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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 1,243 records · Page 69
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Integrated high-order surface diffraction gratings for diode lasers

High-order surface diffraction gratings acting as a distributed Bragg reflector (DBR) in mesa stripe semiconductor lasers (λ = 1030 nm) have been studied theoretically and experimentally. Higher order interfering radiation modes (IRMs), which propagate off the plane of the waveguide, have been shown to have a crucial effect on the reflection and transmission spectra of the DBR. The decrease in the reflectivity of the DBR in response to the increase in the diffraction efficiency of these modes may reach 80% and more. According to theoretical analysis results, the intensity of the higher order IRMs is determined by the geometry of the DBR groove profile. Experimental data demonstrate that the noncavity modes are responsible for parasitic light leakage losses in the laser cavity. It has been shown that, in the case of nonoptimal geometry of the grating groove profile, the overall external differential quantum efficiency of the parasitic laser emission may exceed 45%, which is more than half of the laser output power. The optimal geometry of the DBR groove profile is trapezoidal, with the smallest possible lower base. Experimental evidence has been presented that this geometry considerably reduces the power of the higher order IRMs and minimises the parasitic light leakage loss. (lasers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Near-field focusing of an optical wave by diffraction gratings

We report the investigation results for spatially-localised light structures (photonic nanojets) under near-field optical radiation scattering on phase diffraction gratings. Main parameters of photonic nanojets from gratings with sawtooth, rectangular and hemispherical groove profiles are obtained by numerical electrodynamic simulation. It is found that by varying a period, degree of filling, groove shape and parameters of optically contrast coating of the diffraction grating one can control the characteristics of the produced photonic jets in a wide range. (laser beams)

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Acousto-optic method of spatial frequency filtration based on diffraction of two eigenmodes of a crystal

A method is proposed for two-dimensional spatial frequency filtration based on acousto-optic (AO) diffraction of two eigenmodes of a crystal on a single acoustic wave. It is shown that AO filters, based on the use of such diffraction, ensure the enhancement of the two-dimensional image edge during its optical Fourier processing. The main theoretical conclusions are experimentally confirmed using an AO paratellurite filter. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Multiple-beam fibre reflection interferometer based on an all-dielectric diffraction structure

We report experiments aimed at making a fibre reflection interferometer based on all-dielectric diffraction structures for the range 1500–1600 nm. The diffractive scattering structure of the input mirror of the interferometer is produced on the fibre end face by damaging it using abrasive diamond film with a grain size of a few microns. As a result, sharp reflection peaks are obtained for two interferometers, with the following parameters: finesse, 100 and 11; contrast, 2 and 60, respectively. Such an interferometer can, in principle, combine high contrast and high finesse. (laser applications and other topics in quantum electronics)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Two-dimensional image edge enhancement using two orders of Bragg diffraction

The process of two-dimensional image edge enhancement with an acousto-optical spatial filter using two orders of light diffraction is studied. It is theoretically shown that the diffraction that occurs in a paratellurite crystal on a ‘slow’ acoustic wave propagating orthogonally to the optical axis of the crystal allows enhancing a two-dimensional edge of an image, transferred by optical radiation with a wavelength of 0.63 μm in a wide band of acoustic frequencies 25 – 50 MHz. Enhancement of a two-dimensional image edge at an acoustic frequency of 29 MHz is experimentally demonstrated. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Imaging electron-density fluctuations by multidimensional X-ray photon-coincidence diffraction

The ultrafast spontaneous electron-density fluctuation dynamics in molecules is studied theoretically by off-resonant multiple X-ray diffraction events. The time- and wavevector-resolved photon-coincidence signals give an image of electron-density fluctuations expressed through the four-point correlation function of the charge density in momentum space. A Fourier transform of the signal provides a real-space image of the multipoint charge-density correlation functions, which reveal snapshots of the evolving electron density in between the diffraction events. The proposed technique is illustrated by ab initio simulations of the momentum- and real-space inelastic scattering signals from a linear cyanotetracetylene molecule.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

In situ X-ray diffraction of silicate liquids and glasses under dynamic and static compression to megabar pressures

