Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “light field imaging”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Laser Light Scattering by Shock Waves

Scattering of coherent light as it propagates parallel to a shock wave, formed in front of a bluff cylindrical body placed in a supersonic stream, is studied experimentally and numerically. Two incident optical fields are considered. First, a large diameter collimated beam is allowed to pass through the shock containing flow. The light intensity distribution in the resultant shadowgraph image, measured by a low light CCD camera, shows well-defined fringes upstream and downstream of the shadow cast by the shock. In the second situation, a narrow laser beam is brought to a grazing incidence on the shock and the scattered light, which appears as a diverging sheet from the point of interaction, is visualized and measured on a screen placed normal to the laser path. Experiments are conducted on shocks formed at various free-stream Mach numbers, M, and total pressures, P(sub 0). It is found that the widths of the shock shadows in a shadowgraph image become independent of M and P(sub 0) when plotted against the jump in the refractive index, (Delta)n, created across the shock. The total scattered light measured from the narrow laser beam and shock interaction also follows the same trend. In the numerical part of the study, the shock is assumed to be a 'phase object', which introduces phase difference between the upstream and downstream propagating parts of the light disturbances. For a given shape and (Delta)n of the bow shock the phase and amplitude modulations are first calculated by ray tracing. The wave front is then propagated to the screen using the Fresnet diffraction equation. The calculated intensity distribution, for both of the incident optical fields, shows good agreement with the experimental data.

Panda, J.↗
DOE OSTI2026

The ABCs of phase retrieval: Connecting the acronyms of scanning transmission electron microscopy

High-resolution scanning transmission electron microscopy (S/TEM) is an indispensable tool for characterizing the structure and properties of materials down to the atomic scale. Conventional S/TEM imaging, however, is limited by the phase problem, whereby the phase of the electron exit wave is lost upon detection. Recent advances in diffractive imaging and 4D-STEM have enabled a range of phase-retrieval techniques that computationally reconstruct the missing information encoded in the phase of the transmission function. These approaches offer improved dose efficiency and enhanced sensitivity to weakly scattering signals, extending quantitative imaging to beam-sensitive materials composed of light elements. In this work, we introduce the phase problem in electron microscopy and survey the diverse landscape of phase-retrieval techniques used in the field. Despite their many acronyms and algorithmic variations, these techniques share a common physical and mathematical foundation. We present a unified framework that connects these seemingly distinct methods, from parallax imaging and tilt-corrected bright-field (tcBF-STEM), to aberration-corrected bright-field (acBF-STEM), optimum bright-field (OBF-STEM) and single-sideband (SSB) ptychography, as well as first-moment integrated center of mass techniques (iCOM) and iterative ptychographic algorithms. Based on these insights, we discuss the opportunities and practical limitations of applying these methods across different materials systems, detector designs, and microscope configurations.Graphical abstractRepresentative electron microscopy configurations used for phase retrieval and diffractive imaging in S/TEM: (a) Zernike phase-contrast transmission electron microscopy (TEM), (b) small-convergence-angle four-dimensional scanning transmission electron microscopy (4D-STEM) for nanobeam-based phase reconstruction methods, and (c) large-convergence-angle 4D-STEM for ptychographic and related diffractive imaging techniques reviewed in this work.

36 MATERIALS SCIENCE↗
NASA NTRS2020

Confirmation of the Stellar Binary Microlensing Event, Macho 97-BLG-28

The high-magnification microlensing event MACHO-97-BLG-28 was previously determined to be a binary system composed of either two M dwarfs or an M dwarf and a brown dwarf. We present a revised light-curve model using additional data from the Mt. Stromlo 74″telescope, model estimates of stellar limb darkening, and fitting of the blend separately for each telescope and passband. We find a lensing system with a larger mass ratio, q=0.28±0.01, and smaller projected separation, s=0.61±0.01, than those presented in the original study. We revise the estimate of the lens–source relative proper motion to μ(rel)=2.8±0.5 mas/yr, which indicates that 16.07 yr after the event maximum the lens and source should have separated by 46±8 mas. We revise the radius of the source star using more recent reddening maps and angular diameter–color relations to R(*)=(10.3±1.9) R(ʘ). K- and J-band adaptive optics images of the field taken at this epoch using the NIRC2 imager on the Keck telescope show that the source and lens are still blended, consistent with our light-curve model. With no statistically significant excess flux detection we constrain the mass, M(L)=0.24 (+0.28, -0.12) M(ʘ), and distance, D(L)=7.0±1.0 kpc, of the lensing system. This supports the interpretation of this event as a stellar binary in the Galactic bulge. This lens mass gives a companion mass of M= 0.07(+0.08,-0.04) M(ʘ), close to the boundary between being a star and a brown dwarf.

