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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 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Resonance-enhanced optical nonlinearity in the Weyl semimetal TaAs

The second-order conductivity of a material, σ (2) , relating current to the square of electric field, is nonzero only when inversion symmetry is broken, unlike the conventional linear conductivity. Second-order nonlinear optical responses are thus powerful tools in basic research as probes of symmetry breaking; they are also central to optical technology as the basis for generating photocurrents and frequency doubling. The recent surge of interest in Weyl semimetals with acentric crystal structures has led to the discovery of a host of σ (2) -related phenomena in this class of materials, such as polarization-selective conversion of light to dc current (photogalvanic effects) and the observation of giant second-harmonic generation (SHG) efficiency in TaAs at photon energy 1.5 eV. Here, we present measurements of the SHG spectrum of TaAs, revealing that the response at 1.5 eV corresponds to the high-energy tail of a resonance at 0.7 eV, at which point the second harmonic conductivity is approximately 200 times larger than seen in the standard candle nonlinear crystal, GaAs. This remarkably large SHG response provokes the question of ultimate limits on σ (2) , which we address by a new theorem relating frequency-integrated nonlinear response functions to the third cumulant (or "skewness") of the polarization distribution function in the ground state.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

A novel mitochondria-targeted two-photon fluorescent probe for dynamic and reversible detection of the redox cycles between peroxynitrite and glutathione

Highlights: • We report a two-photon fluorescent probe (TP-Se) for optical imaging. • TP-Se can monitor reversibly changes in ONOO{sup −}/GSH levels in mitochondria. • TP-Se will lead to significant development on redox events in cellular redox regulation. Redox homeostasis is important for maintenance of normal physiological functions within cells. Redox state of cells is primarily a consequence of precise balance between levels of reducing equivalents and reactive oxygen species. Redox homeostasis between peroxynitrite (ONOO{sup −}) and glutathione (GSH) is closely associated with physiological and pathological processes, such as prolonged relaxation in vascular tissues and smooth muscle preparations, attenuation of hepatic necrosis, and activation of matrix metalloproteinase-2. We report a two-photon fluorescent probe (TP-Se) based on water-soluble carbazole-based compound, which integrates with organic selenium, to monitor changes in ONOO{sup −}/GSH levels in cells. This probe can reversibly respond to ONOO{sup −} and GSH and exhibits high selectivity, sensitivity, and mitochondrial targeting. The probe was successfully applied to visualize changes in redox cycles during ONOO{sup −} outbreak and antioxidant GSH repair in cells. The probe will lead to significant development on redox events involved in cellular redox regulation.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Measuring excited state lifetime of Rb atoms with pump-probe technique

A technique for measuring the excited state lifetime τ{sub ex} of optical transitions in alkali atoms is presented. It is a form of pump-probe technique based on time-resolved optical transmission through the atomic vapor cell. This technique can serve as an alternative to the traditionally used time-resolved photofluorescence methods when measuring alkali vapor cells with heavily quenched fluorescence, where the τ{sub ex} is expected to be on the order of a few nanoseconds, and the highly sensitive fluorescence detectors with sub-nanosecond temporal resolution that are required may not be available. We use this technique to measure the τ{sub ex} of Rb atoms in vapor cells with different buffer gas pressures.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Spatially confined low-power optically pumped ultrafast synchrotron x-ray nanodiffraction

The combination of ultrafast optical excitation and time-resolved synchrotron x-ray nanodiffraction provides unique insight into the photoinduced dynamics of materials, with the spatial resolution required to probe individual nanostructures or small volumes within heterogeneous materials. Optically excited x-ray nanobeam experiments are challenging because the high total optical power required for experimentally relevant optical fluences leads to mechanical instability due to heating. For a given fluence, tightly focusing the optical excitation reduces the average optical power by more than three orders of magnitude and thus ensures sufficient thermal stability for x-ray nanobeam studies. Delivering optical pulses via a scannable fiber-coupled optical objective provides a well-defined excitation geometry during rotation and translation of the sample and allows the selective excitation of isolated areas within the sample. Finally, experimental studies of the photoinduced lattice dynamics of a 35 nm BiFeO 3 thin film on a SrTiO 3 substrate demonstrate the potential to excite and probe nanoscale volumes.

