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At least 343 records · Page 19

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NASA NTRS1970

Elimination of coherent noise in a coherent light imaging system

Optical imaging systems using coherent light introduce objectionable noise into the output image plane. Dust and bubbles on and in lenses cause most of the noise in the output image. This noise usually appears as bull's-eye diffraction patterns in the image. By rotating the lens about the optical axis these diffraction patterns can be essentially eliminated. The technique does not destroy the spatial coherence of the light and permits spatial filtering of the input plane.

Grebowsky, G. J.↗

DOE OSTI2015

Imaging transient melting of a nanocrystal using an X-ray laser

Significance Despite phase transitions, such as melting, being ubiquitous in nature, understanding what occurs at the nanoscale (such as in nanocrystals) has so far remained challenging. With ensemble studies of nanocrystals it is often difficult to discriminate between intrinsic size-dependent properties and effects due to sample size and shape dispersity. Here, using an X-ray free electron laser we image the reversible melting of an individual nanocrystal induced by an ultrashort laser. It is revealed that the melting occurs transiently, repeatably, and inhomogeneously. This is consistent with a core-shell model where the exterior is melted and a solid core remains. These findings reveal, unambiguously, that core-shell melting occurs, which has important implications for understanding nanoscale phenomena.

Clark, Jesse N.↗

DOE OSTI2025

X-ray microscopy and talbot imaging with the matter in extreme conditions X-ray imager at LCLS

The last decade has shown the great potential that X-ray Free Electron Lasers (FEL) have to study High Energy Density (HED) physics. Experiments at FELs have made significant breakthroughs in Shock Physics and Dynamic Diffraction, Dense Plasma Physics and Warm Dense Matter Science, using techniques such as isochoric heating, inelastic scattering, small angle scattering and X-ray diffraction. In addition, and complementary to these techniques, the coherent properties of the FEL beam can be used to image HED samples with high fidelity. We present new imaging diagnostics and techniques developed at the Matter in Extreme Conditions (MEC) instrument at Linac Coherent Light Source (LCLS) over the last few years. We show results in Phase Contrast Imaging geometry, where the X-ray beam propagates from the target to a camera revealing its phase, as well as in Direct Imaging geometry, where a real image of the sample plane is produced in the camera with a spatial resolution down to 200 nm. Last, we show an implementation of the Talbot Imaging method allowing both X-ray phase and intensity measurements change introduced by a target with sub-micron resolution.

47 OTHER INSTRUMENTATION↗

DOE OSTI2023

Asymmetric nanoparticle oxidation observed in-situ by the evolution of diffraction contrast

Abstract The use of transmission electron microscopy (TEM) to observe real-time structural and compositional changes has proven to be a valuable tool for understanding the dynamic behavior of nanomaterials. However, identifying the nanoparticles of interest typically require an obvious change in position, size, or structure, as compositional changes may not be noticeable during the experiment. Oxidation or reduction can often result in subtle volume changes only, so elucidating mechanisms in real-time requires atomic-scale resolution or in-situ electron energy loss spectroscopy, which may not be widely accessible. Here, by monitoring the evolution of diffraction contrast, we can observe both structural and compositional changes in iron oxide nanoparticles, specifically the oxidation from a wüstite-magnetite (FeO@Fe 3 O 4 ) core – shell nanoparticle to single crystalline magnetite, Fe 3 O 4 nanoparticle. The in-situ TEM images reveal a distinctive light and dark contrast known as the ‘Ashby-Brown contrast’, which is a result of coherent strain across the core – shell interface. As the nanoparticles fully oxidize to Fe 3 O 4 , the diffraction contrast evolves and then disappears completely, which is then confirmed by modeling and simulation of TEM images. This represents a new, simplified approach to tracking the oxidation or reduction mechanisms of nanoparticles using in-situ TEM experiments.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Sub-pixel high-resolution imaging of high-energy x-rays inspired by sub-wavelength optical imaging

