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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Effect of bath temperature on surface morphology and photocatalytic activity of ZnO nanorods

ZnO nanorods were prepared by using simple hydrothermal method using four different bath temperatures. All the prepared ZnO nanorods are annealed at 450°C and are characterized by using various techniques such as X-ray diffraction, UV spectra and scanning electron microscopy. Photocatalytic activity of the prepared ZnO nanorods is analyzed. A novel photocatalytic reactor designed with ZnO nanorods prepared at 90°C shows enhanced catalytic efficiency. The role of light irradiation time, bath temperature and surface morphology of the ZnO nanorods on the performance of photocatalytic reaction is analyzed.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Photoluminescence study of Mn doped ZnS nanoparticles prepared by co-precipitation method

ZnS nanoparticles co-doped with different concentration (5,10,15%) of Mn were synthesized using polyvinylpyrrolidone (PVP) as a capping agent under microwave irradiation. We confirmed doping of Mn in the host ZnS by EDAX whereas powder X-ray diffractogram showed the cubic zinc blende structure of all these samples. TEM images did showed agglomeration of particles and SAED pattern obtained indicated polycrystalline nature. From SAED pattern we calculated lattice parameter of the samples which have close resemblance from that obtained from XRD pattern. The band gap values of pure and doped ZnS nanoparticles were calculated from UV-Visible absorption spectra. ZnS itself is a luminescence material but when we dope it with transition metal ion such as Mn, Co, and Cu they exhibits strong and intense luminescence in the particular region. The photoluminescence spectra of pure ZnS nanoparticles showed an emission at 421 and 485nm which is blue emission which was originated from the defect sites of ZnS itself and also sulfur deficiency and when doped with Mn{sup 2+} an extra peak with high intensity was observed at 530nm which is nearly yellow-orange emission which isrelated to the presence of Mn in the host lattice.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

ZnO nanoparticles based fiber optic gas sensor

In this work, ZnO nanoparticles were synthesized by simple aqueous chemical route method. The synthesized ZnO nanoparticles were characterized by X-ray diffraction and scanning electron microscope. The sensitivity of the nanoparticles was studied for different gases like acetone, ammonia and ethanol in terms of variation in spectral light intensity. The XRD and SEM analysis confirms the formation of hexagonal wurtzite structure with the grain size of 11.2 nm. The small cladding region of the optical fiber was replaced with the synthesized nanoparticles. The light spectrum was recorded for different gas concentrations. The synthesized nanoparticles showed high sensitivity towards ammonia in low ppm level and acetone in high ppm level.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Simulation of an active cooling system for photovoltaic modules

Photovoltaic cells are devices that convert solar radiation directly into electricity. However, solar radiation increases the photovoltaic cells temperature [1] [2]. The temperature has an influence on the degradation of the cell efficiency and the lifetime of a PV cell. This work reports on a water cooling technique for photovoltaic panel, whereby the cooling system was placed at the front surface of the cells to dissipate excess heat away and to block unwanted radiation. By using water as a cooling medium for the photovoltaic solar cells, the overheating of closed panel is greatly reduced without prejudicing luminosity. The water also acts as a filter to remove a portion of solar spectrum in the infrared band but allows transmission of the visible spectrum most useful for the PV operation. To improve the cooling system efficiency and electrical efficiency, uniform flow rate among the cooling system is required to ensure uniform distribution of the operating temperature of the PV cells. The aims of this study are to develop a 3D thermal model to simulate the cooling and heat transfer in Photovoltaic panel and to recommend a cooling technique for the PV panel. The velocity, pressure and temperature distribution of the three-dimensional flow across the cooling block were determined using the commercial package, Fluent. The second objective of this work is to study the influence of the geometrical dimensions of the panel, water mass flow rate and water inlet temperature on the flow distribution and the solar panel temperature. The results obtained by the model are compared with experimental results from testing the prototype of the cooling device.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Lattice dynamics, electronic structure, and optical properties of LiBeSb: A hexagonal ABC-type hyperferroelectrics

The recently discovered hexagonal ABC-type hyperferroelectrics, in which the polarization persists in the presence of the depolarization filed, exhibit a variety of intriguing and potentially useful properties [Garrity et al., Phys. Rev. Lett. 112, 127601 (2014)]. For the existing prototype of LiBeSb, we present detailed first-principles calculations concerning the lattice dynamics, electronic structure, and optical properties. An unstable longitudinal optic mode in the high-symmetry structure and a large polarization of 0.5 C/m{sup 2} in the polar phase are reported, including the remarkable dependence of Born effective charges on structural distortion. Using the HSE06 hybrid functional, we predict that LiBeSb has a small band-gap of 1.5 eV and shows dominant asymmetric covalent bonding character. Importantly, we find that there are remarkable absorptions in the whole visible spectrum. These features, combined with the enhanced carrier mobility, make LiBeSb as well as the whole family of hexagonal ABC-type hyperferroelectrics as promising candidates for ferroelectric photovoltaic materials with large bulk photovoltaic effect in the visible spectrum.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Electronic and optical characterization of bulk single crystals of cubic boron nitride (cBN)

