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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 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Rectangular Relief Diffraction Gratings for Coherent Lidar Beam Scanning

The application of specialized rectangular relief transmission gratings to coherent lidar beam scanning is presented. Two types of surface relief transmission grating approaches are studied with an eye toward potential insertion of a constant thickness, diffractive scanner where refractive wedges now exist. The first diffractive approach uses vertically oriented relief structure in the surface of an optical flat; illumination of the diffractive scanner is off-normal in nature. The second grating design case describes rectangular relief structure slanted at a prescribed angle with respect to the surface. In this case, illumination is normal to the diffractive scanner. In both cases, performance predictions for 2.0 micron, circularly polarized light at beam deflection angles of 30 or 45 degrees are presented.

Cole, H. J.↗
NASA NTRS1979

Laser Doppler anemometer diagnostics in unsteady flows

The application of the laser Doppler anemometer (LDA) to unsteady flows is discussed with respect to necessary features of the signal processor, properties of the optical system, and the character of the flow under investigation. The discussion of signal processors includes consideration of frequency trackers, counter-type processors, particle properties, data rates, and statistics. Secondly, diffraction limitations for an optical system are viewed with respect to spatial resolution. Finally, the total velocity field is decomposed into its subfields and the feasibility of, criteria for, and possible types of conditional sampling are defined. Several reported LDA experiments using conditional sampling are presented to demonstrate the different techniques that may be used.

Orloff, K. L.↗
DOE OSTI2019

Precision Plasmonics with Monomers and Dimers of Spherical Gold Nanoparticles: Nonequilibrium Dynamics at the Time and Space Limits

Monomers and dimers of spherical gold nanoparticles (NPs) exhibit highly uniform plasmonic properties at the single-particle level due to their high structural homogeneity (precision plasmonics). Recent investigations in precision plasmonics have largely focused on static properties using conventional techniques such as transmission electron microscopy and optical dark-field microscopy. Here in this Feature Article, we first highlight the application of femtosecond time-resolved electron diffraction for monitoring the nonequilibrium dynamics of spherical gold NPs after ultrafast optical excitation. The analysis of the transient diffraction patterns allows us to directly obtain quantitative information on the incoherent excitation of the lattice, that is, heating upon electron–lattice equilibration, as well as on the development of strain due to lattice expansion on picosecond time scales. The controlled assembly of two spherical gold NPs into a dimer with a few nanometers gap leads to unique optical properties. Specifically, extremely high electric fields (hot spot) in the gap are generated upon resonant optical excitation. Conventional optical microscopy cannot spatially resolve this unique hot spot due to the optical diffraction limit. We therefore employed nonlinear photoemission electron microscopy to visualize hot spots in single dimers of spherical gold NPs. A quantitative comparison of different single dimers confirms the homogeneity of the hot spots on the single-particle level. Finally, overall, these initial results are highly encouraging because they pave the way to investigate nonequilibrium dynamics in highly uniform plasmonic nanostructures at the time and space limits.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Quantum Efficiency Enhancement of Bialkali Photocathodes by an Atomically Thin Layer on Substrates

Quantum efficiency (QE) enhancement in accelerator technology relevant to antimonide photocathodes (K 2 CsSb) is achieved by interfacing them with atomically thin 2D crystal layers. The enhancement occurs in a reflection mode, when a 2D crystal is placed in between the photocathodes and optically reflective substrates. Specifically, the peak QE at 405 nm (3.1 eV) increases by a relative 10%, whereas the long wavelength response at 633 nm (2.0 eV) increases by a relative 36% on average and up to 80% at localized “hot spot” regions when photocathodes are deposited onto graphene–coated stainless steel. There is a similar effect for photocathodes deposited on hexagonal boron nitride monolayer coatings using nickel substrates. The enhancement does not occur when reflective substrates are replaced with optically transparent sapphire. Optical transmission, X–ray diffraction (XRD), and X–ray fluorescence (XRF) revealed that thickness, crystal orientation, quality, and elemental stoichiometry of photocathodes do not appreciably change due to 2D crystal coatings. Furthermore these results suggest that optical interactions are responsible for the QE enhancements when 2D crystal sublayers are present on reflective substrates, and provide a pathway toward a simple method of QE enhancement in semiconductor photocathodes by an atomically thin 2D crystal on substrates.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Two-dimensional single crystal diamond refractive x-ray lens

