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Results for “VISIBLE SPECTRA”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,495 records · Page 83
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Effect of Ti seed layers on structure of self-organized epitaxial face-centered-cubic-Ag(001) oriented nanodots

The influence of Ti seed layers on the structure of self-organized Ag nanodots, obtained with a Ti seed-layer-assisted thermal agglomeration method, has been investigated. The samples were grown on MgO(001) single crystal substrates by RF magnetron sputter deposition. The samples were deposited at room temperature and post-annealed at 350 °C for 4 h while maintaining the chamber vacuum conditions. The results of atomic force microscopy (AFM) observations indicated that the insertion of the Ti seed layer (0.6–5.0 nm) between the MgO substrate and Ag layer promotes the agglomeration process, forming the nanodot array. Comparisons between the AFM images revealed that the size of the Ag nanodots was increased with an increase in the Ti seed layer thickness. The atomic concentration of the film surface was confirmed by X-ray photoelectron spectroscopy (XPS). The XPS result suggested that the nanodot surface mainly consisted of Ag. Moreover, X-ray diffraction results proved that the initial deposition of the Ti seed layer (0.6–5.0 nm) onto MgO(001) prior to the Ag deposition yielded high-quality fcc-Ag(001) oriented epitaxial nanodots. The optical absorbance spectra of the fabricated Ag nanodots with various Ti seed layer thicknesses were obtained in the visible light range.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Electronic and intraband optical properties of single quantum rings under intense laser field radiation

The influence of an intense laser field on one-electron states and intraband optical absorption coefficients is investigated in two-dimensional GaAs/Ga{sub 0.7}Al{sub 0.3}As quantum rings. An analytical expression of the effective lateral confining potential induced by the laser field is obtained. The one-electron energy spectrum and wave functions are found using the effective mass approximation and exact diagonalization technique. We have shown that changes in the incident light polarization lead to blue- or redshifts in the intraband optical absorption spectrum. Moreover, we found that only blueshift is obtained with increasing outer radius of the quantum ring.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Preparation and characterization of solar exfoliated graphene

Hummer's method was used for the chemical synthesis of graphite oxide from graphite flakes. Simultaneous exfoliation and reduction of graphite oxide to Graphene was achieved through focused solar light irradiation using a convex lens. The morphological characteristics were studied using SEM and TEM. Layered morphology of Graphene was observed through TEM. Raman spectra and FTIR were used for the structural characterization of Graphene. EDAX analysis showed the drop in oxygen content during exfoliation. The method offered a faster, easier and environmental friendly method to produce Graphene for potential applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Two-dimensional electronic spectroscopy with birefringent wedges

We present a simple experimental setup for performing two-dimensional (2D) electronic spectroscopy in the partially collinear pump-probe geometry. The setup uses a sequence of birefringent wedges to create and delay a pair of phase-locked, collinear pump pulses, with extremely high phase stability and reproducibility. Continuous delay scanning is possible without any active stabilization or position tracking, and allows to record rapidly and easily 2D spectra. The setup works over a broad spectral range from the ultraviolet to the near-IR, it is compatible with few-optical-cycle pulses and can be easily reconfigured to two-colour operation. A simple method for scattering suppression is also introduced. As a proof of principle, we present degenerate and two-color 2D spectra of the light-harvesting complex 1 of purple bacteria.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Transient electrically detected magnetic resonance spectroscopy applied to organic solar cells

The influence of light-induced paramagnetic states on the photocurrent generated by polymer:fullerene solar cells is studied using spin-sensitive techniques in combination with laser-flash excitation. For this purpose, we developed a setup that allows for simultaneous detection of transient electron paramagnetic resonance as well as transient electrically detected magnetic resonance (trEDMR) signals from fully processed and encapsulated solar cells. Combining both techniques provides a direct link between photoinduced triplet excitons, charge transfer states, and free charge carriers as well as their influence on the photocurrent generated by organic photovoltaic devices. Our results obtained from solar cells based on poly(3-hexylthiophene) as electron donor and a fullerene-based electron acceptor show that the resonant signals observed in low-temperature (T = 80 K) trEDMR spectra can be attributed to positive polarons in the polymer as well as negative polarons in the fullerene phase, indicating that both centers are involved in spin-dependent processes that directly influence the photocurrent.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Prediction of transmittance spectra for transparent composite electrodes with ultra-thin metal layers