Cubic boron nitride (cBN) is a relatively less studied wide bandgap semiconductor despite its many promising mechanical, thermal, and electronic properties. We report on the electronic, structural, and optical characterization of commercial cBN crystal platelets. Temperature dependent transport measurements revealed the charge limited diode behavior of the cBN crystals. The equilibrium Fermi level was determined to be 0.47 eV below the conduction band, and the electron conduction was identified as n-type. Unirradiated dark and amber colored cBN crystals displayed broad photoluminescence emission peaks centered around different wavelengths. RC series zero phonon line defect emission peaks were observed at room temperature from the electron beam irradiated and oxygen ion implanted cBN crystals, making this material a promising candidate for high power microwave devices, next generation power electronics, and future quantum sensing applications.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Measurement and simulation of small cryogenic neon pellet Ne-I 640 nm photon efficiency during ablation in DIII-D plasma

Small (~1 mm) neon pellet fragments are fired into DIII-D H-mode plasmas, and resulting trajectory-averaged photon efficiencies (neutral neon ionization events for every photon emitted) of S/XB ≈ 85 are estimated for Ne-I 640 nm by dividing the estimated initial pellet fragment mass by the measured number of emitted Ne-I photons. The experiments are modeled by running the Lagrangian particle (LP) fluid/magneto-hydrodynamic pellet code to estimate axial ablation plume neon density profiles and temperature profiles at each pellet position. These solutions are then fed into the PrismSPECT collisional-radiative code, which calculates resulting neon charge states and photon emission rates, giving a profile-average of S/XB ≈ 109. The burnthrough plasma minor radius predicted by LP (ρ ≈ 0.63) is reasonably close to the experimental observation ρ ≈ 0.6. Furthermore, the modeling indicates that local S/XB is not constant along the pellet trajectory but tends to increase with increasing ablation rate. Non-equilibrium kinetics are predicted to be very important, while line trapping is predicted to be relatively unimportant (for Ne-I 640 nm S/XB).

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Threshold energies for filamentation and spectral characteristics of supercontinuum generation in THEOS-based nanocomposite organosilicon media

We have experimentally determined the threshold energy for filamentation in THEOS-based hybrid silicate nanocomposite materials containing polysaccharides and hyperbranched polyglycidols and the conversion efficiency from the 800-nm femtosecond Ti : sapphire laser output to a supercontinuum in the range 420 – 700 nm. The addition of sodium hyaluronate (polysaccharide) and low concentrations of Au nanoparticles or CdS quantum dots with an average diameter of 3 – 5 nm has been shown to considerably reduce the threshold energy for filamentation and improve the laser output to supercontinuum conversion efficiency. (extreme light fields and their applications)

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Generation of high-power femtosecond supercontinua in the near-IR spectral range using broadband parametric frequency conversion in LBO and DCDA crystals pumped at λ = 620 nm

The pump wavelength of parametric amplifiers based on CLBO, DCDA and LBO crystals and pumped by the second harmonic of a femtosecond Cr : forsterite laser (620 nm) is close to optimal for broadband amplification because of the proximity of group velocities of interacting pulses. Injection of a broadband continuum into the range of the signal-wave gain in LBO and DCDA parametric amplifiers, pumped at λ = 620 nm, leads to generation of broadband femtosecond pulses with a spectrum ranging from 1050 to 1600 nm and peak powers up to 20 MW. (nonlinear optical phenomena)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Experimental study of angular and frequency spectra of laser pulse diffraction on a planar periodic nanostructure of gold V antennas

Irradiation of a planar structure made of periodically spaced gold V antennas by a femtosecond pulsed laser has revealed several anomalously reflected and refracted waves, interpreted as diffraction maxima. Compression of the pulse spectrum in scattered light is observed. The degree of compression and wave polarisation are found to be determined by the scattering direction. (nanophotonics)

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Integrated high-order surface diffraction gratings for diode lasers

High-order surface diffraction gratings acting as a distributed Bragg reflector (DBR) in mesa stripe semiconductor lasers (λ = 1030 nm) have been studied theoretically and experimentally. Higher order interfering radiation modes (IRMs), which propagate off the plane of the waveguide, have been shown to have a crucial effect on the reflection and transmission spectra of the DBR. The decrease in the reflectivity of the DBR in response to the increase in the diffraction efficiency of these modes may reach 80% and more. According to theoretical analysis results, the intensity of the higher order IRMs is determined by the geometry of the DBR groove profile. Experimental data demonstrate that the noncavity modes are responsible for parasitic light leakage losses in the laser cavity. It has been shown that, in the case of nonoptimal geometry of the grating groove profile, the overall external differential quantum efficiency of the parasitic laser emission may exceed 45%, which is more than half of the laser output power. The optimal geometry of the DBR groove profile is trapezoidal, with the smallest possible lower base. Experimental evidence has been presented that this geometry considerably reduces the power of the higher order IRMs and minimises the parasitic light leakage loss. (lasers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

High-power optical parametric oscillator based on a high-pulse repetition rate, master Nd : KGW laser