We have developed and demonstrated an image super-resolution method—XR-UNLOC: X-Ray UNsupervised particle LOCalization—for hard x-rays measured with fast-frame-rate detectors that is an adaptation of the principle of photo-activated localization microscopy (PALM) and stochastic optical reconstruction microscopy (STORM), which enabled biological fluorescence imaging at sub-optical-wavelength scales. We demonstrate the approach on experimental coherent Bragg diffraction data measured with 52 keV x-rays from a nanocrystalline sample. From this sample, we resolve the fine fringe detail of a high-energy x-ray Bragg coherent diffraction pattern to an upsampling factor of 16 of the native pixel pitch of 30 μ m of a charge-integrating fastCCD detector. This was accomplished by analysis of individual photon locations in a series of “nearly-dark” instances of the diffraction pattern that each contain only a handful of photons. Central to our approach was the adaptation of the UNLOC photon fitting routine for PALM/STORM to the hard x-ray regime to handle much smaller point spread functions, which required a different statistical test for photon detection and for sub-pixel localization. A comparison to a photon-localization strategy used in the x-ray community (“droplet analysis”) showed that XR-UNLOC provides significant improvement in super-resolution. We also developed a metric by which to estimate the limit of reliable upsampling with XR-UNLOC under a given set of experimental conditions in terms of the signal-to-noise ratio of a photon detection event and the size of the point spread function for guiding future x-ray experiments in many disciplines where detector pixelation limits must be overcome.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2022

Diffraction enhanced imaging utilizing a laser produced x-ray source

Image formation by Fresnel diffraction utilizes both absorption and phase-contrast to measure electron density profiles. The low spatial and spectral coherence requirements allow the technique to be performed with a laser-produced x-ray source coupled with a narrow slit. This makes it an excellent candidate for probing interfaces between materials at extreme conditions, which can only be generated at large-scale laser or pulsed power facilities. Here, we present the results from a proof-of-principle experiment demonstrating an effective ~2 μm laser-generated source at the OMEGA Laser Facility. This was achieved using slits of 1 × 30 μm 2 and 2 × 40 μm 2 geometry, which were milled into 30 μm thick Ta plates. Combining these slits with a vanadium He-like 5.2 keV source created a 1D imaging system capable of micrometer-scale resolution. The principal obstacles to achieving an effective 1 μm source are the slit tilt and taper—where the use of a tapered slit is necessary to increase the alignment tolerance. We demonstrate an effective source size by imaging a 2 ± 0.2 μm radius tungsten wire.

3D printing↗

DOE OSTI2024

Ultrastable cathodes enabled by compositional and structural dual-gradient design

Cathodes for next-generation batteries are pressed for higher voltage operation (≥4.5 V) to achieve high capacity with long cyclability and thermal tolerance. Current cathodes fail to meet these requirements owing to structural and electrochemical strains at high voltages, leading to fast capacity fading. Here, in this work, we present a cathode with a coherent architecture ranging from ordered to disordered frameworks with concentration gradient and controllable Ni oxidation activities, which can overcome voltage ceilings imposed by existing cathodes. This design enables simultaneous high-capacity and high-voltage operation at 4.5 V without capacity fading, and up to 4.7 V with negligible capacity decay. Multiscale diffraction and imaging techniques reveal the disordered surface is electrochemically and structurally indestructible, preventing surface parasitic reactions and phase transitions. Structural coherence from ordering to disordering limits lattice parameter changes, mitigating lattice strain and enhancing morphological integrity. The dual-gradient design also notably improves thermal stability, driving the advancement of high-performance cathode materials.

36 MATERIALS SCIENCE↗

NASA NTRS2012

Electric Field Reconstruction in the Image Plane of a High-Contrast Coronagraph Using a Set of Pinholes around the Lyot Plane

In a setup similar to the self coherent camera, we have added a set of pinholes in the diffraction ring of the Lyot plane in a high-contrast stellar Lyot coronagraph. We describe a novel complex electric field reconstruction from image plane intensity measurements consisting of light in the coronagraph's dark hole interfering with light from the pinholes. The image plane field is modified by letting light through one pinhole at a time. In addition to estimation of the field at the science camera, this method allows for self-calibration of the probes by letting light through the pinholes in various permutations while blocking the main Lyot opening. We present results of estimation and calibration from the High Contrast Imaging Testbed along with a comparison to the pair-wise deformable mirror diversity based estimation technique. Tests are carried out in narrow-band light and over a composite 10% bandpass.

