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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 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Attainment of a 40 TW peak output power with a visible-range hybrid femtosecond laser system

We report the results of investigations aimed at raising the peak output power of a THL-100 visible-range hybrid femtosecond laser system based on a XeF(C − A) photodissociation amplifier. The increase in power was achieved due to the shortening of the pulse duration at the system output by broadening the spectral profile of the second harmonic from 5.3 to 8 nm, which takes place in the transformation of a negatively chirped pulse of the fundamental frequency radiation in a nonlinear KDP crystal. After the KDP the radiation pulse was stretched to 1.8 ps in a prism stretcher and amplified in the XeF(C − A) amplifier. The energy obtained at the amplifier output was 1.2 J. After compression of the amplified output pulse, its duration was equal to 29.4 fs, which means that a peak output power of 40 TW was reached at the output of the laser system. (lasers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Influence of birefringent fibre joints on the visibility drift in a Mach – Zehnder interferometer

It is shown that imperfect joints of linear birefringent fibres in a fibre interferometer may result in an uncontrolled visibility drift under varying environmental conditions even with a standard phase matching device. As an example, a double Mach – Zehnder interferometer is considered, which is employed in schemes of quantum key distribution. Results of numerical simulation demonstrate the standard deviation of the quantum bit error rate (QBER), which is comparable to an average QBER value. (paper)

36 MATERIALS SCIENCE↗
DOE OSTI2015

Visible photoelectrochemical water splitting into H 2 and O 2 in a dye-sensitized photoelectrosynthesis cell

A hybrid strategy for solar water splitting is exploited here based on a dye-sensitized photoelectrosynthesis cell (DSPEC) with a mesoporous SnO 2 /TiO 2 core/shell nanostructured electrode derivatized with a surface-bound Ru(II) polypyridyl-based chromophore–catalyst assembly. The assembly, [(4,4’-(PO 3 H 2 ) 2 bpy) 2 Ru(4-Mebpy-4’-bimpy)Ru(tpy)(OH 2 )] 4+ ([RuaII-RubII-OH 2 ] 4+ , combines both a light absorber and a water oxidation catalyst in a single molecule. It was attached to the TiO 2 shell by phosphonate-surface oxide binding. The oxide-bound assembly was further stabilized on the surface by atomic layer deposition (ALD) of either Al 2 O 3 or TiO 2 overlayers. Illumination of the resulting fluorine-doped tin oxide (FTO)|SnO 2 /TiO 2 |-[Ru a II -Ru b II -OH 2 ] 4+ (Al 2 O 3 or TiO 2 ) photoanodes in photoelectrochemical cells with a Pt cathode and a small applied bias resulted in visible-light water splitting as shown by direct measurements of both evolved H 2 and O 2 . The performance of the resulting DSPECs varies with shell thickness and the nature and extent of the oxide overlayer. Use of the SnO 2 /TiO 2 core/shell compared with nanoITO/TiO 2 with the same assembly results in photocurrent enhancements of ~5. In conclusion, systematic variations in shell thickness and ALD overlayer lead to photocurrent densities as high as 1.97 mA/cm 2 with 445-nm, ~90-mW/cm 2 illumination in a phosphate buffer at pH 7.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Diamond surface functionalization via visible light–driven C–H activation for nanoscale quantum sensing

Nitrogen-vacancy (NV) centers in diamond are a promising platform for nanoscale NMR sensing. Despite significant progress toward using NV centers to detect and localize nuclear spins down to the single spin level, NV-based spectroscopy of individual, intact, arbitrary target molecules remains elusive. Such sensing requires that target molecules are immobilized within nanometers of NV centers with long spin coherence. The inert nature of diamond typically requires harsh functionalization techniques such as thermal annealing or plasma processing, limiting the scope of functional groups that can be attached to the surface. Solution-phase chemical methods can be readily generalized to install diverse functional groups, but they have not been widely explored for single-crystal diamond surfaces. Moreover, realizing shallow NV centers with long spin coherence times requires highly ordered single-crystal surfaces, and solution-phase functionalization has not yet been shown with such demanding conditions. In this work, we report a versatile strategy to directly functionalize C–H bonds on single-crystal diamond surfaces under ambient conditions using visible light, forming C–F, C–Cl, C–S, and C–N bonds at the surface. This method is compatible with NV centers within 10 nm of the surface with spin coherence times comparable to the state of the art. As a proof-of-principle demonstration, we use shallow ensembles of NV centers to detect nuclear spins from surface-bound functional groups. Our approach to surface functionalization opens the door to deploying NV centers as a tool for chemical sensing and single-molecule spectroscopy.