W. Blackman↗
NASA NTRS1973

The facsimile camera - Its potential as a planetary lander imaging system

The facsimile camera is an optical-mechanical scanning device which is an attractive candidate for planetary lander imaging systems and has been selected for the Viking/Mars mission because of its light weight, small size, and low power requirement. Other advantages are that it can provide good radiometric and photogrammetric accuracy because the complete field of view is scanned with a single photodetector located on or near the optical axis of the objective lens. In addition, this device has the potential capability of multispectral imaging and spectrometric measurements.

Huck, F. O.↗
DOE OSTI2020

Atomic Resolution Imaging of Light Elements in a Crystalline Environment using Dynamic Hollow-Cone Illumination Transmission Electron Microscopy

Multiple electron scattering and the nonintuitive nature of image formation with coherent radiation complicate the interpretation of conventional transmission electron microscopy images. Precession of the illuminating beam in transmission electron microscopy (TEM) can lead to more robust and interpretable images with some penalty to image contrast, a technique known as dynamic hollow-cone illumination TEM. Here, we demonstrate direct and robust imaging of light and heavy atoms in a crystalline environment with this technique. This method is similar to the annular bright-field technique in scanning transmission electron microscopy, via the principle of reciprocity. Dynamic hollow-cone illumination TEM is challenging in practice due to sensitivity to the misalignment of the precession axis, microscope objective aperture, and crystal zone axis.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1983

Fiber optics for astronomical spectroscopy - The Medusa Spectrograph

An instrument has been built to obtain simultaneous spectra of 32 objects in the field of view of the Steward Observatory 2.3 m telescope. Short lengths of optical fiber are used to bring light from galaxy images at the focus of the telescope into a line at the spectrograph slit. This multi-fiber aperture plate instrument has been dubbed the Medusa Spectrograph. The Medusa is now producing spectra of about 100 galaxies per clear night. An optimized version of the instrument called the MX Spectrometer is being constructed to record spectra at a higher rate. This new instrument will have remotely positioned fibers under computer control. A Charge Coupled Device will be used as the spectrograph detector to allow sky subtraction, give increased dynamic range and provide more accurate wavelength calibration. Transmission characteristics of some commercial fibers are discussed, and the microlens optics used to match the telescope and the spectrograph to the fibers to avoid focal ratio degradation are described.

Hill, J. M.↗
NASA NTRS2011

Does Vesta Have Moons?: Dawn's Search for Satellites

Upon approach to asteroid 4 Vesta, the Dawn mission included a dedicated satellite search observation of the operational sphere of the spacecraft around Vesta. Discovery of moons of Vesta would constrain theories of satellite f()rmation. The sequence using the framing camera and clear filter includes three mosaics of six stations acquired on July 9-10. 2011. Each station consists of four sets with three different exposures, 1.5,20 and 270 s. We also processed and scanned the optical navigation sequences until Vesta filled the field of view. Analysis of images involves looking for moving objects in the mosaics and identifying catalogued stars, subtracting them from the image and examining residual objects for evidence of bodies in orbit around Vesta. Celestial coordinates were determined using Astrometry.net, an astrometry calibration service (http://astrometry.net/use.html). We processed the images by subtracting dark and bias fields and dividing by a Hatfield. Images were further filtered subtracting a box car filter (9x9 average) to remove effects of scattered light from Vesta itself. Images were scanned by eye for evidence of motion in directions different from the background stars. All objects were compared with Hubble Space Telescope's Guide Star Catalogue and US Naval Observatory's UCAC3 catalog. We report findings from these observations and analysis, including limits of magnitude, size and motion of objects in orbit around Vesta. We gratefully acknowledge modifications made to Astrometrica http://www.astrometrica.at/ for purposes of this effort.