The next generation light sources such as diffraction-limited storage rings and high repetition rate x-ray free-electron lasers will generate x-ray beams with significantly increased brilliance. These future machines will require X-ray optical components that are capable of handling higher instantaneous and average power densities while tailoring the properties of the x-ray beams for a variety of scientific experiments. Single crystal diamond is one of the best bulk materials for this application, because it is radiation hard, has a suitable uniform index of refraction and the best available thermal properties. In this paper we report on fabrication and experimental testing of a two-dimensional (2D) single crystal diamond compound refractive X-ray lenses (CRL). These lenses were manufactured using femto-second laser cutting and tested at the Advanced Photon Source of Argonne National Laboratory.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Optically controllable magnetism in atomically thin semiconductors

We report evidence that ferromagnetic order in electrostatically doped, monolayer transition metal dichalcogenide (TMD) semiconductors can be stabilized and controlled at zero magnetic field by local optical pumping. We use circular dichroism (CD) in reflectivity from excitonic states as a spatially resolved probe of charge-carrier spin polarization. At electron densities $n_e$ ~ 10 12 cm -2 , a diffraction-limited, circularly polarized optical pump breaks symmetry between oppositely polarized magnetic states and stabilizes long-range magnetic order, with carrier polarization exceeding 80% over an 8 μm by 5 μm extent. In time-resolved measurements with pulsed optical excitation, we observe that magnetic interactions amplify the initial pump-induced spin polarization by more than an order of magnitude. The optical control of magnetism with local optical pumps will unlock advancements in spin and optical technologies and provides a versatile tool in the study of correlated phases in two-dimensional electron gases.

36 MATERIALS SCIENCE↗
DOE OSTI2014

A scanning, all-fiber Sagnac interferometer for high resolution magneto-optic measurements at 820 nm

The Sagnac Interferometer has historically been used for detecting non-reciprocal phenomena, such as rotation. We demonstrate an apparatus in which this technique is employed for high resolution measurements of the Magneto-Optical Polar Kerr effect—a direct indicator of magnetism. Previous designs have incorporated free-space components which are bulky and difficult to align. We improve upon this technique by using all fiber-optic coupled components and demonstrate operation at a new wavelength, 820 nm, with which we can achieve better than 1 μrad resolution. Mounting the system on a piezo-electric scanner allows us to acquire diffraction limited images with 1.5 μm spatial resolution. We also provide extensive discussion on the details and of the Sagnac Interferometer's construction.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2022

Etched Silicon Planar CRL Optics for the High-Energy X-ray Diffraction Beamlines 11-ID-B and 11-ID-C at the APS

We report the focusing of high-energy X-rays is most commonly achieved by commercially available compound refractive lenses (CRL), which are added together in larger structures. There is a need for high-energy X-ray beamlines to enable focusing in only one dimension down to a few micrometers to study layered materials and thin films. High-energy X-rays above 50 keV require often 100 lenses or more, therefore it is more efficient to etch the complete arrays of lenses into a monolithic substrate like a silicon wafer. Custom lens arrays were fabricated for the high-energy x-ray beamlines 11-ID-B, and 11-ID-C at the Argonne National Laboratory. The fabrication required tuning parameters of the Bosch process to optimize the etching of deep vertical sidewalls at a reasonable speed without overheating. The beamline 11-ID-B is equipped with lens arrays of 85-110 lenses for 59 keV and 190-250 lenses for 87 keV photon energy, focusing the beam vertically below 5.0 µm at the sample positions between 1600 mm to 2100 mm. 11-ID-C has received arrays of 435 lenses that focus 106 keV X-rays to a vertical height of 2.0 µm at the sample position. In both cases, the flux density gain in the focal spot is larger than a factor of 20, relative to using slits to cut the beam size. The lens setup is permanently installed and can be moved in and out of the beam during the experiment without further alignment. The lenses have enabled operando diffraction studies on interfaces in batteries and the development of pair distribution function (PDF) analysis using grazing incidence geometry.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1974