36 MATERIALS SCIENCE↗
NASA NTRS2006

Near Sun Free-Space Optical Communications from Space

Free-space optical communications offers expanded data return capacity, from probes distributed throughout the solar system and beyond. Space-borne and Earth-based optical transceivers used for communicating optically, will periodically encounter near Sun pointing. This will result in an increase in the scattered background light flux, often contributing to degraded link performance. The varying duration of near Sun pointing link operations relative to the location of space-probes, is discussed in this paper. The impact of near Sun pointing on link performance for a direct detection photon-counting communications system is analyzed for both ground- and space-based Earth receivers. Finally, impact of near Sun pointing on spaceborne optical transceivers is discussed.

free-space↗
DOE OSTI2026

Polarons are probes of the dynamic nanoscale environments found in electrochemically doped π-conjugated polymers

Charge carriers (i.e., polarons) in electrochemically doped organic (semi)conductors are proposed to be regulated by several physicochemical features, including the chemical compositions and structures of the π-conjugated frameworks of the semiconductor building blocks, the chemistry of the electrolyte (considering both the salt and solvent), multiscale and time-dependent morphology variations across the material as a function of electrochemical processes, and assorted permutations of these and other factors. To address these hypotheses, we investigate the energetic, optoelectronic, chemical, and local structural properties of negative polarons (radical anions) as a function of electrochemical doping in the donor–acceptor, π-conjugated redox copolymer P(NDI2OD-T2), also referred to as N2200. A critical finding is that there is not just “one type” of polaron in electrochemically doped P(NDI2OD-T2). Rather, an ensemble of polarons exists, with the polarons having optoelectronic signatures that are defined by their nanoscale environments. Importantly, the polaron optical signatures serve as local probes for how the operando electrochemical environments are dynamically working in concert to facilitate charge transport. Collectively, the distinctive and extensive integration of theory and measurement science presented here establishes a baseline for the roles that semiconductor and electrolyte chemistries and dynamic structural features have on polarons in electrochemically doped organic semiconductors and how these factors influence the energetics and rates of polaron transport.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Time-domain Brillouin scattering theory for probe light and acoustic beams propagating at an angle and acousto-optic interaction at material interfaces

A theory has been developed to interpret time-domain Brillouin scattering (TDBS) experiments involving coherent acoustic pulse (CAP) and light pulse beams propagating at an angle to each other. It predicts the influence of the directivity pattern of their acousto-optic interaction on TDBS signals when heterodyne detection of acoustically scattered light is in backward direction to incident light. The theory reveals relationships between the carrier frequency, amplitude and duration of acoustically induced ”wave packets” in light transient reflectivity signals, and factors such as CAP duration, widths of light and sound beams, and their interaction angle. It describes the transient dynamics of these wave packets when the light and CAP encounter material interfaces, and how the light scattering by the incident CAP transforms into scattering by the reflected and transmitted CAPs. The theory suggests that single-point TDBS experiments can determine not only depth positions of buried interfaces but also their local inclinations/orientations.

42 ENGINEERING↗
NASA NTRS2016

Titan-Like Exoplanets: Variations in Geometric Albedo and Effective Transit Height with Haze Production Rate

Extensive studies characterizing Titan present an opportunity to study the atmospheric properties of Titan-like exoplanets. Using an existing model of Titan's atmospheric haze, we computed geometric albedo spectra and effective transit height spectra for six values of the haze production rate (zero haze to twice present) over a wide range of wavelengths (0.2-2 microns). In the geometric albedo spectra, the slope in the UV-visible changes from blue to red when varying the haze production rate values from zero to twice the current Titan value. This spectral feature is the most effective way to characterize the haze production rates. Methane absorption bands in the visible-NIR compete with the absorbing haze, being more prominent for smaller haze production rates. The effective transit heights probe a region of the atmosphere where the haze and gas are optically thin and that is thus not effectively probed by the geometric albedo. The effective transit height decreases smoothly with increasing wavelength, from 376 km to 123 km at 0.2 and 2 microns, respectively. When decreasing the haze production rate, the methane absorption bands become more prominent, and the effective transit height decreases with a steeper slope with increasing wavelength. The slope of the geometric albedo in the UV-visible increases smoothly with increasing haze production rate, while the slope of the effective transit height spectra is not sensitive to the haze production rate other than showing a sharp rise when the haze production rate increases from zero. We conclude that geometric albedo spectra provide the most sensitive indicator of the haze production rate and the background Rayleigh gas. Our results suggest that important and complementary information can be obtained from the geometric albedo and motivates improvements in the technology for direct imaging of nearby exoplanets.