Recent interest in indium-free transparent composite-electrodes (TCEs) has motivated theoretical and experimental efforts to better understand and enhance their electrical and optical properties. Various tools have been developed to calculate the optical transmittance of multilayer thin-film structures based on the transfer-matrix method. However, the factors that affect the accuracy of these calculations have not been investigated very much. In this study, two sets of TCEs, TiO{sub 2}/Au/TiO{sub 2} and TiO{sub 2}/Ag/TiO{sub 2}, were fabricated to study the factors that affect the accuracy of transmittance predictions. We found that the predicted transmittance can deviate significantly from measured transmittance for TCEs that have ultra-thin plasmonic metal layers. The ultrathin metal layer in the TCE is typically discontinuous. When light interacts with the metallic islands in this discontinuous layer, localized surface plasmons are generated. This causes extra light absorption, which then leads to the actual transmittance being lower than the predicted transmittance.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

A spatial light modulator that uses scattering in a cholesteric liquid crystal

When a cholesteric liquid crystal (helical pitch: 5 μm) was sandwiched between two glass plates with no alignment coating (gap: 20 μm), a random-domain texture appeared and a strong light scattering took place. This translucent texture turned to a transparent homeotropic phase when an electric voltage of 20 V was applied to the liquid crystal layer. This phase transition was used for constructing a spatial light modulator that needed no polarizers. Indium-tin-oxide electrodes (0.8 mm square) were arranged on a glass substrate to create a 20 × 20 pixel array (20 mm square). The liquid crystal was injected into a gap (20 μm thickness) between this substrate and another glass plate with a uniform electrode (ground). The transmittance of the pixels was originally below 10% and decreased to 0% by 7 V application because of increase in the scattering loss. As the voltage was raised, the transmittance increased gradually in the 7–17 V range and then rapidly in the 17–20 V range, attaining 40% at 27 V. Various transmittance distributions or gray-scale images were attainable by applying a suitable voltage (7–27 V) to each pixel. The transmission range of this spatial light modulator extended from ultraviolet (350 nm) to infrared wavelengths (>800 nm). Owing to this wide transmission range as well as capability of the polarizer-free operation, this spatial light modulator is useful to control a lamp spectrum in spectroscopic measurements.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

ZnO nanoparticles obtained by ball milling technique: Structural, micro-structure, optical and photo-catalytic properties

The ZnO nanoparticles were obtained by ball milling of commercial grade ZnO powder at 250 rpm for 20 h and studied their structural, micro-structure, optical and photo-catalytic properties. Due to ball milling significant decrease in lattice parameters and average crystalline size is noticed for the as-milled ZnO nano powder. The HRSEM images of the as-milled powder consist of agglomerated fine spherical nanoparticles in the range of ~10-20 nm. The room temperature PL spectrum of as-milled ZnO nano powder excited under 320 nm reveals two emission bands at ~406 nm (violet emission) and ~639 nm (green emission). Interestingly about 98 % of photo degradation of methylene (MB) by the ZnO catalyst is achieved at 100 minutes of solar light irradiation.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

Atom femtosecond optical trap based on spectrally filtered laser radiation

We have examined the use of alkali metal (rubidium) vapour for spectral filtering of broadband pulsed laser light that is used to produce a femtosecond pulsed optical dipole trap. It has been shown that, even at large detuning of the centre emission frequency from the frequency of atomic transitions, spectral components present in the wings of the laser emission line are capable of heating localised atoms, thus reducing their lifetime in the atomic trap. Using atomic vapour for filtering the laser emission spectrum, we have suppressed its spectral components resulting in heating. This has made it possible to increase the lifetime of atoms in the pulsed optical dipole trap to a value comparable to their lifetime in an optical trap formed by narrow-band cw laser light. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