McFadden, L. A.↗
NASA NTRS2014

Performance Characterization of the Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) CCD Cameras

The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) is a sounding rocket instrument currently being developed by NASA's Marshall Space Flight Center (MSFC), the National Astronomical Observatory of Japan (NAOJ), and other partners. The goal of this instrument is to observe and detect the Hanle effect in the scattered Lyman-Alpha UV (121.6nm) light emitted by the Sun's chromosphere. The polarized spectrum imaged by the CCD cameras will capture information about the local magnetic field, allowing for measurements of magnetic strength and structure. In order to make accurate measurements of this effect, the performance characteristics of the three on- board charge-coupled devices (CCDs) must meet certain requirements. These characteristics include: quantum efficiency, gain, dark current, read noise, and linearity. Each of these must meet predetermined requirements in order to achieve satisfactory performance for the mission. The cameras must be able to operate with a gain of 2.0+/- 0.5 e--/DN, a read noise level less than 25e-, a dark current level which is less than 10e-/pixel/s, and a residual non- linearity of less than 1%. Determining these characteristics involves performing a series of tests with each of the cameras in a high vacuum environment. Here we present the methods and results of each of these performance tests for the CLASP flight cameras.

solar↗
NASA NTRS2017

Comparison of the Coronal Mass Ejection Shock Acceleration of Three Widespread SEP Events During Solar Cycle 24

We studied three solar energetic particle (SEP) events observed on 14 August 2010, 3 November 2011, and 5 March 2013 by Solar Terrestrial Relations Observatory (STEREO) A, B, and near-Earth (L1) spacecraft with a longitudinal distribution of particles greater than 90 degrees. Using a forward modeling method combined with extreme ultraviolet and white-light images, we determined the angular extent of the shock, the time and location (cobpoint) of the shock intersection with the magnetic field line connecting to each spacecraft, and compute the shock speed at the cobpoint of each spacecraft. We then examine whether the observations of SEPs at each spacecraft were accelerated and injected by the spatially extended shocks or whether another mechanism such as cross-field transport is required for an alternative explanation. Our analyses results indicate that the SEPs observed at the three spacecraft on 3 November, STEREO B (STB) and L1 on 14 August, and the 5 March SEP event at STEREO A (STA) can be explained by the direct shock acceleration. This is consistent with the observed significant anisotropies, short time delays between particle release times and magnetic connection times, and sharp rises in the SEP time profiles. Cross-field diffusion is the likely cause for the 14 August SEP event observed by STA and the 5 March SEPs observed by STB and L1 spacecraft, as particle observations featured weak electron anisotropies and slow rising intensity profiles. Otherwise, the wide longitudinal spread of these SEP increases would require an existence of a circumsolar shock, which may not be a correct assumption in the corona and heliosphere.

Xie, H.↗
NASA NTRS1995

Hubble Space Telescope Images of Nearby Luminous Quasars: Results for Eight Quasars and Tests of the Detection Sensitivity - 2

Observations with the Wide-Field Camera of the Hubble Space Telescope (HST) are presented for eight intrinsically luminous quasars with redshifts between 0.16 and 0.29. These observations, when combined with a similar HST study of the quasar PKS 2349-014, show that luminous nearby quasars exist in a variety of environments. Seven companion galaxies brighter than M(V) = 16.5 (H(sub 0) = 100 km s(sup -1) Mpc(sup -1), Omega(sub 0) = 1.0) lie within a projected distance of 25 kpc of the quasars; three of the companions are located closer than 3'' (6 kpc projected distance) from the quasars, well within the volume that would be enclosed by a typical L* host galaxy. The observed association of quasars and companion galaxies is statistically significant and may he an important element in the luminous-quasar phenomenon. Apparent host galaxies are detected for three of the quasars: PG 1116+215, 3C 273, and PG 1444+407; the hosts have an average absolute magnitude of about 0.6 mag brighter than L*. The agreement between the previously published major-axis directions in ground-based images and in the present HST images of 3C 273 and PG 1444+407 constitutes important evidence supporting the reality of these candidate host galaxies. Upper limits are placed on the visual-band brightnesses of representative galactic hosts for all the quasars. These limits are established by placing galaxy images obtained with HST underneath the quasars and measuring at what faintness level the known galaxies are detected. On average, the HST spirals would have been detected if they were as faint as 1 mag below L*, and the early-type galaxies could have been detected down to a brightness level of about L*, where L* is the Schechter characteristic luminosity of field galaxies. Smooth, featureless galaxy models (exponential disks or de Vaucouleurs profiles) are fitted to the residual light after a best-fitting point source is subtracted from the quasar images. The results show that smooth spiral galaxies brighter than, on average, about L*, would have been detected. These upper limits, or possible detections, are consistent with, for example, the eight luminous quasars studied in this paper, occurring in host galaxies that have a Shechter luminosity function with a lower cutoff in the range 0.01-0.1 L*. Tests are performed to determine if our failure to detect, in some cases, luminous host galaxies could be an artifact caused by our analysis procedures. These tests include comparing the measured point-spread function (PSF) for our HST observations with the PSFs used in previous ground-based studies of host galaxies, measuring the fluctuations in the sky signals that were subtracted from the quasar images, evaluating empirically the effects of using different stellar PSFs in the analysis, carrying out the subtraction of the stellar (nuclear) source in different ways, creating and analyzing artificial active galactic nuclei (AGNs) with known surface brightnesses, and fitting the observed quasar light to an analytic model that includes a host galaxy.