Geometric albedo↗
NASA NTRS2011

The SEDs and Host Galaxies of the Dustiest GRB Afterglows

The afterglows and host galaxies of long gamma-ray bursts (GRBs) offer unique opportunities to study star-forming galaxies in the high-z Universe, Until recently, however. the information inferred from GRB follow-up observations was mostly limited to optically bright afterglows. biasing all demographic studies against sight-lines that contain large amounts of dust. Aims. Here we present afterglow and host observations for a sample of bursts that are exemplary of previously missed ones because of high visual extinction (A(sub v) (Sup GRB) approx > 1 mag) along the sight-line. This facilitates an investigation of the properties, geometry and location of the absorbing dust of these poorly-explored host galaxies. and a comparison to hosts from optically-selected samples. Methods. This work is based on GROND optical/NIR and Swift/XRT X-ray observations of the afterglows, and multi-color imaging for eight GRB hosts. The afterglow and galaxy spectral energy distributions yield detailed insight into physical properties such as the dust and metal content along the GRB sight-line as well as galaxy-integrated characteristics like the host's stellar mass, luminosity. color-excess and star-formation rate. Results. For the eight afterglows considered in this study we report for the first time the redshift of GRBs 081109 (z = 0.97S7 +/- 0.0005). and the visual extinction towards GRBs 0801109 (A(sub v) (Sup GRB) = 3.4(sup +0.4) (sub -0.3) mag) and l00621A (A(sub v) (Sup GRB) = 3.8 +/- 0.2 mag), which are among the largest ever derived for GRB afterglows. Combined with non-extinguished GRBs. there is a strong anti-correlation between the afterglow's metals-to-dust ratio and visual extinction. The hosts of the dustiest afterglows are diverse in their properties, but on average redder(((R - K)(sub AB)) approximates 1.6 mag), more luminous ( approximates 0.9 L (sup *)) and massive ((log M(sup *) [M(solar]) approximates 9.8) than the hosts of optically-bright events. We hence probe a different galaxy population. suggesting that previous host samples miss most of the massive. chemically-evolved and metal-rich members. This also indicates that the dust along the sight-line is often related to host properties, and thus probably located in the diffuse ISM or interstellar clouds and not in the immediate GRB environment. Some of the hosts in our sample. are blue, young or of small stellar mass illustrating that even apparently non-extinguished galaxies possess very dusty sight-lines due to a patchy dust distribution. Conclusions. The afterglows and host galaxies of the dustiest GRBs provide evidence for a complex dust geometry in star-forming galaxies. In addition, they establish a population of luminous. massive and correspondingly chemically-evolved GRB hosts. This suggests that GRBs trace the global star-formation rate better than studies based on optically-selected host samples indicate, and the previously-claimed deficiency of high-mass host galaxies was at least partially a selection effect.

Kruhler, T.↗
DOE OSTI2020

The design of a line velocity interferometer for any reflector for inertial confinement experiments on the Z-machine

A line VISAR (Velocity Interferometer System for Any Reflector) has been designed and commissioned at the Sandia National Laboratory’s Z-machine. The instrument consists of an F/2 collection system, beam transport, and an interferometer table that contains two Mach–Zehnder type interferometers and an eight channel Gated Optical Imaging (GOI) system. The VISAR probe laser operates at the 532 nm wavelength, and the GOI bandpass is 540–600 nm. The output of each interferometer is passed to an optical streak camera with four selectable sweep speeds. The system is designed with three interchangeable optics modules to select a full field of view of 1 mm, 2 mm, or 4 mm. The optical beam transport system connects the target image plane to the interferometers and the gated optical imagers. The target is integrated into a sacrificial final optics assembly that is integral to the transport beamline.

