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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 73 records · Page 4

Preparation and Studies of Thin Films of Cu-doped GdSr{sub 2}RuCu{sub 2}O{sub 8}

Preparation of superconducting thin films of the Cu-doped Ruthenocuprate superconductor GdSr{sub 2}Ru{sub 0.9}Cu{sub 2.1}O{sub 8} has been attempted by pulsed laser deposition method. Thin films were deposited on different substrates employing different laser ablation parameters with the idea of obtaining good-quality films which exhibit superconductivity. The crystal structure and morphology of the thin films were characterized by X-ray diffraction and scanning electron microscopy measurements and optical characteristics by Raman scattering measurements. High-temperature ex situ oxygen annealing led to the formation of homogeneous films with the occurrence of an onset of superconductivity, traced by electrical resistivity measurements. Increasing the annealing time has led to a systematic improvement in the sample quality and the physical properties. However, prolonged high-temperature annealing seems to cause deterioration in properties as seen from electrical resistivity and Raman scattering measurements. The studies reveal the importance of an optimal high-temperature oxygen annealing procedure to induce superconductivity in thin films of this Ruthenocuprate system.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

On the efficiency of different numerical methods for the calculation of intrapulse Raman scattering of optical solitons

In this paper we compare the performance of different numerical methods for the calculation of the asymptotic evolution of soliton self-frequency shift in the presence of intrapulse Raman scattering (IRS) in optical fibers. First we have calculated the order of global accuracy for the fundamental soliton and the second-order bound state of the unperturbed nonlinear Schrödinger equation for the following numerical methods: the simple split step (SS) method, the full SS method, the reduced SS method, the reduced SS method with fourth order Runge–Kutta (RK4), the Blow–Wood method, the fourth order Runge–Kutta in the interaction picture (RK4IP) method and the Agrawal SS method with one and two iterations. We have shown that the asymptotic evolution of soliton self-frequency shift in the presence of IRS in optical fiber can be best described by the Agrawal SS method (compared to the Blow–Wood method and the RK4IP method). The obtained numerical results for the soliton position and frequency are in agreement with the predictions for these parameters according to the perturbation theory. We have shown that in the presence of IRS the fundamental soliton quickly develops an oscillating tail on its left. The generated tail hardly influences the soliton propagation at large distances. At large distances the form of the soliton gradually becomes asymmetric. The increase of the frequency resolution leads to a notable increase of the maximum propagation distance of the numerical soliton under the influence of IRS.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Estimation of Crystal Lattice Deformations with Depth of Proton-Exchanged Optical Waveguides on Lithium Niobate Single Crystal Substrates

A method for determining the crystal phase and estimating the crystal lattice deformations in H{sub x}Li{sub 1-x}NbO{sub 3} proton-exchanged optical waveguides from an analysis of the Raman light scattering spectra measured with high spatial resolution (the so-called method of micro-RS spectroscopy) is suggested.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

The location of Sb luminescence centers in Ca10(PO4)6F2 phosphors

Highlights: • Sb is on Ca2 sites (N center) in commercial phosphors, literature conflict ended. • N centers are covalently bonded SbO pairs have IR absorption band at 685 cm{sup −1}. • Incorporation of Na converts N to HE centers by removal of O on F sites. • Proportions of N and HE precisely controlled by Na/Sb molar ratio. • Luminescence of N and HE centers is very different, both are described in detail. - Abstract: The luminescence centers in antimony doped fluorapatite phosphors were characterized by optical emission spectroscopy, IR and FTIR absorption, and Raman scattering. The luminescence centers in commercial phosphors consist of covalently bound SbO pairs (N center). The vibrational spectrum of analogous BiO pairs was studied for the first time in FAP. New methods of preparation yielded material with a record high level of SbO doping. There is a second well established (HE) center which consists of Sb on Ca2 sites and Na at nearby Ca1 or Ca2 sites. The properties of the N and HE centers differ greatly and are described in detail. We showed for the first time that HE centers like N centers can efficiently sensitize the fluorescence of manganese in FAP.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Chemical Durability and Dissolution Kinetics of Iodoapatite in Aqueous Solutions

Understanding the long-term release of radionuclides from nuclear waste to the environment is critical for public acceptance and sustainability of nuclear energy. Iodoapatite, a synthetic material similar to mineral vanadinite proposed for radioactive iodine-129 immobilization, is employed in this study as a model system for iodine waste forms and ceramic waste forms in general to understand its long-term chemical durability. Semidynamic leaching experiments were performed in cap-sealed Teflon vessels to evaluate the chemical durability at temperatures from 20 to 90 degrees C and pH values from 4 to 9 using deionized water and pH buffer solutions. The leachates were analyzed using inductively coupled plasma-mass spectrometry. The leached surfaces were examined by X-ray diffraction, scanning electron microscopy, and Raman spectroscopy. Effects of test variables including surface-to-volume ratio, leachant replacement interval, and environmental variables including temperature and pH on the dissolution rate were systematically investigated. The activation energy of the dissolution was 16.9 ± 1.5 kJ/mol for the matrix elements and 34.4 ± 3.9 kJ/mol for the diffusive iodine release. The order of the pH effect on the dissolution rate as a power law exponent was 0.87 ± 0.08. The effect of the surface-to-volume ratio and replacement interval was approximated by a single exponential function rise to maximum. Fully parametrized models were then combined to predict iodine release rate under various conditions. The result suggests that the long-term iodine release is controlled by iodide diffusion when the matrix dissolution rate is very low in near neutral pH solutions and by matrix dissolution when the dissolution rate is high at low pH. The present study demonstrates a mechanistic approach to parametrize models that can be used to evaluate the performance of nuclear waste forms under various disposal environments.