Science & Technology - Other Topics↗
DOE OSTI2013

DIFFRACTION-LIMITED VISIBLE LIGHT IMAGES OF ORION TRAPEZIUM CLUSTER WITH THE MAGELLAN ADAPTIVE SECONDARY ADAPTIVE OPTICS SYSTEM (MagAO)

We utilized the new high-order (250-378 mode) Magellan Adaptive Optics system (MagAO) to obtain very high spatial resolution observations in ''visible light'' with MagAO's VisAO CCD camera. In the good-median seeing conditions of Magellan (0.''5-0.''7), we find MagAO delivers individual short exposure images as good as 19 mas optical resolution. Due to telescope vibrations, long exposure (60 s) r' (0.63 {mu}m) images are slightly coarser at FWHM = 23-29 mas (Strehl {approx}28%) with bright (R < 9 mag) guide stars. These are the highest resolution filled-aperture images published to date. Images of the young ({approx}1 Myr) Orion Trapezium {theta}{sup 1} Ori A, B, and C cluster members were obtained with VisAO. In particular, the 32 mas binary {theta}{sup 1} Ori C{sub 1} C{sub 2} was easily resolved in non-interferometric images for the first time. The relative positions of the bright trapezium binary stars were measured with {approx}0.6-5 mas accuracy. We are now sensitive to relative proper motions of just {approx}0.2 mas yr{sup -1} ({approx}0.4 km s{sup -1} at 414 pc)-this is a {approx}2-10 Multiplication-Sign improvement in orbital velocity accuracy compared to previous efforts. For the first time, we see clear motion of the barycenter of {theta}{sup 1} Ori B{sub 2} B{sub 3} about {theta}{sup 1} Ori B{sub 1}. All five members of the {theta}{sup 1} Ori B system appear likely to be a gravitationally bound ''mini cluster'', but we find that not all the orbits can be both circular and co-planar. The lowest mass member of the {theta}{sup 1} Ori B system (B{sub 4}; mass {approx}0.2 M{sub Sun }) has a very clearly detected motion (at 4.1 {+-} 1.3 km s{sup -1}; correlation = 99.9%) w.r.t. B{sub 1}. Previous work has suggested that B{sub 4} and B{sub 3} are on long-term unstable orbits and will be ejected from this ''mini cluster''. However, our new ''baseline'' model of the {theta}{sup 1} Ori B system suggests a more hierarchical system than previously thought, and so the ejection of B{sub 4} may not occur for many orbits, and B{sub 3} may be stable against ejection in the long-term. This ''ejection'' process of the lowest mass member of a ''mini cluster'' could play a major role in the formation of low-mass stars and brown dwarfs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

PHOTOMETRIC TRENDS IN THE VISIBLE SOLAR CONTINUUM AND THEIR SENSITIVITY TO THE CENTER-TO-LIMB PROFILE

Solar irradiance variations over solar rotational timescales are largely determined by the passage of magnetic structures across the visible solar disk. Variations on solar cycle timescales are thought to be similarly due to changes in surface magnetism with activity. Understanding the contribution of magnetic structures to total solar irradiance and solar spectral irradiance requires assessing their contributions as a function of disk position. Since only relative photometry is possible from the ground, the contrasts of image pixels are measured with respect to a center-to-limb intensity profile. Using nine years of full-disk red and blue continuum images from the Precision Solar Photometric Telescope at the Mauna Loa Solar Observatory, we examine the sensitivity of continuum contrast measurements to the center-to-limb profile definition. Profiles which differ only by the amount of magnetic activity allowed in the pixels used to determine them yield oppositely signed solar cycle length continuum contrast trends, either agreeing with previous results and showing negative correlation with solar cycle or disagreeing and showing positive correlation with solar cycle. Changes in the center-to-limb profile shape over the solar cycle are responsible for the contradictory contrast results, and we demonstrate that the lowest contrast structures, internetwork and network, are most sensitive to these. Thus the strengths of the full-disk, internetwork, and network photometric trends depend critically on the magnetic flux density used in the quiet-Sun definition. We conclude that the contributions of low contrast magnetic structures to variations in the solar continuum output, particularly to long-term variations, are difficult, if not impossible, to determine without the use of radiometric imaging.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