Datte, P.↗
DOE OSTI2015

Fabrication of anti-adhesion surfaces on aluminium substrates of rubber plastic moulds using electrolysis plasma treatment

An anti-adhesion surface with a water contact angle of 167° was fabricated on aluminium samples of rubber plastic moulds by electrolysis plasma treatment using mixed electrolytes of C{sub 6}H{sub 5}O{sub 7}(NH{sub 4}){sub 3} and Na{sub 2}SO{sub 4}, followed by fluorination. To optimise the fabrication conditions, several important processing parameters such as the discharge voltage, discharge time, concentrations of supporting electrolyte and stearic acid ethanol solution were examined systematically. Using scanning electron microscopy (SEM) to analyse surfaces morphology, micrometer scale pits, and protrusions were found on the surface, with numerous nanometer mastoids contained in the protrusions. These binary micro/nano-scale structures, which are similar to the micro-structures of soil-burrowing animals, play a critical role in achieving low adhesion properties. Otherwise, the anti-adhesion behaviours of the resulting samples were analysed by the atomic force microscope (AFM), Fourier-transform infrared spectrophotometer (FTIR), electrons probe micro-analyzer (EPMA), optical contact angle meter, digital Vickers microhardness (Hv) tester, and electronic universal testing. The results show that the electrolysis plasma treatment does not require complex processing parameters, using a simple device, and is an environment-friendly and effective method. Under the optimised conditions, the contact angle (CA) for the modified anti-adhesion surface is up to 167°, the sliding angle (SA) is less than 2°, roughness of the sample surface is only 0.409μm. Moreover, the adhesion force and H{sub v} are 0. 9KN and 385, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Diagrammatic approach to nonlinear optical response with application to Weyl semimetals

Nonlinear optical responses are a crucial probe of physical systems including periodic solids. In the absence of electron-electron interactions, they are calculable with standard perturbation theory starting from the band structure of Bloch electrons, but the resulting formulas are often large and unwieldy, involving many energy denominators from intermediate states. This work gives a Feynman diagram approach to calculating nonlinear responses. This diagrammatic method is a systematic way to perform perturbation theory, which often offers shorter derivations and also provides a natural interpretation of nonlinear responses in terms of physical processes. Applying this method to second-order responses concisely reproduces formulas for the second-order-harmonic shift current. We then apply this method to third-order responses and derive formulas for third-order-harmonic generation and self-focusing of light, which can be directly applied to tight-binding models. Third-order responses in the semiclasscial regime include a Berry curvature quadrupole term, whose importance is discussed including symmetry considerations and when the Berry curvature quadrupole becomes the leading contribution. In conclusion, the method is applied to compute third-order optical responses for a model Weyl semimetal, where we find a new topological contribution that diverges in a clean material, as well as resonances with a peculiar linear character.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1982

Transonic applications of the Wake Imaging System

The extension of a rapid flow field survey method (wake imaging system) originally developed for low speed wind tunnel operation, to transonic wind tunnel applications is discussed. The advantage of the system, beside the simplicity and low cost of the data acquisition system, is that the probe position data are recorded as an optical image of the actual sensor and thus are unaffected by the inevitable deflections of the probe support. This permits traversing systems which are deliberately flexible and have unusual motions. Two transverse drive systems are described and several typical data images are given.

Crowder, J. P.↗
DOE OSTI2023

Optical design and synthetic analysis of the electron cyclotron emission imaging diagnostic of HL-2M tokamak

The electron cyclotron emission imaging (ECEI) diagnostic is a powerful tool to study the MHD and turbulent transport in magnetically confined fusion plasmas. In this work, the optical system including the local oscillator (LO) coupling and radio frequency (RF) receiving optics, has been designed and analyzed for the HL-2M ECEI diagnostic. The LO optics can illuminate the antenna array and drive the mixer diode to work efficiently, with more than 36% of the beam intensity for the channels which probe the plasma edge relative to those of channels which probe the plasma core. The RF optics aims at guiding the plasma emission signal to the antenna array. To meet different physical requirements, three types of field of view have been achieved for the plasma imaging, with zoom factors of around 1, 1.5 and 2, respectively. The focal surfaces are almost flat, with a maximum off-mapping (defined as the radial distance between the beam waists of the lower-/uppermost antennas and electron cyclotron emission layer) less than 2.5 cm, which can match the electron cyclotron emission layer quite well and suppress the image distortion in the plasma edge region. Furthermore, the impact of possible vibrations and installation error on the focal plane has been evaluated. In addition, the predefined MHD and turbulence perturbations are well reproduced by combining the optical simulation results and synthetic ECEI modeling, which further verifies the good performance of the RF optics.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1986