RX GEMINORUM: PHOTOMETRIC SOLUTIONS, (NEARLY UNIFORM) GAINER ROTATION, DONOR RADIAL VELOCITY SOLUTION, NON-LTE ACCRETION DISK MODELS OF Hα EMISSION PROFILES, AND SECULAR LIGHT CURVE CHANGES IN THE 20TH CENTURY

We obtained full-orbit Iybvu intermediate-band photometry and CCD spectroscopy of the long-period Algol eclipsing binary RX Geminorum. Photometric solutions using the Wilson–Devinney code give a gainer rotation (hotter, mass-accreting component) about 15 times the synchronous rate. We describe a simple technique to detect departures from uniform rotation of the hotter component. These binaries radiate double-peaked Hα emission from a low-mass accretion disk around the gainer. We used an approximate non-LTE disk code to predict models in fair agreement with observations, except in the far wings of the emission profile, where the star–inner disk boundary layer emits extra radiation. Variations in Hα emission derive from modulations in the transfer rate. A study of times of minima during the 20th century suggests that a perturbing third body is present near RX Gem.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

MULTI-WAVELENGTH OBSERVATIONS OF SUPERNOVA 2011ei: TIME-DEPENDENT CLASSIFICATION OF TYPE IIb AND Ib SUPERNOVAE AND IMPLICATIONS FOR THEIR PROGENITORS

We present X-ray, UV/optical, and radio observations of the stripped-envelope, core-collapse supernova (SN) 2011ei, one of the least luminous SNe IIb or Ib observed to date. Our observations begin with a discovery within {approx}1 day of explosion and span several months afterward. Early optical spectra exhibit broad, Type II-like hydrogen Balmer profiles that subside rapidly and are replaced by Type Ib-like He-rich features on a timescale of one week. High-cadence monitoring of this transition suggests absorption attributable to a high-velocity ({approx}> 12, 000 km s{sup -1}) H-rich shell, which is likely present in many Type Ib events. Radio observations imply a shock velocity of v Almost-Equal-To 0.13 c and a progenitor star average mass-loss rate of M-dot {approx}1.4 Multiplication-Sign 10{sup -5} M{sub sun} yr{sup -1} (assuming wind velocity v{sub w} = 10{sup 3} km s{sup -1}). This is consistent with independent constraints from deep X-ray observations with Swift-XRT and Chandra. Overall, the multi-wavelength properties of SN 2011ei are consistent with the explosion of a lower-mass (3-4 M{sub Sun }), compact (R{sub *} {approx}< 1 Multiplication-Sign 10{sup 11} cm), He-core star. The star retained a thin hydrogen envelope at the time of explosion, and was embedded in an inhomogeneous circumstellar wind suggestive of modest episodic mass loss. We conclude that SN 2011ei's rapid spectral metamorphosis is indicative of time-dependent classifications that bias estimates of the relative explosion rates for Type IIb and Ib objects, and that important information about a progenitor star's evolutionary state and mass loss immediately prior to SN explosion can be inferred from timely multi-wavelength observations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