Optical grating evaluator - A device for detailed measurement of diffraction grating efficiencies in the vacuum ultraviolet

A device for detailed measurement of diffraction grating efficiencies and over-all performance in the VUV has been designed and constructed at the Naval Research Laboratory. The system employs semiautomated mechanisms to scan the face of the grating with a narrow monochromatic beam, and an efficiency map of the grating surface is produced on a strip chart recorder. Grating efficiency in the various diffracted orders and intensity of light scattered between orders may also be measured. A unique feature is the ability to determine the angle and effectiveness of grating blaze and variations in blaze under different conditions of illumination.

Michels, D. J.↗
DOE OSTI2014

X-ray diagnostic developments in the perspective of DEMO

Soft X-ray diagnostics at present are not adequate for a burning plasma experiment, neither in term of hardware nor as diagnostic conception. Detectors have to be radiation tolerant, easily shielded, with low sensitivity to neutrons and gammas and with energy discrimination. Layout and viewing capability should be more flexible, thanks to the use also of optical devices, going toward a configuration intermediate between discrete tomography and pure imaging. The general conception of these diagnostics should therefore evolve in the direction of pattern recognition for a real time feedback. This work is focused on the diagnostic developments undertaken at the ENEA- Frascati X-ray Laboratory, following in particular three directions: gas detector for fast and advanced high density tomography, C-MOS solid state imaging detectors for slow control and X-ray polycapillary optics. GEM gas detectors in photon counting mode (noise free) were developed in the range 1-30 keV having high efficiency, high time resolution (up to microseconds), energy discrimination in bands and optical flexibility. Discrimination of X-rays, neutrons and gammas has been demonstrated, thanks to the combination of intrinsic gain and discrimination thresholds, at neutron fluxes (10{sup 7} n/s*cm{sup 2}) comparable with the expected ones at the ports of ITER. GEM detectors are also extremely flexible in the design, allowing optimization of the measurements and solutions for shielding or minimization of the effect of background radiation. Two solid state C-MOS imagers working in photon counting mode, one based on Si semiconductor (Medipix-2, range 5-30 keV) and the other one having a CdTe sensor (Pixirad, range 2-100 keV) have been characterized in laboratory. C-MOS imagers have features and performances thoroughly complementary to the GEM detector and, thanks to their higher pixel density, could be used as remote imaging detectors coupled to optics. X-ray polycapillary lenses have been therefore studied in the laboratory both as imaging optical device (full lens) or to define a line of sight (cylinder lens); the preliminary results are encouraging toward the goal of using these lenses to transport X-ray radiation far from the reactor. Reflective or diffractive X-ray optics can be also an option for tomography. A GEM detector has been installed at KSTAR and in the next future hopefully the other approaches will be tested there: once their feasibility will be demonstrated, the issue of the improvement of the radiation tolerance will be faced and the development of algorithms for data analysis as well.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS2006

Wave-Optics Analysis of Pupil Imaging

Pupil imaging performance is analyzed from the perspective of physical optics. A multi-plane diffraction model is constructed by propagating the scalar electromagnetic field, surface by surface, along the optical path comprising the pupil imaging optical system. Modeling results are compared with pupil images collected in the laboratory. The experimental setup, although generic for pupil imaging systems in general, has application to the James Webb Space Telescope (JWST) optical system characterization where the pupil images are used as a constraint to the wavefront sensing and control process. Practical design considerations follow from the diffraction modeling which are discussed in the context of the JWST Observatory.

