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At least 991 records · Page 55
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Time-reversed Young’s experiment: Deterministic, diffractionless second-order interference effect

The classic Young’s double-slit experiment exhibits first-order interference, producing alternating bright and dark fringes shaped by the diffraction effect of the slits. In contrast, here we demonstrate that its time-reversed configuration generates an ideal, deterministic second-order ‘ghost’ interference pattern free from diffraction and first-order effects with the use of only a position-fixed detector. The pattern’s size is governed by the dimensions of the ‘effectively extended light source’ formed by point emitter(s). Beyond highlighting the nonreciprocal physics between the two configurations, this system unlocks a range of novel phenomena inaccessible in traditional double-slit experiments. These include fully programmable, digitized interference fringe formations and the ability to align the pattern plane with the source plane on the same side of the setup. Remarkably, our proposed experiment achieves these outcomes without relying on nonclassical correlations or quantum entanglement. Here, by restoring time-reversal symmetry and eliminating diffraction, our theoretical analysis reveals that this approach offers exciting potential for advancing optical imaging and sensing technologies with improved transverse and longitudinal phase-shift sensitivity and resolution limit beyond current limitations.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS1989

Geometrical optics design of a compact range Gregorian subreflector system by the principle of the central ray

In recent years, the compact range has become very popular for measuring Radar Cross Section (RCS) and antenna patterns. The compact range, in fact, offers several advantages due to reduced size, a controlled environment, and privacy. On the other hand, it has some problems of its own, which must be solved properly in order to achieve high quality measurement results. For example, diffraction from the edges of the main reflector corrupts the plane wave in the target zone and creates spurious scattering centers in RCS measurements. While diffraction can be minimized by using rolled edges, the field of an offset single reflector compact range is corrupted by three other errors: the taper of the reflected field, the cross polarization introduced by the tilt of the feed and the aperture blockage introduced by the feed itself. These three errors can be eliminated by the use of a subreflector system. A properly designed subreflector system offers very little aperture blockage, no cross-polarization introduced and a minimization of the taper of the reflected field. A Gregorian configuration has been adopted in order to enclose the feed and the ellipsoidal subreflector in a lower chamber, which is isolated by absorbers from the upper chamber, where the main parabolic reflector and the target zone are enclosed. The coupling between the two rooms is performed through a coupling aperture. The first cut design for such a subreflector system is performed through Geometrical Optics ray tracing techniques (GO), and is greatly simplified by the use of the concept of the central ray introduced by Dragone. The purpose of the GO design is to establish the basic dimensions of the main reflector and subreflector, the size of the primary and secondary illuminating surfaces, the tilt angles of the subreflector and feed, and estimate the feed beamwidth. At the same time, the shape of the coupling aperture is initially determined.

Clerici, Giancarlo↗
DOE OSTI2021

Fast and Scalable Synthesis of LiNi 0.5 Mn 1.5 O 4 Cathode by Sol–Gel-Assisted Microwave Sintering

High-voltage spinel LiNi 0.5 Mn 1.5 O 4 (LNMO) is a promising cathode material for high-energy-density and high-power-density lithium-ion batteries (LIBs). The high cost of the currently available LIBs needs to be addressed urgently for wide application in the transport sector (electric vehicles, buses) and large-scale energy storage systems (ESS). Of significance, herein, novel fast and scalable microwave-assisted synthesis of LNMO is reported, which leads to a production cost cut. X-ray diffraction (XRD) analysis confirms the formation of the desired phase with high crystallinity. Field emission scanning (FE-SEM) and transmission electron microscopy (TEM) analyses indicate that the synthesized phase is of nanometric size (50–150 nm) due to an extremely short sintering time (20 min). The material synthesized at 750 °C shows a higher initial discharge capacity (130 mA h g -1 ) than that synthesized at 650 °C (115 mA h g -1 ). The materials heat treated at higher temperatures show better electrochemical performance in terms of initial capacity, rate capability, and improved cycling. The improved electrochemical performance of LNMO at 750 °C is attributed to the formation of a stable crystal structure, low charge transfer resistance at the electrode/electrolyte interface, high electrical conductivity due to the presence of a disorder structure, and improved ionic diffusivity.