DISCOVERY OF THE BROAD-LINED TYPE Ic SN 2013cq ASSOCIATED WITH THE VERY ENERGETIC GRB 130427A

Long-duration gamma-ray bursts (GRBs) at z < 1 are found in most cases to be accompanied by bright, broad-lined Type Ic supernovae (SNe Ic-BL). The highest-energy GRBs are mostly located at higher redshifts, where the associated SNe are hard to detect observationally. Here, we present early and late observations of the optical counterpart of the very energetic GRB 130427A. Despite its moderate redshift, z = 0.3399 ± 0.0002, GRB 130427A is at the high end of the GRB energy distribution, with an isotropic-equivalent energy release of E{sub iso} ∼ 9.6 × 10{sup 53} erg, more than an order of magnitude more energetic than other GRBs with spectroscopically confirmed SNe. In our dense photometric monitoring, we detect excess flux in the host-subtracted r-band light curve, consistent with that expected from an emerging SN, ∼0.2 mag fainter than the prototypical SN 1998bw. A spectrum obtained around the time of the SN peak (16.7 days after the GRB) reveals broad undulations typical of SNe Ic-BL, confirming the presence of an SN, designated SN 2013cq. The spectral shape and early peak time are similar to those of the high expansion velocity SN 2010bh associated with GRB 100316D. Our findings demonstrate that high-energy, long-duration GRBs, commonly detected at high redshift, can also be associated with SNe Ic-BL, pointing to a common progenitor mechanism.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

M dwarf metallicities and giant planet occurrence: Ironing out uncertainties and systematics

Comparisons between the planet populations around solar-type stars and those orbiting M dwarfs shed light on the possible dependence of planet formation and evolution on stellar mass. However, such analyses must control for other factors, i.e., metallicity, a stellar parameter that strongly influences the occurrence of gas giant planets. We obtained infrared spectra of 121 M dwarfs stars monitored by the California Planet Search and determined metallicities with an accuracy of 0.08 dex. The mean and standard deviation of the sample are –0.05 and 0.20 dex, respectively. We parameterized the metallicity dependence of the occurrence of giant planets on orbits with a period less than two years around solar-type stars and applied this to our M dwarf sample to estimate the expected number of giant planets. The number of detected planets (3) is lower than the predicted number (6.4), but the difference is not very significant (12% probability of finding as many or fewer planets). The three M dwarf planet hosts are not especially metal rich and the most likely value of the power-law index relating planet occurrence to metallicity is 1.06 dex per dex for M dwarfs compared to 1.80 for solar-type stars; this difference, however, is comparable to uncertainties. Giant planet occurrence around both types of stars allows, but does not necessarily require, a mass dependence of ∼1 dex per dex. The actual planet-mass-metallicity relation may be complex, and elucidating it will require larger surveys like those to be conducted by ground-based infrared spectrographs and the Gaia space astrometry mission.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

The SLUGGS survey: wide-field stellar kinematics of early-type galaxies

We present stellar kinematics of 22 nearby early-type galaxies (ETGs), based on two-dimensional (2D) absorption line stellar spectroscopy out to ∼2-4 R {sub e} (effective radii), as part of the ongoing SLUGGS Survey. The galaxies span a factor of 20 in intrinsic luminosity, as well as a full range of environment and ETG morphology. Our data consist of good velocity resolution (σ{sub inst} ∼ 25 km s{sup –1}) integrated stellar-light spectra extracted from the individual slitlets of custom made Keck/DEIMOS slitmasks. We extract stellar kinematics measurements (V, σ, h {sub 3}, and h {sub 4}) for each galaxy. Combining with literature values from smaller radii, we present 2D spatially resolved maps of the large-scale kinematic structure in each galaxy. We find that the kinematic homogeneity found inside 1 R {sub e} often breaks down at larger radii, where a variety of kinematic behaviors are observed. While central slow rotators remain slowly rotating in their halos, central fast rotators show more diversity, ranging from rapidly increasing to rapidly declining specific angular momentum profiles in the outer regions. There are indications that the outer trends depend on morphological type, raising questions about the proposed unification of the elliptical and lenticular (S0) galaxy families in the ATLAS{sup 3D} survey. Several galaxies in our sample show multiple lines of evidence for distinct disk components embedded in more slowly rotating spheroids, and we suggest a joint photometric-kinematic approach for robust bulge-disk decomposition. Our observational results appear generally consistent with a picture of two-phase (in-situ plus accretion) galaxy formation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