An optical scheme of an optical parametric oscillator with a master laser based on an Nd : KGW active element excited by two orthogonally oriented diode side pump modules is proposed to form radiation pulses with energies above 30 mJ and a repetition rate of 1 – 20 Hz in the eye-safe spectral range of 1.5 – 1.6 μm. The two-module excitation of the active medium makes the distribution of the master laser radiation intensity in the output beam cross section more uniform and provides a reliable operation of the optical parametric oscillator. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Reflection of light beams from a chirped dielectric plane-layered structure

The reflection of light beams with various widths of the angular spectrum from a chirped plane-layered dielectric structure is numerically studied. For wide beams, the total lateral shift of the reflected beam depends on the position of the photonic barrier inside the structure and the value of the Goos – Hänchen shift. For narrow beams, the region of the interaction with the structure increases, the profile broadens and the reflected beam wavefront becomes phase modulated. It is shown that the light reflected from a quasi-periodic structure with negative spatial dispersion undergoes focusing. (light beams)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Experimental study of a joint-transform correlator

Results of an experimental study are presented for a working model of a joint-transform correlator with a liquid-crystal spatial light modulator at the input. Correlator operation with amplitude and phase modulation and various methods for joint power spectrum processing is compared to investigation results of the modelling partially performed earlier. A simple method is suggested for nonlinear processing of a joint spectrum, namely, limitation of its intensity by a photodetector. (optical processing of information)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Effect of light scattering on biological tissue thermometry from photoluminescence spectra of up-conversion nanoparticles

Photoluminescence spectra of the up-conversion nanoparticles NaYF{sub 4} : Y{sup 3+}, Er{sup 3+} arranged under a layer of an adipose tissue have been recorded in a wide temperature range. It is shown that if nanoparticle temperature is determined from the photoluminescence spectra, an error arises related to spectrum distortion due to light scattering in a sample. A correction algorithm for reducing this error is developed. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Multifrequency stimulated Raman scattering of light in a calcite single crystal

Using pulses of multifrequency stimulated Raman scattering (SRS) in calcite, nonlinear photoluminescence in a stilbene molecular crystal is excited. When multifrequency SRS is excited by the radiation of a Nd{sup 3+} : YAG laser with a wavelength of 1064 nm, eleven anti-Stokes components are observed in the visible spectrum with an average frequency shift of 1086 cm{sup −1} between them. Using the second harmonic of the Nd {sup 3+} : YAG laser radiation allowed three anti-Stokes and four Stokes components to be recorded. The large spectral range of the frequency comb facilitated effective reduction in the duration and increase in the intensity of the radiation pulse of multifrequency SRS. (nonlinear optical phenomena)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Study of eclipsing binary and multiple systems in ob associations. II. The cygnus ob region: V443 Cyg, V456 Cyg, and V2107 Cyg

Three presumably young eclipsing binary systems in the direction of the Cygnus OB1, OB3, and OB9 associations are studied. Component spectra are reconstructed and their orbits are determined using light curves and spectra disentangling techniques. V443 Cyg and V456 Cyg have circular orbits while the light curve of V2107 Cyg imposes a slightly eccentric orbit (e = 0.045 ± 0.03). V443 Cyg harbors F-type stars, not young early-A stars as previously suggested in the literature based solely on photometry. It appears to be situated in the foreground (distance 0.6 ± 0.2 kpc) of the young stellar populations in Cygnus. V456 Cyg, at a distance of 0.50 ± 0.03 kpc, consists of a slightly metal-weak A-type star and an early-F star. The age of both systems, on or very near to the main sequence, remains uncertain by an order of magnitude. V2107 Cyg is a more massive system (8.9 ± 2 and 4.5 ± 1.2 M {sub ☉}) at 1.5 ± 0.5 kpc and, also kinematically, a strong candidate-member of Cyg OB1. The more massive component is slightly evolved and appears to undergo non-radial βCep-type pulsations. The Doppler signal of the secondary is barely detectable. A more extensive, asteroseismological study is necessary to fix masses more precisely. Nevertheless, the position of the primary in the H-R diagram confines the age reasonably well to 20 ± 5 Myr, indicating that for Cyg OB1 has a similar extent of star formation history as that established for Cyg OB2.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Absolute properties of the eclipsing binary star IM Persei

IM Per is a detached A7 eccentric eclipsing binary star. We have obtained extensive measurements of the light curve (28,225 differential magnitude observations) and radial velocity curve (81 spectroscopic observations) which allow us to fit orbits and determine the absolute properties of the components very accurately: masses of 1.7831 ± 0.0094 and 1.7741 ± 0.0097 solar masses, and radii of 2.409 ± 0.018 and 2.366 ± 0.017 solar radii. The orbital period is 2.25422694(15) days and the eccentricity is 0.0473(26). A faint third component was detected in the analysis of the light curves, and also directly observed in the spectra. The observed rate of apsidal motion is consistent with theory (U = 151.4 ± 8.4 year). We determine a distance to the system of 566 ± 46 pc.

79 ASTRONOMY AND ASTROPHYSICS↗