25 ENERGY STORAGE↗
DOE OSTI2026

A compact in situ polarized 3He neutron spin filter for the diffractometer VULCAN at the Spallation Neutron Source

We have built and commissioned a compact in situ 3He polarizer based on spin-exchange optical pumping for the engineering materials diffractometer, named VULCAN, at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory. The system achieved 78% 3He polarization with a short pump-up time constant of 2.2 h. Its first deployment in an in situ half-polarized neutron diffraction experiment on a magnetic shape memory alloy, Ni–Mn–Ga, revealed changes in magnetization coupled to deformation twinning under compression. With this new capability, VULCAN has become the first diffractometer at SNS capable of performing polarized neutron experiments, opening new opportunities to study a wider range of magnetism-related material behaviors under varied thermal, mechanical, electrical, and/or magnetic fields.

Fu, Sichao [ORNL] (ORCID:0009000846771640)↗
DOE OSTI2026

Machine learning-based interatomic potential development and phase transition analysis of ferroelectric hafnium dioxide

The ferroelectric phase (𝑃⁢𝑐⁢𝑎⁢2 1 , which is in orthorhombic symmetry) of hafnium dioxide (HfO 2 ) has gained much attention due to its potential applications in nanoelectronics and advanced memory devices. However, its complex phase behavior under external stimuli, such as pressure and temperature, remains a subject of intense investigation. This study focuses on developing a machine learning-based interatomic potential (MLIP) that is trained with data from density-functional theory (DFT) calculations to simulate phase transitions and mechanical properties of HfO 2 . The developed MLIP predicts lattice parameters, equations of state, bulk and shear moduli, and elastic constants that closely align with DFT predictions for several phases and at various pressures. Once validated, the MLIP is used to investigate the phase transitions of ferroelectric HfO 2 (𝑃⁢𝑐⁢𝑎⁢2 1 ) under both isobaric and constant stress conditions at elevated temperatures ranging from 200 to 2500 K. We used several complementary methods, including local symmetry identification, radial distribution function, and x-ray diffraction characterization, to identify interesting phase transitions among several competitive hafnia phases predicted from our simulations. The suggested methods uniformly reveal that under pure deviatoric condition, the system favors a transition from the orthorhombic 𝑃⁢𝑐⁢𝑎⁢2 1 phase to a tetragonal (𝑃⁢4 2 /𝑛⁢𝑚⁢𝑐) phase, whereas a zero stress condition drives the system from the 𝑃⁢𝑐⁢𝑎⁢2 1 phase to another orthorhombic (𝑃⁢𝑏⁢𝑐⁢𝑛) phase. These findings provide crucial insights into stress and temperature-induced phase behavior of hafnia, guiding future experimental and theoretical studies for optimizing hafnia-based ferroelectric devices.

Ferroelectric HfO2↗
DOE OSTI2021

Disentangling x-ray dichroism and birefringence via high-purity polarimetry

High-brilliance synchrotron radiation sources have opened new avenues for x-ray polarization analysis that go far beyond conventional polarimetry in the optical domain. With linear x-ray polarizers in a crossed setting, polarization extinction ratios down to 10 -10 can be achieved. This renders the method sensitive to probe the tiniest optical anisotropies that would occur, for example, in strong-field quantum electrodynamics due to vacuum birefringence and dichroism. Here we show that high-purity polarimetry can be employed to reveal electronic anisotropies in condensed matter systems with utmost sensitivity and spectral resolution. Taking CuO and La 2 CuO 4 as benchmark systems, we present a full characterization of the polarization changes across the Cu K-absorption edge and their separation into dichroic and birefringent contributions. At diffraction-limited synchrotron radiation sources and x-ray lasers, where polarization extinction ratios of 10 -12 can be achieved, our method has the potential to assess birefringence and dichroism of the quantum vacuum in extreme electromagnetic fields.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Process–Property–Performance Mapping of Additively Manufactured 316H Stainless Steel Components