Dean, Bruce H.↗
DOE OSTI2025

Optical Interference for the Guidance of Cryogenic Focused Ion Beam Milling Beyond the Axial Diffraction Limit

Using a tri-coincident cryogenic FIB-SEM-LM system, we identify an interferometric optical response that can be used for targeting lamella production to fluorescently labelled structures with accuracy beyond the diffraction limit. We demonstrate the approach using synthetic samples of fluorescent beads embedded in micron-scale droplets of water. Here, we then apply the approach to capture virions inside host cells. Successful targeting is confirmed by cryogenic electron tomography revealing clusters of virions in intracellular vesicles.

Sica, Anthony V. [SLAC National Accelerator Labora↗
DOE OSTI2020

In situ temperature profile measurements with high-energy X-rays as a probe of optical floating zone crystal growth environment

The ability of optical floating zone (OFZ) furnaces to rapidly produce large single crystals of complex emerging materials has had a transformative effect on many scientific fields that require samples of this type. However, the crystal growth process within the OFZ furnace is not well understood owing to the challenges involved in monitoring the high-temperature crystal growth process. Novel beamline-compatible optical furnaces that approximate the inhomogeneous growth environment within an OFZ furnace have been fabricated and tested in high-energy synchrotron beamlines. In this paper, it is demonstrated that temperature profiles can be effectively extracted from powder diffraction data collected on polycrystalline ceramic rods heated at their tip. Furthermore, these measured temperature profiles can be accurately reproduced using a heat-transfer model that accounts for solid-state thermal conduction, partial sample lamp power absorption, convective air cooling and radiative cooling, allowing key thermal parameters such as thermal conductivity to be extracted from experimental data.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Tip-enhanced near-field optical microscope with side-on and ATR-mode sample excitation for super-resolution Raman imaging of surfaces

A tip-enhanced near-field optical microscope with side-on and attenuated total reflectance (ATR) excitation and collection is described and used to demonstrate sub-diffraction-limited (super-resolution) optical and chemical characterization of surfaces. ATR illumination is combined with an Au optical antenna tip to show that (i) the tip can quantitatively transduce the optical near-field (evanescent waves) above the surface by scattering photons into the far-field, (ii) the ATR geometry enables excitation and characterization of surface plasmon polaritons (SPPs), whose associated optical fields are shown to enhance Raman scattering from a thin layer of copper phthalocyanine (CuPc), and (iii) SPPs can be used to plasmonically excite the tip for super-resolution chemical imaging of patterned CuPc via tip-enhanced Raman spectroscopy (TERS). ATR-illumination TERS is also quantitatively compared with the more conventional side-on illumination scheme. In both cases, spatial resolution was better than 40 nm and tip on/tip off Raman enhancement factors were >6500. Furthermore, ATR illumination was shown to provide similar Raman signal levels at lower “effective” pump powers due to additional optical energy delivered by SPPs to the active region in the tip-surface gap.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Noncollinear Acousto-Optic Filtering of Polychromatic Bessel Light Beams in Uniaxial Crystals

We have studied the features of noncollinear acousto-optic filtering of quasi-nondiffracting Bessel light beams in uniaxial crystals. We have obtained coupled wave equations for the vector amplitudes of an incident ordinary (o-type) Bessel beam and an extraordinary (e-type) diffracted beam for different modes. We have found an expression for the diffraction efficiency as a function of the parameters of interacting ordinary and extraordinary Bessel beams, and also as a function of the values of the overlap integrals. Using the overlap integral method, we have shown that regardless of the mode order for the Bessel light beam, under transverse phase matching conditions for ordinary and extraordinary diffracted Bessel beams in the optical spectral range 0.4–1.1 μm we can achieve a filter transmission bandwidth of ~0.6 nm in paratellurite crystals .