Bahcall, John N.↗
NASA NTRS2001

Two-photon interferometry for high-resolution imaging

We discuss advantages of using non-classical states of light for two aspects of optical imaging: creating of miniature images on photosensitive substrates, which constitutes the foundation for optical lithography, and conversely, imaging of micro objects. In both cases, the classical resolution limit given by the Rayleigh criterion is approximately a half of the optical wavelength. It has been shown, however, that by using multi-photon quantum states of the light field, and multi-photon sensitive material or detector, this limit can be surpassed. In the present work, we give a rigorous quantum mechanical treatment of this problem, address some particularly widespread misconceptions and discuss the requirements arising on the way of turning the research on quantum imaging into a practical technology.

quantum technology↗
NASA NTRS2012

Variable Sampling Mapping

The performance of an optical system (for example, a telescope) is limited by the misalignments and manufacturing imperfections of the optical elements in the system. The impact of these misalignments and imperfections can be quantified by the phase variations imparted on light traveling through the system. Phase retrieval is a methodology for determining these variations. Phase retrieval uses images taken with the optical system and using a light source of known shape and characteristics. Unlike interferometric methods, which require an optical reference for comparison, and unlike Shack-Hartmann wavefront sensors that require special optical hardware at the optical system's exit pupil, phase retrieval is an in situ, image-based method for determining the phase variations of light at the system s exit pupil. Phase retrieval can be used both as an optical metrology tool (during fabrication of optical surfaces and assembly of optical systems) and as a sensor used in active, closed-loop control of an optical system, to optimize performance. One class of phase-retrieval algorithms is the iterative transform algorithm (ITA). ITAs estimate the phase variations by iteratively enforcing known constraints in the exit pupil and at the detector, determined from modeled or measured data. The Variable Sampling Mapping (VSM) technique is a new method for enforcing these constraints in ITAs. VSM is an open framework for addressing a wide range of issues that have previously been considered detrimental to high-accuracy phase retrieval, including undersampled images, broadband illumination, images taken at or near best focus, chromatic aberrations, jitter or vibration of the optical system or detector, and dead or noisy detector pixels. The VSM is a model-to-data mapping procedure. In VSM, fully sampled electric fields at multiple wavelengths are modeled inside the phase-retrieval algorithm, and then these fields are mapped to intensities on the light detector, using the properties of the detector and optical system, for comparison with measured data. Ultimately, this model-to-data mapping procedure enables a more robust and accurate way of incorporating the exit-pupil and image detector constraints, which are fundamental to the general class of ITA phase retrieval algorithms.

Smith, Jeffrey, S.↗
DOE OSTI2024

Photoinduced patterning of oxygen vacancies to promote the ferroelectric phase of Hf 0.5 Zr 0.5 O 2

Photoinduced reductions in the oxygen vacancy concentration were leveraged to increase the ferroelectric phase fraction of Hf 0.5 Zr 0.5 O 2 thinfilms. Modest ( ~ 2 — 77 pJ=cm 2 ) laser doses of visible light (488 nm, 2.54 eV) spatially patterned the concentration of oxygen vacancies as monitored by photoluminescence imaging. Local, tip-based, near-field, nanoFTIR measurements showed that the photoinduced oxygen vacancy concentration reduction promoted formation of the ferroelectric phase (space group Pca2 1 ), resulting in an increase in the piezoelectric response measured by piezoresponse force microscopy. Photoinduced vacancy tailoring provides, therefore, a spatially prescriptive, postsynthesis, and low-entry method to modify phase in HfO 2 -based materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Enhanced imaging of electronic hot spots using quantum squeezed light