The Advanced Materials and Manufacturing Technologies Program is focused on accelerating the development of advanced materials and components fabricated via additive manufacturing, and is using laser powder bed fusion (LPBF) of 316H stainless steel as an initial case study. In the previous fiscal year, miniature high-throughput specimens were printed on multiple LPBF systems to provide initial processing windows to minimize porosity and limit epitaxial grain growth during prints. This fiscal year, scaled builds were completed on three different LPBF systems at ORNL: a GE Concept Laser M2, a Renishaw AM400, and an EOS M290. Builds on the Concept Laser were conducted on multiple powder lots and processing parameter ranges to provide microstructure effects on time-independent and time-dependent mechanical properties. Builds on the Renishaw were produced using Oak Ridge National Laboratory (ORNL)-optimized printing parameters and Argonne National Laboratory (ANL)-optimized printing parameters to compare outcomes of parallel process optimization efforts at different national laboratories on the same LPBF system. Similarly, the build completed on the EOS M290 replicated the processing parameters of builds completed at Los Alamos National Laboratory (LANL). Optical microscopy and electron backscatter diffraction characterization was completed on all builds. In addition to the general round robin characterization, this work-package generated time-independent data, including tensile and fracture toughness test data on scaled Concept Laser builds as a function of processing parameters and post-build heat treatment. This analysis is complimentary to work in parallel work packages aiming to establish heat treatment and processing effects on time-dependent properties. It was found that although the stress-relief heat treatment provides the highest strength at lower-temperatures, tensile strength begins to converge at higher temperatures regardless of heat treatment condition. In addition, the more rigorous solution annealing and hot-isostatic pressing post-build heat treatments result in higher fracture toughness than the stress-relieved condition. The root-causes of the lower fracture toughness of the stress-relieved LPBF 316H material was informed via a stress-relief optimization study on a scaled concept laser print, where it was found that although dislocation recovery was largely complete after only a couple hours at 650°C, the extended hold of the current 24h heat treatment employed on scaled builds likely caused increased carbide volume fractions along the LPBF 316H grain boundaries, thereby deteriorating crack propagation resistance. This trend was seen to become more deleterious with additional increases of stress-relief temperature to 750°C or 850°C. These results have helped inform a new optimal stress-relief annealing condition for LPBF 316H for future campaign testing (650°C for 2h).

36 MATERIALS SCIENCE↗
DOE OSTI2024

Process–Property–Performance Mapping of Additively Manufactured 316H Stainless Steel Components

The Advanced Materials and Manufacturing Technologies Program is focused on accelerating the development of advanced materials and components fabricated via additive manufacturing, and is using laser powder bed fusion (LPBF) of 316H stainless steel as an initial case study. In the previous fiscal year, miniature high-throughput specimens were printed on multiple LPBF systems to provide initial processing windows to minimize porosity and limit epitaxial grain growth during prints. This fiscal year, scaled builds were completed on three different LPBF systems at ORNL: a GE Concept Laser M2, a Renishaw AM400, and an EOS M290. Builds on the Concept Laser were conducted on multiple powder lots and processing parameter ranges to provide microstructure effects on time-independent and time-dependent mechanical properties. Builds on the Renishaw were produced using Oak Ridge National Laboratory (ORNL)-optimized printing parameters and Argonne National Laboratory (ANL)-optimized printing parameters to compare outcomes of parallel process optimization efforts at different national laboratories on the same LPBF system. Similarly, the build completed on the EOS M290 replicated the processing parameters of builds completed at Los Alamos National Laboratory (LANL). Optical microscopy and electron backscatter diffraction characterization was completed on all builds. In addition to the general round robin characterization, this work-package generated time-independent data, including tensile and fracture toughness test data on scaled Concept Laser builds as a function of processing parameters and post-build heat treatment. This analysis is complimentary to work in parallel work packages aiming to establish heat treatment and processing effects on time-dependent properties. It was found that although the stress-relief heat treatment provides the highest strength at lower-temperatures, tensile strength begins to converge at higher temperatures regardless of heat treatment condition. In addition, the more rigorous solution annealing and hot-isostatic pressing post-build heat treatments result in higher fracture toughness than the stress-relieved condition. The root-causes of the lower fracture toughness of the stress-relieved LPBF 316H material was informed via a stress-relief optimization study on a scaled concept laser print, where it was found that although dislocation recovery was largely complete after only a couple hours at 650°C, the extended hold of the current 24h heat treatment employed on scaled builds likely caused increased carbide volume fractions along the LPBF 316H grain boundaries, thereby deteriorating crack propagation resistance. This trend was seen to become more deleterious with additional increases of stress-relief temperature to 750°C or 850°C. These results have helped inform a new optimal stress-relief annealing condition for LPBF 316H for future campaign testing (650°C for 2h).