coronagraphs↗

DOE OSTI2016

Bragg projection ptychography on niobium phase domain

Here, we demonstrate that the highly sensitive phase-contrast properties of Bragg coherent diffraction measurements combined with the translational diversity of ptychography can provide a Bragg “dark field” imaging method capable of revealing the finger print of domain structure in metallic thin films. Experimental diffraction data was taken from a epitaxially grown niobium metallic thin film on sapphire; and analyzed with the help of a careful combination of implemented refinement mechanisms.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Real-space observation of fluctuating antiferromagnetic domains

Magnetic domains play a fundamental role in physics of magnetism and its technological applications. Dynamics of antiferromagnetic domains is poorly understood, although antiferromagnets are expected to be extensively used in future electronic devices wherein it determines the stability and operational speed. Dynamics of antiferromagnets also features prominently in the studies of topological quantum matter. Real-space imaging of fluctuating antiferromagnetic domains is therefore highly desired but has never been demonstrated. We use coherent x-ray diffraction to obtain videos of fluctuating micrometer-scale antiferromagnetic domains in Ni 2 MnTeO 6 on time scales from 10 -1 to 10 3 s. In the collinear phase, thermally activated domain wall motion is observed in the vicinity of the Néel temperature. Unexpectedly, the fluctuations persist through the full range of the higher-temperature helical phase. These observations illustrate the high potential significance of the dynamic domain imaging in phase transition studies and in magnetic device research.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

NASA NTRS1971

Noise diffraction patterns eliminated in coherent optical systems

Lens rotation technique of noise diffraction pattern elimination spreads diffracted energy, normally concentrated over small area of image, over much larger annular area. Technique advantages include simplified lens selecting process, reduced clean room requirements, and low cost equipment requirements.

Grebowsky, G. R.↗

DOE OSTI2014

Parallel ptychographic reconstruction

Ptychography is an imaging method whereby a coherent beam is scanned across an object, and an image is obtained by iterative phasing of the set of diffraction patterns. It is able to be used to image extended objects at a resolution limited by scattering strength of the object and detector geometry, rather than at an optics-imposed limit. As technical advances allow larger fields to be imaged, computational challenges arise for reconstructing the correspondingly larger data volumes, yet at the same time there is also a need to deliver reconstructed images immediately so that one can evaluate the next steps to take in an experiment. Here we present a parallel method for real-time ptychographic phase retrieval. It uses a hybrid parallel strategy to divide the computation between multiple graphics processing units (GPUs) and then employs novel techniques to merge sub-datasets into a single complex phase and amplitude image. Results are shown on a simulated specimen and a real dataset from an X-ray experiment conducted at a synchrotron light source.

97 MATHEMATICS AND COMPUTING↗

NASA NTRS1993

Direct 75 milliarcsecond images from the Multiple Mirror Telescope with adaptive optics

We report results from an adaptive optics system designed to provide imaging at the diffraction limit of resolution in the near-infrared at the Multiple Mirror Telescope (MMT). For the present experiment, the aperture consisted of five of the six primary mirrors of the MMT, operating as a coherently phased array. The largest components of the atmospherically induced wave-front aberration are the fluctuations in mean phase between the segments. These errors were derived in real time from the Fourier transform of short-exposure stellar images at 2.2 microns and corrected at an image of the telescope pupil with piston motion from a segmented adaptive mirror. At a correction rate of 43 Hz, this level of adaptive control resulted in an integrated image with a clear diffraction-limited component of 0.075 arcsec FWHM. This stabilized component is present directly in the light arriving at the detector and is not the result of postprocessing. We discuss future improvements to our adaptive wave-front control and its application to astronomical observations.

Lloyd-Hart, M.↗

DOE OSTI2015

Transmission electron microscopy study of precipitates in an artificially aged Al–12.7Si–0.7Mg alloy

An investigation of Al–12.7Si–0.7Mg alloy aged at 160 °C, 180 °C and 200 °C for 3 h was carried out in order to identify the precipitating phases. Regular transmission and high resolution electron microscopy (TEM and HREM) were employed for this purpose. The studies were focused on the dark spots and needle-shaped precipitates lying in (001){sub Al} plane. Based on the HREM observations, dark spots and needle-shaped precipitates have different characteristics. The results revealed that the ellipsoidal and needle-shaped precipitates along <100> direction of the matrix coexist in the alloy by tilting experiments at given aging condition. The ellipsoidal dark spot precipitates viewing along [001]{sub Al} is not cross-sectional image of needle-shaped precipitates along <001>{sub Al}. Needle-shaped precipitate is coherent with the matrix. The diffraction pattern associated with the ellipsoidal precipitates is consistent with β″ reported in literature. - Highlights: • Wrought Al–Si–Mg alloy has been investigated to identify the precipitating phases. • The ellipsoidal and needle-shaped precipitates coexist in wrought Al–Si–Mg alloy. • The needle-shaped and ellipsoidal precipitates exhibit different characteristics.

