sampled and noisy image data. An analytical solution for the optimal characteristic image processor is developed. The Wiener filter for the sampled image case is obtained as a special case, where the desired characteristic is scene restoration. Optimal edge detection is investigated using the Laplacian operator x G as the desired characteristic, where G is a two dimensional Gaussian distribution function. It is shown that the optimal edge detector compensates for the blurring introduced by the image gathering optics, and notably, that it is not circularly symmetric. The lack of circular symmetry is largely due to the geometric effects of the sampling lattice used in image acquisition. The optimal image gathering optical transfer function is also investigated and the results of a sensitivity analysis are shown.

Halyo, Nesim↗
NASA NTRS1986

Wide-angle flat field telescope

Described is an unobscured three mirror wide angle telescopic imaging system comprised of an input baffle which provides a 20 deg (Y axis) x 30 deg (X axis) field of view, a primary mirror having a convex spherical surface, a secondary mirror having a concave ellipsoidal reflecting surface, a tertiary mirror having a concave spherical reflecting surface. The mirrors comprise mirror elements which are offset segments of parent mirrors whose axes and vertices commonly lie on the system's optical axis. An iris diaphragm forming an aperture stop is located between the secondary and tertiary mirror with its center also being coincident with the optical axis and being further located at the beam waist of input light beams reflected from the primary and secondary mirror surfaces. At the system focus following the tertiary mirror is located a flat detector which may be, for example, a TV imaging tube or a photographic film. When desirable, a spectral transmission filter is placed in front of the detector in close proximity thereto.

Hallam, K. L.↗
NASA NTRS1969

Selective vignetting of Type 1 X-ray telescopes

Selective vignetting technique optimizes the performance of a Type 1 X-ray telescope. The image quality of the telescope system is improved by matching the detector to the optimum focal surface and by vignetting rays which formerly contributed to the flare in comatic images.

Mangus, J.↗
NASA NTRS1981

Image motion compensation on the Spacelab 2 Solar Optical Universal Polarimeter /SL2 SOUP/

The SOUP experiment on Spacelab 2 includes a 30 cm visible light telescope and focal plane package mounted on the Instrument Pointing System (IPS). Scientific goals of the experiment dictate pointing stability requirements of less than 0.05 arcsecond jitter over periods of 5-20 seconds. Quantitative derivations of these requirements from two different aspects are presented: (1) avoidance of motion blurring of diffraction-limited images; (2) precise coalignment of consecutive frames to allow measurement of small image differences. To achieve this stability, a fine guider system capable of removing residual jitter of the IPS and image motions generated on the IPS cruciform instrument support structure has been constructed. This system uses solar limb detectors in the prime focal plane to derive an error signal. Image motion due to pointing errors is compensated by the agile secondary mirror mounted on piezoelectric transducers, controlled by a closed-loop servo system.

Tarbell, T. D.↗
NASA NTRS1993

Nature's crucible: Manufacturing optical nonlinearities for high resolution, high sensitivity encoding in the compound eye of the fly, Musca domestica

The number of pixels per unit area sampling an image determines Nyquist resolution. Therefore, the highest pixel density is the goal. Unfortunately, as reduction in pixel size approaches the wavelength of light, sensitivity is lost and noise increases. Animals face the same problems and have achieved novel solutions. Emulating these solutions offers potentially unlimited sensitivity with detector size approaching the diffraction limit. Once an image is 'captured', cellular preprocessing of information allows extraction of high resolution information from the scene. Computer simulation of this system promises hyperacuity for machine vision.