36 MATERIALS SCIENCE↗
DOE OSTI2022

Nematic Fluctuations in the Non-Superconducting Iron Pnictide BaFe 1.9-x Ni 0.1 Cr x As 2

The main driven force of the electronic nematic phase in iron-based superconductors is still under debate. Here, we report a comprehensive study on the nematic fluctuations in a non-superconducting iron pnictide system BaFe 1.9-x Ni 0.1 Cr x As 2 by electronic transport, angle-resolved photoemission spectroscopy (ARPES), and inelastic neutron scattering (INS) measurements. Previous neutron diffraction and transport measurements suggested that the collinear antiferromagnetism persists to x = 0.8, with similar Néel temperature TN and structural transition temperature Ts around 32 K, but the charge carriers change from electron type to hole type around x = 0.5. In this study, we have found that the in-plane resistivity anisotropy also highly depends on the Cr dopings and the type of charge carriers. While ARPES measurements suggest possibly weak orbital anisotropy onset near Ts for both x = 0.05 and x = 0.5 compounds, INS experiments reveal clearly different onset temperatures of low-energy spin excitation anisotropy, which is likely related to the energy scale of spin nematicity. These results suggest that the interplay between the local spins on Fe atoms and the itinerant electrons on Fermi surfaces is crucial to the nematic fluctuations of iron pnictides, where the orbital degree of freedom may behave differently from the spin degree of freedom, and the transport properties are intimately related to the spin dynamics.

36 MATERIALS SCIENCE↗
NASA NTRS1972

Automated thematic mapping and change detection of ERTS-A images

The author has identified the following significant results. For the exploitation of the ERTS-1 images, both multispectral and spatial pattern recognition techniques are important. A multispectral recognition software program was successfully tested. A technique for the generation of resource boundaries has been successfully combined with terrain recognition software resulting in a regionalized terrain classification system. Digital registration of multispectral images has been achieved. Also, photointerpretation results from one test site are reported and the development of spatial terrain signatures from optical diffraction patterns is described.

Gramenopoulos, N.↗
NASA NTRS1976

Exoelectron emission from a clean, annealed magnesium single crystal during oxygen adsorption

Exoelectron emission was observed from a clean, annealed Mg (0001) surface during oxygen and chlorine adsorption at pressures of 6.5x10 0.00001- N/sq m and lower. the studies were performed in an ultrahigh vacuum system. The crystals were cleaned by argon ion bombardment and annealed at 300 C. Auger electron spectroscopy was used to verify surface cleanliness, and low energy electron diffraction was used to verify that the surface was annealed. The emission was found to be oxygen arrival rate dependent. Two peaks were observed in the electron emission with exposure. Evidence is presented that the formation of the second peak corresponds to oxidation of the Mg surface. No emission was observed from clean aluminum during adsorption. Results verify that electron emission occurs from a strain free surface simply upon adsorption of oxygen. A qualitative explanation for the mechanisms of emission in terms of chemical effects is presented.

Ferrante, J.↗
NASA NTRS1989

Synthesis and thermal properties of strontium and calcium peroxides

A practical synthesis and a discussion of some chemical properties of pure strontium peroxide and calcium peroxide are presented. The general synthesis of these peroxides involves precipitation of their octahydrates by addition of H2O2 to aqueous ammoniacal Sr(NO3)2 or CaCl2. The octahydrates are converted to the anhydrous peroxides by various dehydration techniques. A new x-ray diffraction powder pattern for CaO2 x 8H2O is given from which lattice parameters a=6.212830 and c=11.0090 were calculated on the basis of the tetragonal crystal system.