First measurement of S/XB values of Re I visible emission lines

A spectroscopic parameter, so called S/XB (the number of ionization events per photon or inverse photon efficiency), is experimentally determined for Re I visible emission lines (488.9, 527.1, and 527.6 nm) at an electron temperature range of ~2–8 eV in the PISCES-B linear plasma device. Our standard mass loss method was applied, where a pure Re sample was sputtered by Ar plasma. In addition, a new alloy method was developed, where a W-3.3 at% Re alloy sample was used. In the new method, the sputtered flux ratio of Re and W atoms is assumed to be the same as the elemental composition because of the very similar sputtering yields. In this work, good agreement in measured Re I S/XB values is obtained between the standard mass loss and new alloy methods.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Visible emission spectra of thermographic phosphors under x-ray excitation

Thermographic phosphors have been employed for temperature sensing in challenging environments, such as on surfaces or within solid samples exposed to dynamic heating, because of the high temporal and spatial resolution that can be achieved using this approach. Typically, UV light sources are employed to induce temperature-sensitive spectral responses from the phosphors. However, it would be beneficial to explore x-rays as an alternate excitation source to facilitate simultaneous x-ray imaging of material deformation and temperature of heated samples and to reduce UV absorption within solid samples being investigated. Here, the phosphors BaMgAl 10 O 17 :Eu (BAM), Y 2 SiO 5 :Ce, YAG:Dy, La 2 O 2 S:Eu, ZnGa 2 O 4 :Mn, Mg 3 F 2 GeO 4 :Mn, Gd 2 O 2 S:Tb, and ZnO were excited using incident synchrotron x-ray radiation. These materials were chosen to include conventional thermographic phosphors as well as x-ray scintillators (with crossover between these two categories). X-ray-induced thermographic behavior was explored through the measurement of visible spectral response with varying temperature. The incident x-rays were observed to excite the same electronic energy level transitions in these phosphors as UV excitation. Similar shifts in the spectral response of BAM, Y 2 SiO 5 :Ce, YAG:Dy, La 2 O 2 S:Eu, ZnGa 2 O 4 :Mn, Mg 3 F 2 GeO 4 :Mn, and Gd 2 O 2 S:Tb were observed when compared to their response to UV excitation found in literature. Some phosphors were observed to thermally quench in the temperature ranges tested here, while the response from others did not rise above background noise levels. This may be attributed to the increased probability of non-radiative energy release from these phosphors due to the high energy of the incident x-rays. These results indicate that x-rays can serve as a viable excitation source for phosphor thermometry.

42 ENGINEERING↗
DOE OSTI2021

Metallic and porous Ti nanorod arrays for visible-IR light absorption and dendrite-free stable lithium-metal batteries

It is still a challenging task to prepare highly porous nanorod arrays of metals formed on substrates for optical and energy storage applications. Herein, we demonstrate the design and synthesis of black color, metallic and highly porous Ti nanorod arrays as novel current collectors for dendrite-free and highly stable Li-metal anodes. The high porosity of metallic nanorod arrays provides numerous heterogeneous nucleation sites and huge contact area and large space for the accommodation of Li metal. The conductive metallic Ti nanorod arrays enhance electrode integration. Effectively, it eliminates formation Li dendrites and demonstrates superior cycling stability over 300 cycles. Additionally, the unique porous structures of the nanorod arrays can decrease the amplitude of forced vibration in narrow space leading to light absorption. Interestingly, the metal is black instead of metallic color. The black metallic nanorod arrays can absorb more than 96% of both visible and infra-red lights. Furthermore, this black color metallic porous nanorod arrays may find additional applications in aerospace, energy, biomedical, defence, and chemical industries.