Wilcox, Mike↗
NASA NTRS1993

Imaging Spectrometers Using Concave Holographic Gratings

Imaging spectroscopy combines the spatial attributes of imaging with the compositionally diagnostic attributes of spectroscopy. For spacebased remote sensing applications, mass, size, power, data rate, and application constrain the scanning approach. For the first three approaches, substantial savings in mass and size of the spectrometer can be achieved in some cases with a concave holographic grating and careful placement of an order-sorting filter. A hologram etched on the single concave surface contains the equivalent of the collimating, dispersing, and camera optics of a conventional grating spectrometer and provides substantial wavelength dependent corrections for spherical aberrations and a flat focal field. These gratings can be blazed to improve efficiency when used over a small wavelength range or left unblazed for broadband uniform efficiency when used over a wavelength range of up to 2 orders. More than 1 order can be imaged along the dispersion axis by placing an appropriately designed step order-sorting filter in front of the one- or two-dimensional detector. This filter can be shaped for additional aberration corrections. The VIRIS imaging spectrometer based on the broadband design provides simultaneous imaging of the entrance slit from lambda = 0.9 to 2.6 microns (1.5 orders) onto a 128 x 128 HgCdTe detector (at 77 K). The VIRIS spectrometer was used for lunar mapping with the UH 24.in telescope at Mauna Kea Observatory. The design is adaptable for small, low mass, space based imaging spectrometers.

Gradie, J.↗
DOE OSTI2020

Performance of 8 × 8 × 32 and 10 × 10 × 32 mm 3 CdZnTe position-sensitive virtual Frisch-grid detectors for high-energy gamma ray cameras

CdZnTe (CZT) crystals with thicknesses up to 20 mm and diameters up to 75 mm have become available from Redlen Technologies, Inc. for making large-volume gamma-ray detectors. The modified growth and optimized annealing conditions allowed Redlen to minimize the dark current and improve the uniformity of CZT crystals. Two detector designs, pixelated (H3D) and position-sensitive virtual Frisch-grid (VFG), have greatly benefitted from the availability of such big crystals. Encouraging results from testing of 40×40×15 mm 3 pixelated detectors were recently reported by the University of Michigan. In this work, we evaluated the spectroscopic properties of 8×8×32 and 10×10×32 mm 3 crystals configured as position-sensitive VFG detectors. Both digitized waveforms and an analog ASIC were used to read and process the signals from the detectors and test their spectral- and spatial-resolution. The VFG design provides the flexibility to scale-up the dimensions of the detectors for the desired efficiency, while the position information allows for correcting the detectors' response non-uniformity caused by crystal defects and devices geometry, thereby reducing the instrument cost and making them more feasible for emerging applications in gamma-ray astronomy, nonproliferation, portal screening and nuclear safeguards, where large detector arrays are often required.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1992

Application of the intensified CCD to airglow and auroral measurements

New detector technology exemplified by advanced CCD and intensified CCD (ICCD) systems have important advantages for both spectrographic and imaging research. However, to realize the full potential of this new technology, the detector and the optical system as a whole must be considered. It is frequently not enough to simply substitute an ICCD for an earlier detector; rather, to achieve optimum results, the optics must be adapted to the specific detector. Properly designed airglow spectrographs based on the ICCD detector offer the advantages of high throughput over a broad spectral range, precise wavelength stability, low noise, and compactness. Imagers having the wide field and the high sensitivity needed for airglow research are practical as well.