Philipp, Warren H.↗
NASA NTRS1993

Applications of advanced diffractive optical elements

Digital Optics Corporation is a UNC-Charlotte spin-off company, established to transfer technology developed at UNC-Charlotte for the design and manufacture Computer Generated Holograms (CGH's) and to market products based on CGH technology. DOC acquired core technologies from UNC-Charlotte including: (1) a CGH encoding process that can provide holograms with extremely high diffraction efficiency; (2) a low cost, high precision CGH manufacturing process; and (3) extensive holographic and refractive element design capabilities for design and evaluation of complex optical systems. These technologies have been used to design and/or manufacture optical components for a variety of applications including: (1) generation of Spot arrays; (2) fiber optic coupling elements; (3) optical interconnects between VLSI chips within and between multichip modules; and (4) imaging systems for head-mounted displays (HMD's).

Welch, W. Hudson↗
NASA NTRS1996

Evaluation of Two Computational Techniques of Calculating Multipath Using Global Positioning System Carrier Phase Measurements

Two computational techniques are used to calculate differential phase errors on Global Positioning System (GPS) carrier war phase measurements due to certain multipath-producing objects. The two computational techniques are a rigorous computati electromagnetics technique called Geometric Theory of Diffraction (GTD) and the other is a simple ray tracing method. The GTD technique has been used successfully to predict microwave propagation characteristics by taking into account the dominant multipath components due to reflections and diffractions from scattering structures. The ray tracing technique only solves for reflected signals. The results from the two techniques are compared to GPS differential carrier phase ns taken on the ground using a GPS receiver in the presence of typical International Space Station (ISS) interference structures. The calculations produced using the GTD code compared to the measured results better than the ray tracing technique. The agreement was good, demonstrating that the phase errors due to multipath can be modeled and characterized using the GTD technique and characterized to a lesser fidelity using the DECAT technique. However, some discrepancies were observed. Most of the discrepancies occurred at lower devations and were either due to phase center deviations of the antenna, the background multipath environment, or the receiver itself. Selected measured and predicted differential carrier phase error results are presented and compared. Results indicate that reflections and diffractions caused by the multipath producers, located near the GPS antennas, can produce phase shifts of greater than 10 mm, and as high as 95 mm. It should be noted tl the field test configuration was meant to simulate typical ISS structures, but the two environments are not identical. The GZ and DECAT techniques have been used to calculate phase errors due to multipath o the ISS configuration to quantify the expected attitude determination errors.

Gomez, Susan F.↗
NASA NTRS2007

GISMO

The 2 mm (1 50 GHz) atmospheric window enables unparalleled ground-based observations of the earliest active dusty galaxies in the universe. We have undertaken the development of a bolometer camera, GISMO (the Goddard-IRAM Superconducting 2-Millimeter Observer), which will obtain large and sensitive sky maps at this wavelength. The instrument will be used at the IRAM 30 m telescope, where we hope to have a trial observing run in Spring of 2007. The innovative element in this camera is its 8x1 6 fully sampled planar array of multiplexed superconducting transition edge sensor bolometers. This array is based on our recently demonstrated Backshort Under Grid architecture, designed to be scaled to kilopixel arrays with high sensitivity (of around 4 * 10 (exp -17)/ W* square root of Hz at T(sub c) approximates 450mK). A compact cryogenic optical system provides a wide field of view, (almost 2'x4') enabling GISMO to be very efficient at detecting sources serendipitously in large sky surveys, while retaining diffraction-limited imaging performance. GISMO will provide significantly greater imaging sensitivity and mapping speed at this wavelength than has previously been possible. The major scientific driver for the instrument is to detect dust emission from high-z Ultraluminous Infrared Galaxies (ULIRGs) and quasars. The instrument provides an important portion of the spectrum of high redshift galaxies at the Rayleigh-Jeans part of the dust emission spectrum, even at the highest redshifts. Models of galaxy evolution predict that GISMO will serendipitously detect one galaxy in every four hours of observing blank sky, and that one quarter of these galaxies will be at a redshift of z > 6.5.