Properties of liquid silicates under high-pressure and high-temperature conditions are critical for modeling the dynamics and solidification mechanisms of the magma ocean in the early Earth, as well as for constraining entrainment of melts in the mantle and in the present-day core–mantle boundary. In this paper, we present in situ structural measurements by X-ray diffraction of selected amorphous silicates compressed statically in diamond anvil cells (up to 157 GPa at room temperature) or dynamically by laser-generated shock compression (up to 130 GPa and 6,000 K along the MgSiO 3 glass Hugoniot). The X-ray diffraction patterns of silicate glasses and liquids reveal similar characteristics over a wide pressure and temperature range. Beyond the increase in Si coordination observed at 20 GPa, we find no evidence for major structural changes occurring in the silicate melts studied up to pressures and temperatures exceeding Earth’s core mantle boundary conditions. This result is supported by molecular dynamics calculations. Our findings reinforce the widely used assumption that the silicate glasses studies are appropriate structural analogs for understanding the atomic arrangement of silicate liquids at these high pressures.

58 GEOSCIENCES↗
DOE OSTI2021

Imaging conical intersection dynamics during azobenzene photoisomerization by ultrafast X-ray diffraction

Significance Vibronic coherences are unique features that emerge in the decisive moments of photochemistry and photophysics. Here we demonstrate how X-ray diffraction can access fundamental information about these coherences. This is enabled by recent developments at free-electron lasers, working toward temporal resolution and single-molecule accessibility of scattering-based measurements. Time-resolved diffraction patterns of the isomerization of azobenzene are simulated. The process is monitored in time via the momentum-space signal, with a special focus on the mixed elastic/inelastic scattering from coherences. We give practical ideas on how this relatively weak contribution to the signal can potentially be retrieved. A direct connection to the real-space movie of the conical intersection dynamics is made, enabling the observation of quantum coherences that direct chemical processes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Unveiling the spatial distribution of molecular coherences at conical intersections by covariance X-ray diffraction signals

Significance Monitoring the real-space motion of the electrons directly involved in ultrafast molecular dynamics is a challenging goal, hindered by the strong contributions of the remaining inactive electrons. Molecular quantum coherences can provide a direct window into elementary electronic dynamics, but they could not be separately imaged so far. Here, we demonstrate a time- and frequency-resolved X-ray diffraction technique, which can employ existing stochastic X-ray pulses to separately image the coherence contributions. The technique can selectively follow the relevant electrons involved in the ultrafast dynamics and identify the confined molecular regions covered by their motion. It enables readily feasible measurements and can be straightforwardly extended to full three-dimensional imaging via X-ray and electron diffraction.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2023

hpMCA: A Python-based Graphical Program for Energy Dispersive X-Ray Diffraction Data Collection and Analysis

Energy-dispersive X-ray diffraction (EDXD) at synchrotron beamlines is commonly used for the study of material properties under high pressure and/or high temperature. Experimenters typically rely on the availability of robust data collection and analysis at a beamline, but this has become increasingly difficult, especially with the introduction of multi-element detectors that generate complex, multi-dimensional data sets. These data sets have energy resolution, and they can also be resolved in relation to sample position, diffraction angle, or different external stimuli. We report a new Python-based graphical program, hpMCA, for EDXD data collection and analysis that streamlines the experimental process for the beamline users. The program features a user-friendly interface, capability for online viewing and analyzing data from multi-element energy-dispersive detectors, and includes features useful for working with samples under high pressure and/or high temperature, such as crystal phase identification, real-time unit cell lattice refinement, and pressure determination based on an equation of state.

data analysis software↗
DOE OSTI2018

In situ high-energy X-ray diffraction mapping of Lüders band propagation in medium-Mn transformation-induced plasticity steels

Two-dimensional distributions of microstructural characteristics of austenite (γ) around the Lüders band in medium-Mn transformation-induced plasticity (TRIP) steel were revealed by in situ high-energy X-ray diffraction. Lüders band propagation leads to significant changes in the volume fraction and lattice strains of austenite. The evolution of the lattice strain of γ-311 accords well with the true yield behavior model and is used to estimate the angle of the Lüders band front with respect to the tensile axis. The modified Williamson-Hall analysis shows that the dislocation density in austenite increased from 7 × 10 14 m -2 to 1.5 × 10 15 m -2 after Lüders band propagation. This in situ high-energy X-ray diffraction study unravels two-dimensional distribution of microstructural evolution during Lüders band propagation in medium-Mn TRIP steels.