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Synthesis and crystal structure characterization of InGaZnO{sub 4} with a new defect structure

Single crystals of InGaZnO{sub 4} were synthesized in a sealed Pt-tube at elevated temperatures under normal pressure without flux. InGaZnO{sub 4} has a trigonal crystal system (R3{sup ¯}m; No. 166) deduced from convergent beam electron diffraction (CBED). Single crystal structure refinement from XRD data at −150 °C (a=3.275(1) Å; c=25.99(1) Å; Z=3) revealed an alternate stacking of InO{sub 6/3}{sup −} and (Ga,Zn)O{sub 4/4}{sup +} layers, iso-structural to YbFe{sub 2}O{sub 4}. The cell parameters at room temperature were refined from powder X-ray diffraction data (a=3.284(3) Å and c=26.037(3) Å). The transparent crystals have a gray-bluish color and exhibit an excess of Ga expressed by the cation ratio of In:Ga:Zn=30.2(9):39(1):31(1) determined by energy dispersive X-ray spectroscopy (EDXS). While the isovalent substitution of In{sup 3+} by Ga{sup 3+} is known, an additional aliovalent substitution of Zn{sup 2+} by Ga{sup 3+} is observed. This results in the formula (In{sub 0.9}Ga{sub 0.1})Ga{sub 1.06}Zn{sub 0.91}□{sub 0.03}O{sub 4} where 3% of the cations in 4+1 coordination are vacant due to aliovalent substitution. Further evidence of that defect structure is found in the lattice parameter a which is substantially smaller than in stoichiometric InGaZnO{sub 4}, as well as in the strong absorption in the near-IR from transitions correlated with the defect structure. The bluish color of the crystals is due to an enhanced absorption in the red of the visible spectrum. For the first time, we achieved to image InGaZnO{sub 4} at atomic resolution in the electron microscope proving a perfect periodic stacking of atomic layers. - Graphical abstract: Single crystals of InGaZnO{sub 4} have been synthesized at ambient pressure and analyzed with X-ray diffraction, electron microscopy, and optical absorption. Optical band gap and optical transmission have been determined. - Highlights: • Preparation of single crystals of InGaO{sub 3}(ZnO){sub 1} at ambient pressure for the first time. • Non-stoichiometric compound (In{sub 0.9}Ga{sub 0.1})Ga{sub 1.06}Zn{sub 0.91}□{sub 0.03}O{sub 4} with defect structure, excess of Ga, depletion of Zn. • Real structure of InGaO{sub 3}(ZnO){sub 1} imaged by high resolution TEM for the first time. • Optical band gap and transmission of InGaO{sub 3}(ZnO){sub 1} single crystal.

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

High energy electron diffraction instrument with tunable camera length

Ultrafast electron diffraction (UED) stands as a powerful technique for real-time observation of structural dynamics at the atomic level. In recent years, the use of MeV electrons from radio frequency guns has been widely adopted to take advantage of the relativistic suppression of the space charge effects that otherwise limit the temporal resolution of the technique. Nevertheless, there is not a clear choice for the optimal energy for a UED instrument. Scaling to beam energies higher than a few MeV does pose significant technical challenges, mainly related to the inherent increase in diffraction camera length associated with the smaller Bragg angles. In this study, we report a solution by using a compact post-sample magnetic optical system to magnify the diffraction pattern from a crystal Au sample illuminated by an 8.2 MeV electron beam. Our method employs, as one of the lenses of the optical system, a triplet of compact, high field gradients (>500 T/m), small-gap (3.5 mm) Halbach permanent magnet quadrupoles. Shifting the relative position of the quadrupoles, we demonstrate tuning the magnification by more than a factor of two, a 6× improvement in camera length, and reciprocal space resolution better than 0.1 Å –1 in agreement with beam transport simulations.

47 OTHER INSTRUMENTATION↗