Broadfoot, A. L.↗
DOE OSTI2023

Understanding hadronic interactions using advanced reconstruction techniques

ProtoDUNE-SP served as the prototype of the future Deep Underground Neutrino Experiment (DUNE). With a total liquid argon mass of 0.77 kt, it stood as the most extensive monolithic single-phase Liquid Argon Time Projection Chamber (LArTPC) ever constructed. Strategically located and operated at CERN, ProtoDUNE-SP benefited from a specialized charged-particle test beam, offering a momentum range of 0.3 - 7 GeV/c. This setup provided a unique opportunity to conduct in-depth studies on hadronic interactions within argon. Hadronic interactions play a fundamental role in neutrino physics, particularly in the intricacies of neutrino detection. We depend on analyzing the outcomes of these interactions to accurately determine both the flavor and energy of the interacting neutrinos. Pions, as one of the primary byproducts of neutrino interactions, are crucial for understanding the overall dynamics and kinematics of these processes. Accurately characterizing and understanding the interaction of pions with argon can significantly enhance the precision of neutrino simulations and measurements.Being a Liquid Argon Time Projection Chamber (LArTPC), ProtoDUNE-SP is distinguished by its ability to produce high-definition images of charged particles as they traverse through the detector's active volume. Yet, accurately reconstructing these particle interactions and determining their kinematic attributes remains a challenging task. The successes of deep learning in diverse domains, especially in image recognition, provide a promising approach for addressing this challenge in ProtoDUNE. This thesis discusses a measurement of the Piplus - argon inelastic cross section in the energy range of 2400 to 3000 MeV, using data taken by protoDUNE during the fall of 2018. Additionally, panoptic segmentation, a machine learning technique, is introduced and validated through its application in the reconstruction of the neutral pion rest mass. The aim is to showcase how these advanced methods can enhance the quality of event reconstruction.

Sarasty Segura, Carlos Eduardo↗
NASA NTRS1982

Imaging antenna arrays

Many millimeter and far-infrared imaging systems are limited in sensitivity and speed because they depend on a single scanned element. Because of recent advances in planar detectors such as Schottky diodes, superconducting tunnel junctions, and microbolometers, an attractive approach to this problem is a planar antenna array with integrated detectors. A planar line antenna array and optical system for imaging has been developed. The significant advances are a 'reverse-microscope' optical configuration and a modified bow-tie antenna design. In the 'reverse-microscope' configuration, a lens is attached to the bottom of the substrate containing the antennas. Imaging is done through the substrate. This configuration eliminates the troublesome effects of substrate surface waves. The substrate lens has only a single refracting surface, making possible a virtually aplanatic system, with little spherical aberration or coma. The array is characterized by an optical transfer function that is easily measured. An array with 19 dB crosstalk levels between adjacent antennas has been tested and it was found that the array captured 50 percent of the available power. This imaging system was diffraction limited.

Rutledge, D. B.↗
NASA NTRS1987

Dual-Energy X-Radiography With Gadolinium Filter

Image resolution increased, and cost reduced. Proposed dual-energy x-ray imaging system, continuous bremsstrahlung spectrum from x-ray tube filtered by foil of nonradioactive gadolinium or another rare-earth metal to form two-peaked energy spectrum. After passing through patient or object under examination, filtered radiation detected by array of energy-discriminating, photon-counting detectors. Detector outputs processed to form x-ray image for each peak and possibly enhanced image based on data taken at both peaks.

Rutt, Brian↗
NASA NTRS1980

High resolution image measurements of nuclear tracks

The striking clarity and high contrast of the mouths of tracks etched in CR-39 plastic detectors allow automatic measurement of track parameters to be made with simple image-recognition equipment. Using a commercially available Vidicon camera system with a microprocessor-controlled digitizer, resolution for normally incident C-12 and N-14 ions at 32 MeV/amu equivalent to a 14sigma separation of adjacent charges was demonstrated.

Shirk, E. K.↗
NASA NTRS1987

Charge-coupled-device X-ray detector performance model

A model that predicts the performance characteristics of CCD detectors being developed for use in X-ray imaging is presented. The model accounts for the interactions of both X-rays and charged particles with the CCD and simulates the transport and loss of charge in the detector. Predicted performance parameters include detective and net quantum efficiencies, split-event probability, and a parameter characterizing the effective thickness presented by the detector to cosmic-ray protons. The predicted performance of two CCDs of different epitaxial layer thicknesses is compared. The model predicts that in each device incomplete recovery of the charge liberated by a photon of energy between 0.1 and 10 keV is very likely to be accompanied by charge splitting between adjacent pixels. The implications of the model predictions for CCD data processing algorithms are briefly discussed.

Bautz, M. W.↗