Cryogenic star-tracking telescope for Gravity Probe B

This paper describes the design, development and preliminary testing of the cryogenic star-tracking telescope used as an optical reference for the gyroscopes in the Gravity Probe B Relativity Gyroscope experiment. The telescope is operated at 1.8 K; it is fabricated entirely from fused quartz components held together by optical contacting; it has a physical length of 14 in., a focal length of 150 in. and an aperture of 5.6 in. Readout is by two photomultiplier chopper-detector assemblies at ambient satellite temperature. When fully operational, the telescope may be expected to have a precision approaching 0.1 milliarcsec over a linear range of 70 + or 70 milliarcsec. Its projected noise performance corresponds to an angular resolution of 1 milliarcsec in 1 Hz bandwidth. The paper includes a theoretical analysis, a description of the design and fabrication of a laboratory version of the telescope, a discussion of techniques of optical contacting, an account of vibration tests on a separate mass model of the telescope, a description of the artificial star developed for optical tests, and an account of preliminary experimental results.

Everitt, C. W. F.↗
DOE OSTI2026

A simplified di-homodyne transient grating spectroscopy system utilizing polarization

Here, a modification to the di-homodyne transient grating spectroscopy optical arrangement is presented that removes the need to individually align two spatially separated probe laser beams. This work details the novel application of a single probe beam that utilizes birefringent materials to produce two optically homodyned signals with a relative phase shift of π radians. This arrangement effectively simplifies the alignment to one probe beam and removes the relative phase shift ambiguity between each homodyned signal. Several example measurements for tungsten, titanium, molybdenum, and silicon are shown to illustrate the utility of the new optical system.

Simmonds, M. J. [Univ. of California, San Diego, C↗
DOE OSTI2023

Probing the atomically diffuse interfaces in Pd@Pt core-shell nanoparticles in three dimensions

Deciphering the three-dimensional atomic structure of solid-solid interfaces in core-shell nanomaterials is the key to understand their catalytical, optical and electronic properties. Here, we probe the three-dimensional atomic structures of palladium-platinum core-shell nanoparticles at the single-atom level using atomic resolution electron tomography. We quantify the rich structural variety of core-shell nanoparticles with heteroepitaxy in 3D at atomic resolution. Instead of forming an atomically-sharp boundary, the core-shell interface is found to be atomically diffuse with an average thickness of 4.2 Å, irrespective of the particle’s morphology or crystallographic texture. The high concentration of Pd in the diffusive interface is highly related to the free Pd atoms dissolved from the Pd seeds, which is confirmed by atomic images of Pd and Pt single atoms and sub-nanometer clusters using cryogenic electron microscopy. These results advance our understanding of core-shell structures at the fundamental level, providing potential strategies into precise nanomaterial manipulation and chemical property regulation.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2015

Spatially resolved electron density and electron energy distribution function in Ar magnetron plasmas used for sputter-deposition of ZnO-based thin films

Langmuir probe and trace rare gases optical emission spectroscopy were used to analyze the spatial structure of the electron density and electron energy distribution function (EEDF) in a cylindrical Ar magnetron plasma reactor used for sputter-deposition of ZnO-based thin films. While a typical Bessel (zero order) diffusion profile was observed along the radial direction for the number density of charged particles at 21 cm from the ZnO target, a significant rise of these populations with respect to the Bessel function was seen in the center of the reactor at 4 cm from the magnetron surface. As for the EEDF, it was found to transform from a more or less Maxwellian far from the target to a two-temperature Maxwellian with a depletion of high-energy electrons where magnetic field confinement effects become important. No significant change in the behavior of the electron density and EEDF across a wide range of pressures (5–100 mTorr) and self-bias voltages (115–300 V) was observed during magnetron sputtering of Zn, ZnO, and In{sub 2}O{sub 3} targets. This indicates that sputtering of Zn, In, and O atoms do not play a very significant role on the electron particle balance and electron heating dynamics, at least over the range of experimental conditions investigated.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