36 MATERIALS SCIENCE↗
DOE OSTI2013

SIMULTANEOUS EXOPLANET CHARACTERIZATION AND DEEP WIDE-FIELD IMAGING WITH A DIFFRACTIVE PUPIL TELESCOPE

High-precision astrometry can identify exoplanets and measure their orbits and masses while coronagraphic imaging enables detailed characterization of their physical properties and atmospheric compositions through spectroscopy. In a previous paper, we showed that a diffractive pupil telescope (DPT) in space can enable sub-{mu}as accuracy astrometric measurements from wide-field images by creating faint but sharp diffraction spikes around the bright target star. The DPT allows simultaneous astrometric measurement and coronagraphic imaging, and we discuss and quantify in this paper the scientific benefits of this combination for exoplanet science investigations: identification of exoplanets with increased sensitivity and robustness, and ability to measure planetary masses to high accuracy. We show how using both measurements to identify planets and measure their masses offers greater sensitivity and provides more reliable measurements than possible with separate missions, and therefore results in a large gain in mission efficiency. The combined measurements reliably identify potentially habitable planets in multiple systems with a few observations, while astrometry or imaging alone would require many measurements over a long time baseline. In addition, the combined measurement allows direct determination of stellar masses to percent-level accuracy, using planets as test particles. We also show that the DPT maintains the full sensitivity of the telescope for deep wide-field imaging, and is therefore compatible with simultaneous scientific observations unrelated to exoplanets. We conclude that astrometry, coronagraphy, and deep wide-field imaging can be performed simultaneously on a single telescope without significant negative impact on the performance of any of the three techniques.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

Neutron diffraction and electrical transport studies on the incommensurate magnetic phase transition in holmium at high pressures

Neutron diffraction and electrical transport measurements have been made on the heavy rare earth metal holmium at high pressures and low temperatures in order to elucidate its transition from a paramagnetic (PM) to a helical antiferromagnetic (AFM) ordered phase as a function of pressure. The electrical resistance measurements show a change in the resistance slope as the temperature is lowered through the antiferromagnetic Neel temperature. The temperature of this antiferromagnetic transition decreases from approximately 122 K at ambient pressure at a rate of -4.9 K GPa(-1) up to a pressure of 9 GPa, whereupon the PM-to-AFM transition vanishes for higher pressures. Neutron diffraction measurements as a function of pressure at 89 and 110 K confirm the incommensurate nature of the phase transition associated with the antiferromagnetic ordering of the magnetic moments in a helical arrangement and that the ordering occurs at similar pressures as determined from the resistance results for these temperatures.

High Pressure↗
DOE OSTI2016

Anti-site mixing and magnetic properties of Fe 3 Co 3 Nb 2 studied via neutron powder diffraction

Here, we studied the crystal structure and magnetic properties of the rare-earth-free intermetallic compound Fe 3 Co 3 Nb 2 , which has recently been demonstrated to have potentially high magnetic anisotropy, using temperature-dependent neutron powder diffraction. Furthermore, the temperature dependence of the diffraction spectra reveals a magnetic transition between 300 and 400 K, in agreement with the magnetometry measurements. According to the structural refinement of the paramagnetic state and the substantial magnetic contribution to the diffuse scattering in the ferromagnetic state, the Fe/Co anti-site mixing is so strong that the site occupation for Fe and Co is almost random. The projection of the magnetic moments turned out to be non-zero along the c axis and in the a–b plane of Fe 3 Co 3 Nb 2 , most likely because of the exchange interactions between the randomly orientated nanograins in the samples. These findings suggest that future studies on the magnetism of Fe 3 Co 3 Nb 2 need to take the Fe/Co anti-site mixing into account, and the exchange interactions need to be suppressed to obtain large remanence and coercivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Magnetic phase diagram of (Mo 2/3 RE 1/3 ) 2 AlC, RE = Tb and Dy, studied by magnetization, specific heat, and neutron diffraction analysis