A continuum of H- to He-rich tidal disruption candidates with a preference for E+A galaxies

We present the results of a Palomar Transient Factory (PTF) archival search for blue transients that lie in the magnitude range between 'normal' core-collapse and superluminous supernovae (i.e., with –21 ≤ M {sub R} {sub (peak)} ≤ – 19). Of the six events found after excluding all interacting Type IIn and Ia-CSM supernovae, three (PTF09ge, 09axc, and 09djl) are coincident with the centers of their hosts, one (10iam) is offset from the center, and a precise offset cannot be determined for two (10nuj and 11glr). All the central events have similar rise times to the He-rich tidal disruption candidate PS1-10jh, and the event with the best-sampled light curve also has similar colors and power-law decay. Spectroscopically, PTF09ge is He-rich, while PTF09axc and 09djl display broad hydrogen features around peak magnitude. All three central events are in low star formation hosts, two of which are E+A galaxies. Our spectrum of the host of PS1-10jh displays similar properties. PTF10iam, the one offset event, is different photometrically and spectroscopically from the central events, and its host displays a higher star formation rate. Finding no obvious evidence for ongoing galactic nuclei activity or recent star formation, we conclude that the three central transients likely arise from the tidal disruption of a star by a supermassive black hole. We compare the spectra of these events to tidal disruption candidates from the literature and find that all of these objects can be unified on a continuous scale of spectral properties. The accumulated evidence of this expanded sample strongly supports a tidal disruption origin for this class of nuclear transients.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

KEPLER FLARES. II. THE TEMPORAL MORPHOLOGY OF WHITE-LIGHT FLARES ON GJ 1243

We present the largest sample of flares ever compiled for a single M dwarf, the active M4 star GJ 1243. Over 6100 individual flare events, with energies ranging from 10{sup 29} to 10{sup 33} erg, are found in 11 months of 1 minute cadence data from Kepler. This sample is unique for its completeness and dynamic range. We have developed automated tools for finding flares in short-cadence Kepler light curves, and performed extensive validation and classification of the sample by eye. From this pristine sample of flares we generate a median flare template. This template shows that two exponential cooling phases are present during the white-light flare decay, providing fundamental constraints for models of flare physics. The template is also used as a basis function to decompose complex multi-peaked flares, allowing us to study the energy distribution of these events. Only a small number of flare events are not well fit by our template. We find that complex, multi-peaked flares occur in over 80% of flares with a duration of 50 minutes or greater. The underlying distribution of flare durations for events 10 minutes and longer appears to follow a broken power law. Our results support the idea that sympathetic flaring may be responsible for some complex flare events.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

A HUBBLE DIAGRAM FROM TYPE II SUPERNOVAE BASED SOLELY ON PHOTOMETRY: THE PHOTOMETRIC COLOR METHOD

We present a Hubble diagram of SNe II using corrected magnitudes derived only from photometry, with no input of spectral information. We use a data set from the Carnegie Supernovae Project I for which optical and near-infrared light curves were obtained. The apparent magnitude is corrected by two observables, one corresponding to the slope of the plateau in the V band and the second a color term. We obtain a dispersion of 0.44 mag using a combination of the (V − i) color and the r band and we are able to reduce the dispersion to 0.39 mag using our golden sample. A comparison of our photometric color method (PCM) with the standardized candle method (SCM) is also performed. The dispersion obtained for the SCM (which uses both photometric and spectroscopic information) is 0.29 mag, which compares with 0.43 mag from the PCM for the same SN sample. The construction of a photometric Hubble diagram is of high importance in the coming era of large photometric wide-field surveys, which will increase the detection rate of supernovae by orders of magnitude. Such numbers will prohibit spectroscopic follow up in the vast majority of cases, and hence methods must be deployed which can proceed using solely photometric data.

79 ASTRONOMY AND ASTROPHYSICS↗