36 MATERIALS SCIENCE↗

DOE OSTI2026

Nonlinear reversal of photoexcitation on the attosecond time scale improves ultrafast X-ray diffraction images

The complex refractive index of a material governs its light-matter interactions, with intense light fields enabling tailored nonlinear optical responses. In the X-ray regime, rapid photoionization limits the potential of nonlinear techniques by inducing irreversible electronic damage. Here we demonstrate that intense, sub-femtosecond X-ray pulses, shorter than typical Auger decay times, can partially reverse photoexcitation via stimulated emission near atomic resonances. By analyzing thousands of coherent diffraction patterns and ion spectra from neon nanoparticles exposed to sub-fs and 15-fs pulses, we observe enhanced X-ray diffraction alongside reduced energy absorption for sub-fs pulses. Theoretical modeling attributes this to dynamics akin to Rabi flopping that prolong the lifetime of resonant states and suppress electronic bleaching. These findings suggest that ultrashort, intense X-ray pulses enable active control of X-ray refractive index and damage pathways, opening avenues for improved high-resolution imaging and nonlinear spectroscopy in complex nanoscale systems.

Ulmer, Anatoli [Universität Hamburg (Germany)] (OR↗

DOE OSTI2018

Controllable diffraction pattern in semiconductor quantum well based on quantum coherence

In this paper, we study properties of diffraction of a weak probe field interacting with a symmetric semiconductor quantum well that is coherently manipulated by a standing wave. Based on the theory of quantum coherent and of light diffraction, we can obtain distribution of the diffraction spectra of the probe field. We consider the influences of Kerr nonlinear effect on the diffraction pattern, and studies show the distribution of diffraction pattern can be controlled through choosing appropriate physical parameters of system. Kerr nonlinear effect can enhance the brightness of central pattern and improve the transmission efficiency of the incident beam. A controllable diffraction pattern has potential applications in some areas, such as design of quantum diffractive optical elements, grating imaging system, precision measurement and so on.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2025

Laser-driven ultrafast transmission electron microscopy

Recent advances in lasers and electron optics technology have allowed transmission electron microscopes to achieve high spatial and temporal resolution, making them capable of tracking atoms, charges and spin motions down to the attosecond and nanometre scales. This Primer discusses the most common and practical experimental implementation of time-resolved transmission electron microscopy and the stroboscopic mode for evaluating ultrafast reversible dynamics. An in-depth discussion of photo-induced near-field electron microscopy, a technique unique to laser-assisted electron microscopy, is also provided, covering its prospective applications in the study of coherent phenomena in quantum materials. The experimental strategies and limitations in investigating the structural dynamics of materials and nanostructures by imaging, diffraction and spectroscopy are also described in detail, with a direct comparison with more conventional and established techniques. Here, we provide key information for new researchers who intend to use ultrafast transmission electron microscopy to address new challenges in specific materials science, condensed matter and nanophotonics.

Transmission electron microscopy↗

DOE OSTI2018

Simultaneous 8.2 keV phase-contrast imaging and 24.6 keV X-ray diffraction from shock-compressed matter at the LCLS

In this paper, we demonstrate simultaneous phase-contrast imaging (PCI) and X-ray diffraction from shock compressed matter at the Matter in Extreme Conditions endstation, at the Linac Coherent Light Source (LCLS). We utilize the chromaticity from compound refractive X-ray lenses to focus the 24.6 keV 3rd order undulator harmonic of the LCLS to a spot size of 5 μm on target to perform X-ray diffraction. Simultaneous PCI from the 8.2 keV fundamental X-ray beam is used to visualize and measure the transient properties of the shock wave over a 500 μm field of view. Furthermore, we demonstrate the ability to extend the reciprocal space measurements by 5 Å –1 , relative to the fundamental X-ray energy, by utilizing X-ray diffraction from the 3rd harmonic of the LCLS.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