We report the results of magnetization, heat capacity, and neutron diffraction measurements on (Mo 2/3 RE 1/3 ) 2 AlC with RE = Dy and Tb. Temperature and field-dependent magnetization as well as heat capacity were measured on a powder sample and on a single crystal allowing the construction of the magnetic field-temperature phase diagram. To study the magnetic structure of each magnetic phase, we applied neutron diffraction in a magnetic field up to 6 T. For (Mo 2/3 Dy 1/3 ) 2 AlC in zero field, a spin density wave is stabilized at 16 K, with antiferromagnetic ordering at 13 K. Furthermore, we identify the coexistence of ferromagnetic and antiferromagnetic phases induced by magnetic fields for both RE = Tb and Dy. The origin of the field induced phases is resulting from the competing ferromagnetic and antiferromagnetic interactions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Grain size and structure distortion characterization of α-MgAgSb thermoelectric material by powder diffraction

Nanostructuring, structure distortion and/or disorder are the main manipulation techniques to reduce the lattice thermal conductivity and improve the figure of merit of thermoelectric materials. A single-phase α-MgAgSb sample, MgAg 0.97 Sb 0.99 , with high thermoelectric performance in near room temperature region was synthesized through a high-energy ball milling with a hot-pressing method. In this work, we report the average grain size of 24-28 nm and the accurate structure distortion, which are characterized by high-resolution neutron diffraction and synchrotron X-ray diffraction with Rietveld refinement data analysis. Both the small grain size and the structure distortion have a contribution to the low lattice thermal conductivity in MgAg 0.97 Sb 0.99 .

36 MATERIALS SCIENCE↗
DOE OSTI2011

IMAGING SPECTROSCOPY USING AIA DIFFRACTION PATTERNS IN CONJUNCTION WITH RHESSI AND EVE OBSERVATIONS

Extreme-ultraviolet (EUV) spectroscopy is a very powerful tool that can be used for probing the dynamic response of the solar corona and chromosphere during solar flares. Here we present a unique application of observations from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory using the artifacts of diffraction and dispersion. Using these techniques we can achieve imaging spectroscopy at the resolution of AIA (0.''6 plate scale) and at the revolutionary cadence of the instrument (nominally 12 s) for the brightest (saturated) pixels during solar flares. Analyzing the dispersion and diffraction effects that are observed as a result of the support grids used for the instrument's front filters, we can achieve up to 0.5 A spectral resolution across the EUV, optically thin passbands. Here we describe the technique used and present the first result of its application-the emission measure distribution for a single pixel at the top of a flaring loop. We analyze the AIA dispersion spectrum in conjunction with Extreme Ultraviolet Variability Experiment observations and spectroscopic and imaging results from the Reuven Ramaty High Energy Solar Spectroscopic Imager.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

DIFFRACTION, REFRACTION, AND REFLECTION OF AN EXTREME-ULTRAVIOLET WAVE OBSERVED DURING ITS INTERACTIONS WITH REMOTE ACTIVE REGIONS

We present observations of the diffraction, refraction, and reflection of a global extreme-ultraviolet (EUV) wave propagating in the solar corona. These intriguing phenomena are observed when the wave interacts with two remote active regions, and together they exhibit properties of an EUV wave. When the wave approached AR11465, it became weaker and finally disappeared in the active region, but a few minutes later a new wavefront appeared behind the active region, and it was not concentric with the incoming wave. In addition, a reflected wave was also simultaneously observed on the wave incoming side. When the wave approached AR11459, it transmitted through the active region directly and without reflection. The formation of the new wavefront and the transmission could be explained with diffraction and refraction effects, respectively. We propose that the different behaviors observed during the interactions may be caused by different speed gradients at the boundaries of the two active regions. We find that the EUV wave formed ahead of a group of expanding loops a few minutes after the start of the loops' expansion, which represents the initiation of the associated coronal mass ejection (CME). Based on these results, we conclude that the EUV wave should be a nonlinear magnetosonic wave or shock driven by the associated CME, which propagated faster than the ambient fast mode speed and gradually slowed down to an ordinary linear wave. Our observations support the hybrid model that includes both fast wave and slow non-wave components.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