Benford, Dominic↗
NASA NTRS2013

Electro-Optic Time-to-Space Converter for Optical Detector Jitter Mitigation

A common problem in optical detection is determining the arrival time of a weak optical pulse that may comprise only one to a few photons. Currently, this problem is solved by using a photodetector to convert the optical signal to an electronic signal. The timing of the electrical signal is used to infer the timing of the optical pulse, but error is introduced by random delay between the absorption of the optical pulse and the creation of the electrical one. To eliminate this error, a time-to-space converter separates a sequence of optical pulses and sends them to different photodetectors, depending on their arrival time. The random delay, called jitter, is at least 20 picoseconds for the best detectors capable of detecting the weakest optical pulses, a single photon, and can be as great as 500 picoseconds. This limits the resolution with which the timing of the optical pulse can be measured. The time-to-space converter overcomes this limitation. Generally, the time-to-space converter imparts a time-dependent momentum shift to the incoming optical pulses, followed by an optical system that separates photons of different momenta. As an example, an electro-optic phase modulator can be used to apply longitudinal momentum changes (frequency changes) that vary in time, followed by an optical spectrometer (such as a diffraction grating), which separates photons with different momenta into different paths and directs them to impinge upon an array of photodetectors. The pulse arrival time is then inferred by measuring which photodetector receives the pulse. The use of a time-to-space converter mitigates detector jitter and improves the resolution with which the timing of an optical pulse is determined. Also, the application of the converter enables the demodulation of a pulse position modulated signal (PPM) at higher bandwidths than using previous photodetector technology. This allows the creation of a receiver for a communication system with high bandwidth and high bits/photon efficiency.

Birnbaum, Kevin↗
NASA NTRS2002

Imaging Forming Planetary Systems: The HST/STIS Legacy and Prospects for Future Missions

The first indication that debris and protoplanetary disks associated with other, young planetary systems were sufficiently nearby to image came with the IRAS detection of infrared excesses around $\beta$ Pic, Vega, Fomalhaut, and $\epsilon$ Eri. Moving beyond analysis of the infrared excess to optical and near-IR imaging requires access to high Strehl ratio and high contrast imaging techniques, with the ability to efficiently reject the residual scattered and diffracted light from the star to reveal the fainter scattered light and circumstellar emission originating from the vicinity of the star. HST/STIS imaging studies have made use of incomplete Lyot coronagraphic imaging modes to reveal the warped, inner disk of $\beta$ Pic, provide the highest spatial resolution images of young debris disk systems such as HR 4796A, have revealed the presence of azimuthally symmetric structure in HD 141569 and HD 163296, and have demonstrated that currently active, collimated outflows survive to higher stellar masses than previously expected, and through more of the star's pre-main sequence lifetime than anticipated. The HST/STIS coronagraphic imaging legacy will be discussed, together with the implications for future NIR and optical high contrast imaging capabilities.

Grady, Carol↗
NASA NTRS1989

Two-dimensional high temperature strain measurement system

Two-dimensional optical strain measurements on high temperature test specimens are presented. This two-dimensional capability is implemented through a rotatable sensitive strain axis. Three components of surface strain can be measured automatically, from which the first and second principal strains are calculated. One- and two-dimensional strain measurements at temperatures beyond 750 C with a resolution of 15 microstrain are demonstrated. The system is based on a one-dimensional speckle shift technique. The speckle shift technique makes use of the linear relationship between surface strain and the differential shift of laser speckle patterns in the diffraction plane. Laser speckle is a phase effect that occurs when spatially coherent light interacts with an optically rough surface. Since speckle is generated by any diffusely reflecting surface, no specimen preparation is needed to obtain a good signal. Testing was done at room temperature on a flat specimen of Inconel 600 mounted in a fatigue testing machine. A load cell measured the stress on the specimen before and after acquiring the speckle data. Strain components were measured at 0 C (parallel to the load axis) and at plus or minus 45 C, and plots indicate the calculated values of the first and second principal strains. The measured values of Young's modulus and Poisson's ratio are in good agreement with handbook values. Good linearity of the principal strain moduli at high temperatures indicate precision and stability of the system. However, a systematic error in the high-temperature test setup introduced a scale factor in the slopes of the two-dimensional stress-strain curves. No high temperature effects, however, have been observed to degrade speckle correlation.

Lant, Christian T.↗