Detecting electronic hot spots is important for understanding the heat dissipation and thermal management of electronic and semiconductor devices. Optical thermoreflective imaging is being used to perform precise temporal and spatial imaging of heat on wires and semiconductor materials. We apply quantum squeezed light to perform thermoreflective imaging on micro-wires, surpassing the shot-noise limit of classical approaches. We obtain a far-field temperature sensing accuracy of 42 mK after 50 ms of averaging and show that a 256×256 pixel image can be constructed with such sensitivity in 10 min. We can further obtain single-shot temperature sensing of 1.6 K after only 10 μs of averaging, enabling a dynamical study of heat dissipation. Not only do the quantum images provide accurate spatiotemporal information about heat distribution but also the measure of quantum correlation provides additional information, inaccessible by classical techniques, which can lead to a better understanding of the dynamics. We apply the technique to both aluminum and niobium microwires and discuss the applications of the technique in studying electron dynamics at low temperatures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Phase-contrast 3D tomography of HeLa cells grown in PLLA polymer electrospun scaffolds using synchrotron X-rays

Advanced imaging is useful for understanding the three-dimensional (3D) growth of cells. X-ray tomography serves as a powerful noninvasive, nondestructive technique that can fulfill these purposes by providing information about cell growth within 3D platforms. There are a limited number of studies taking advantage of synchrotron X-rays, which provides a large field of view and suitable resolution to image cells within specific biomaterials. In this study, X-ray synchrotron radiation microtomography at Diamond Light Source and advanced image processing were used to investigate cellular infiltration of HeLa cells within poly L-lactide (PLLA) scaffolds. This study demonstrates that synchrotron X-rays using phase contrast is a useful method to understand the 3D growth of cells in PLLA electrospun scaffolds. Two different fiber diameter (2 and 4 µm) scaffolds with different pore sizes, grown over 2, 5 and 8 days in vitro , were examined for infiltration and cell connectivity. After performing visualization by segmentation of the cells from the fibers, the results clearly show deeper cell growth and higher cellular interconnectivity in the 4 µm fiber diameter scaffold. Finally, this indicates the potential for using such 3D technology to study cell–scaffold interactions for future medical use.

3D culture↗
DOE OSTI2021

Outbursting Young Stellar Object PGIR 20dci in the Perseus Arm

We report the discovery of a likely outbursting Class I young stellar object, associated with the star-forming region NGC 281-W (distance ~2.8 kpc). The source is currently seen only at infrared wavelengths, appearing in both the Palomar Gattini InfraRed (1.2 μm) and the Near-Earth Object Wide-field Infrared Survey Explorer (3.4 and 4.6 μm) photometric time-domain surveys. Recent near-infrared imaging reveals a new, extended scattered light nebula. Recent near-infrared spectroscopy confirms the similarity of PGIR 20dci to FU Ori–type sources, based on strong molecular absorption in CO, H{sub 2}O, and OH; weak absorption in several atomic lines; and a warm wind/outflow as indicated by a P Cygni profile in the He i λ10830 line. This is a rare case of an FU Ori star with a well-measured long-term photometric rise before a sharper outburst, and the second instance of an FU Ori star with a documented two-step brightening in the mid-infrared.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS1984

The problem of atmospheric turbulence

All ground-based observations of the solar five-minute oscillations are affected by turbulence in the Earth's atmosphere that leads to substantial refractive index variations. The turbulent motions serve to mix an air mass that is thermally stratified in the vertical, thereby producing intermittent thermal fluctuations over a wide range of heights in the atmosphere. These thermal structures yield refractive index changes that deflect the light path in a complicated way, producing intricate variations of amplitude and phase in what might have started out as simple plane waves. Since the fluid turbulence is statistical in nature, so too is the optical turbulence which is an integral measure of the refractive index changes along the light travel path. All of this produces what is usually called atmospheric seeing, which consists of image motion, blurring and distortion across the field of view. The effects of atmospheric seeing upon observations of five-minute oscillations carried out from the ground were assessed. This will help to provide a baseline estimate of the scienctific benefits that might accrue if one were able to observe the same oscillations from a space observatory unfettered by seeing effects.

Toomre, J.↗
NASA NTRS1992

The Ultraviolet Imaging Telescope - Design and performance

The instrumental configuration, calibration, and operations during the first flight of the Ultraviolet Imaging Telescope on the Astro-1 mission, December 2-10, 1990, are described. The UV images of a wide variety of astronomical objects were recorded with a 40-arcmin diameter field of view. Images of targets as faint as magnitude 21 (UV) were secured with a resolution of about 3 arcsec. The optics, light baffling, and image motion compensation system are summarized, and detectors and electronic subsystems are described.

Stecher, Theodore P.↗