25 ENERGY STORAGE↗
DOE OSTI2021

Visible spectroscopy of highly charged tungsten ions with the JET charge exchange diagnostic

Since the installation of the ITER-like wall on the JET tokamak, visible emission from a broad range of tungsten charge states has complicated plasma ion temperature and toroidal rotation measurements. A plethora of charge exchange transitions, from ions up to W 56+ , and 21 suspected magnetic dipole transitions have been observed. In particular W 39+ and W 46+ charge exchange emission contaminates the long-established carbon measurement at 529 nm. Fortunately the wavelength and relative intensity of the tungsten charge exchange lines is predictable and their influence can be mitigated when they are included in the spectral fit. Neon based charge exchange measurements at 525 nm are now preferred on JET since the ITER-like wall, however in this case an unidentified tungsten magnetic dipole transition contaminates the spectrum when the electron temperature is low.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Dependence of polytetrafluoroethylene reflectance on thickness at visible and ultraviolet wavelengths in air

Polytetrafluoroethylene (PTFE) is an excellent diffuse reflector widely used in light collection systems for particle physics experiments. However, the reflectance of PTFE is a function of its thickness. Here, in this work, we investigate this dependence in air for light of wavelengths 260 nm and 450 nm using two complementary methods. We find that PTFE reflectance for thicknesses from 5 mm to 10 mm ranges from 92.5% to 94.5% at 450 nm, and from 90.0% to 92.0% at 260 nm. We also see that the reflectance of PTFE of a given thickness can vary by as much as 2.7% within the same piece of material. Finally, we show that placing a specular reflector behind the PTFE can recover the loss of reflectance in the visible without introducing a specular component in the reflectance.

47 OTHER INSTRUMENTATION↗
DOE OSTI2013

ABSORPTIONS IN THE VISIBLE OF PROTONATED PYRENE COLLISIONALLY COOLED TO 15 K

Protonated polycyclic hydrocarbons have been added to the list of suggested carriers of diffuse interstellar absorptions. To test this proposition requires laboratory spectra measured under interstellar conditions, in particular with the rotational and vibrational degrees of freedom equilibrated to low temperatures. This has been achieved for protonated pyrene with absorption bands in the visible, using an ion trap and collisional cooling to ≈15 K. A two-photon excitation-dissociation scheme was employed to record the (1) {sup 1} A' ← X {sup 1} A' electronic spectrum on around 10{sup 5} ions per duty cycle. The origin band of the absorption spectrum of this relatively large polycyclic aromatic species with 27 atoms is located at 4858.86 Å. Two further comparably intense spectral features are present at 4834.48 and 4809.32 Å. This is one of the largest protonated aromatics studied in the gas phase and compared to astronomical observations; however, it is not a carrier of known diffuse interstellar bands.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2015

Characterizing visible and invisible cell wall mutant phenotypes

About 10% of a plant's genome is devoted to generating the protein machinery to synthesize, remodel, and deconstruct the cell wall. High-throughput genome sequencing technologies have enabled a reasonably complete inventory of wall-related genes that can be assembled into families of common evolutionary origin. Assigning function to each gene family member has been aided immensely by identification of mutants with visible phenotypes or by chemical and spectroscopic analysis of mutants with ‘invisible’ phenotypes of modified cell wall composition and architecture that do not otherwise affect plant growth or development. This review connects the inference of gene function on the basis of deviation from the wild type in genetic functional analyses to insights provided by modern analytical techniques that have brought us ever closer to elucidating the sequence structures of the major polysaccharide components of the plant cell wall.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Comparison of continuum-continuum and Coulomb-laser-coupling delays from visible to midinfrared wavelengths

We compare the various proposed formulas for CLC and CC delays using analytical and numerical methods across a range of wavelengths spanning visible to midinfrared. We show that one of the CC definitions is nearly equal to the CLC delay over a range of photoelectron energies and wavelengths. We furthermore obtain alternate expressions for the CC delays. These expressions are simpler to use and show close correspondence to the CLC delays. Based on this correspondence, we suggest a correction to the CLC delay for low-energy electrons, where the currently used approximation breaks down. Our work provides guidance for when it is valid to treat CC and CLC delays as being equivalent.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2021

Second-order nonlinear optical and linear ultraviolet-visible absorption properties of the type-II multiferroic candidates RbFe( A O 4 ) 2 ( A = Mo, Se, S)

