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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 1,009 records · Page 56
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

MHz free electron laser x-ray diffraction and modeling of pulsed laser heated diamond anvil cell

A new diamond anvil cell experimental approach has been implemented at the European x-ray Free Electron Laser, combining pulsed laser heating with MHz x-ray diffraction. In this report we use this setup to determine liquidus temperatures under extreme conditions, based on the determination of time-resolved crystallization. The focus is on a Fe-Si-O ternary system, relevant for planetary cores. This time-resolved diagnostic is complemented by a finite-element model, reproducing temporal temperature profiles measured experimentally using streaked optical pyrometry. This model calculates the temperature and strain fields by including (i) pressure and temperature dependencies of material properties, and (ii) the heat-induced thermal stress, including feedback effect on material parameter variations. Making our model more realistic, these improvements are critical as they give 7000 K temperature differences compared to previous models. Laser intensities are determined by seeking minimal deviation between measured and modeled temperatures. Combining models and streak optical pyrometry data extends temperature determination below detection limit. The presented approach can be used to infer the liquidus temperature by the appearance of SiO 2 diffraction spots. In addition, temperatures obtained by the model agree with crystallization temperatures reported for Fe–Si alloys. Our model reproduces the planetary relevant experimental conditions, providing temperature, pressure, and volume conditions. Those predictions are then used to determine liquidus temperatures at experimental timescales where chemical migration is limited. This synergy of novel time-resolved experiments and finite-element modeling pushes further the interpretation capabilities in diamond anvil cell experiments.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Time-resolved X-ray diffraction diagnostic development for the National Ignition Facility

Here we present the development of an experimental platform that can collect four frames of x-ray diffraction data along a single line of sight during laser-driven, dynamic-compression experiments at the National Ignition Facility. The platform is comprised of a diagnostic imager built around ultrafast sensors with a 2-ns integration time, a custom target assembly that serves also to shield the imager, and a 10-ns duration, quasi-monochromatic x-ray source produced by laser-generated plasma. We demonstrate the performance with diffraction data for Pb ramp compressed to 150 GPa and illuminated by a Ge x-ray source that produces ∼7 × 10 11 , 10.25-keV photons/ns at the 400 μm diameter sample.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Decoding diffraction and spectroscopy data with machine learning: A tutorial

This Tutorial provides a step-by-step guide on how to apply supervised machine-learning techniques to analyze diffraction and spectroscopy data. This Tutorial details four models—a reconstruction-focused model, a regression-focused model, a hybrid reconstruction/regression model, and a multimodal model—that use x-ray diffraction profiles and vibrational density of states spectra to predict various microstructural descriptors. In this Tutorial, we cover data pre-processing steps, constructions of the models via dimensionality reduction and regression, training, and analysis of these models. Comparisons of the model’s performance are provided, highlighting the strength and weakness of the various approaches utilized.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Fresnel diffraction imaging of surface nanostructure using coherent resonant x-ray scattering

We investigated surface nanostructures on an antiferromagnet MnBi 2 Te 4 using a novel imaging technique, direct (real)-space and real time coherent x-ray imaging (direct-CXI). This technique has provided new insights into antiferromagnetic textures, including the formation of anti-phase antiferromagnetic (AFM) domains and thermal dynamics of AFM domains and domain walls. While this method produces real-space images of AFM textures without requiring a complex imaging retrieval process, its underlying imaging mechanism has not been fully understood, limiting a deep understanding of AFM textures and the information they contain. By investigating the well-defined structural characteristics of the nanostructures fabricated on MnBi 2 Te 4 ⁠, we elucidate the imaging principle of this novel technique. We find that the observed images can be well explained by the Fresnel diffraction integral. Using a simple model from classical optics, our calculations successfully reproduce the experimentally observed images of the nanostructures. This demonstrates that direct-CXI not only provides straightforward real-space imaging but also contains phase information through its Fresnel diffraction integral.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Investigating the ultraviolet photodissociation of bromocyclopropane with ultrafast electron diffraction

We have studied the photodissociation of gas-phase bromocyclopropane by 200 nm wavelength ultraviolet radiation using ultrafast electron diffraction. Bromocyclopropane is a prototypical molecule in the study of organobromides, a class of molecules that have a significant impact on atmospheric ozone depletion through their photochemistry. Here, previous studies have revealed two possible reaction pathways for the photodissociation of bromine from bromocyclopropane; either the C–Br bond dissociates, leaving behind a cyclopropyl ring, or there is a concerted opening of the cyclopropyl ring along with the C–Br bond dissociation. In this work, both our experimental and simulation results indicate that the majority of the UV-photoexcited BCP molecules (88% ± 11% in the experiment) follow the first reaction pathway, in which the cyclopropyl ring remains closed after homolytic C–Br bond cleavage. This direct bond dissociation occurs within the experimental time resolution of 270 fs. In order to differentiate between the possible reaction end-products, both of which have diffraction signals dominated by the bromine atom, a new analysis method has been employed, which is more sensitive to the structure of the end-products.

Atmospheric chemistry↗
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 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↗