Motivated by the search for type-II multiferroics, in this work, we present a comprehensive optical study of a complex oxide family of type-II multiferroic candidates: RbFe(MoO 4 ) 2 , RbFe(SeO 4 ) 2 , and RbFe(SO 4 ) 2 .We employ rotationalanisotropy second harmonic generation spectroscopy (RA SHG), a technique sensitive to point symmetries, to address discrepancies in literature-assigned point/space groups and to identify the correct crystal structures. At room temperature we find that our RA SHG patterns rotate away from the crystal axes in RbFe(AO 4 ) 2 ( A = Se, S), which identifies the lack of mirror symmetry and in-plane two-fold rotational symmetry. Also, the SHG efficiency of RbFe(SeO 4 ) 2 is two orders of magnitude stronger than RbFe(AO 4 )2 ( A = Mo, S), which suggests broken inversion symmetry. Additionally, we present temperature-dependent linear optical characterizations near the band edge of this family of materials using ultraviolet-visible absorption spectroscopy. Included is experimental evidence of the band gap energy and band gap transition type for this family. Subband gap absorption is also presented, which reveals prominent optical transitions, some with an unusual central energy temperature dependence. Furthermore, we find that by substituting the A site in RbFe(AO 4 ) 2 ( A = Mo, Se, S), the aforementioned transitions are spectrally tunable. Finally, we discuss the potential origin and impact of these tunable transitions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Photonics Breakthroughs 2024: Narrow-Linewidth Lasers in the Visible and Near-Infrared

Narrow-linewidth lasers enable a variety of high-precision applications, such as sensing, optical clocks, and microwave frequency generation. Advances in photonic integration in the last decade led to the development of ultra-low-noise integrated semiconductor lasers, mostly in the telecom wavelength range. In recent years, the demand for high-performance lasers at shorter wavelengths skyrocketed, driven by applications in sensing and atom trapping. Low-noise lasers are of particular importance in this spectral range, as they are essential for optical clocks. Here, we will review recent progress in narrow-linewidth lasers at shorter wavelengths, present results on a hybrid-integrated low-noise laser at 780 nm and discuss the perspectives and challenges of high-performance semiconductor lasers in the visible and near-infrared.

Prokoshin, Artem [King Abdullah University of Scie↗
DOE OSTI2023

Development of a Low-Cost, Sensitivity-Optimized Fluorescence Sensor for Visible Spectrum Analysis

This paper presents an economically viable, sensitivity-optimized fluorescence sensor for detecting low concentrations of fluorophores in the visible spectrum range. The sensor employs a deep ultraviolet (DUV) 275-nm LED and a dichroic mirror to establish a co-axial optical path for excitation and emission. Instead of utilizing a general-purposed spectrometer optimized for high spectral resolution, the sensor strikes a balance between resolution and sensitivity by using an appropriate aperture size and optimized optical design tailored for the spectral characteristics of fluorophores. Here, the manuscript demonstrates measurements of ppb-level rare earth element (REE) samples containing terbium (Tb), europium (Eu), dysprosium (Dy), and samarium (Sm) in aqueous solutions. Through balanced design that optimizes collection of fluorescence emission without losing spectral information, this work shows the feasibility of developing a low-cost, compact, and highly sensitive fluorescence sensors with improved detection sensitivity when compared to bench-top commercial spectrofluorometers at far higher costs.

47 OTHER INSTRUMENTATION↗
DOE OSTI2023

A Hierarchical Control Architecture: Utilization of Behind-the-Meter Appliances with Increased Visibility and Controllability

Optimal operations of distribution systems to enhance reliability and resiliency can be achieved if information with higher fidelity can be accessed from grid premise devices. This paper discusses a hierarchical control architecture that can introduce higher visibility and controllability by utilizing the estimated injection and absorption of different behind-the-meter controllable loads, and DERs, including EVs, within a premise. The acquired information is used to make control decisions for scheduling the premise appliances to reduce energy consumptions. The premise controller can also optimize the consumptions on a day-to-day basis in addition to taking input signals from the utility operators to support grid-service events (e.g., peak shaving). The entire control architecture is designed in a modular and scalable fashion that provides benefits to the utility from the reuse of existing infrastructure while creating opportunities for various grid services to be enabled by the operation of premise controllers.

24 POWER TRANSMISSION AND DISTRIBUTION↗