36 MATERIALS SCIENCE↗

Experimental investigation of nonlinear operation mode of a DP-QPSK 100G link with co-propagating-pump Raman amplification

The nonlinear interference noise in a coherent single-span fibre-optic communication link (FOCL) with co-propagating Raman amplification is investigated at different levels of input Raman pump and channel powers and dispersion. A simple phenomenological expression for calculating the nonlinear noise power at the output of a single-channel FOCL is presented. The merit of using a distributed Raman amplifier with co-propagating pump up to 1 W in a single-span single-channel FOCL is experimentally investigated. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Parametric stimulated Raman scattering in barium nitrate crystals

The spectra of multifrequency parametric stimulated Raman scattering in a barium nitrate single crystal is investigated. When this single crystal is excited by ultrashort (80 ps) YAG : Nd{sup 3+} laser pulses with a wavelength of 1064 nm, a frequency comb of eight anti-Stokes components is observed in the visible spectral range. The Raman satellites are due to the totally symmetric vibrational modes of barium nitrate single crystal. The frequencies of the corresponding Raman Stokes components in the IR range (from 1193 to 9662 nm) are calculated. The results of the study open the way to form an array of laser frequencies from the IR to green spectral range with a period of 1047 cm{sup –1}. (nonlinear optical phenomena)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Enhancement of local electromagnetic fields by periodic optical resonators

The periodically profiled metasurfaces of silicon and of the same surfaces coated with a thin layer of silver are experimentally investigated to improve the signal-to-noise ratio in the observation of Raman light scattering from molecular compounds. The noise in this case is the unavoidable background molecular luminescence. Our experimental and computer simulation data demonstrate an anomalous optical response due to the excitation of metal-dielectric surface resonances. An enhanced Raman scattering signal is observed from 5,5′-dithiobis(2-nitrobenzoic) acid (DTNB) organic molecules deposited on the metasurface. The proposed metasurface provides a significant enhancement of the RS signal in comparison with the luminescence signal and is an efficient substrate for realising giant Raman scattering of light. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Monoclinic LaBWO{sub 6}: A new SRS-active crystal

We have synthesised a new SRS-active LaBWO{sub 6} tungstate crystal with a high steady-state Raman gain (less than 2.8 cm GW{sup −1}) and ability to generate a multicomponent Stokes and anti-Stokes comb in the visible and near-IR spectral regions, with a length of ∼13010 cm{sup −1}. The newly found photon – phonon nonlinear χ{sup (3)} processes in known SRS- and laser-active tungstate crystals are briefly described in tables. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

SRS converter – compressor of femtosecond ytterbium laser pulses

Stimulated Raman scattering (SRS) conversion of femtosecond pulses of an ytterbium laser at a wavelength of 1.03 μm is performed in compressed hydrogen under conditions of nonlinear phase modulation. Temporal compression of frequency-chirped Stokes pulses is carried out, as a result of which 400-fs laser pulses are converted into 27-fs Stokes pulses with a wavelength of 1.8 μm. An average Stokes power of 0.6 W is implemented at an average laser power of 6.3 W and a pulse repetition rate of 20 kHz. (nonlinear optical phenomena)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Temperature estimation in a spatially inhomogeneous flame by diode laser absorption spectroscopy

A two-temperature (2T) model is proposed for estimating the temperature of a spatially inhomogeneous hot zone using single-beam diode laser absorption spectrometry. The proposed algorithm is based on fitting experimental absorption spectra by a linear combination of two database-simulated single-temperature spectra with different temperatures. The model efficiency is experimentally demonstrated when determining the temperature in different flame zones of a Wolfgard – Parker slot burner. The proposed 2T algorithm is used to find the maximum and minimum temperatures in different flame sections, which are compared with local temperatures in the same flame zones measured by the method of coherent anti-Stokes Raman scattering (CARS). It is shown that the maximum temperatures determined by the proposed 2T algorithm are in good agreement with CARS data in flame zones where high-temperature regions prevail. A good agreement between the minimum temperatures obtained by these two methods is also observed for predominantly cold zones. (paper)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

Distributed fibre-optic temperature sensor for cryogenic applications based on detection of boson components of Raman light scattering

The possibility of designing a distributed fibre-optic sensor, allowing one to measure cryogenic temperatures (to liquid nitrogen boiling point), is experimentally demonstrated. The principle of operation of the sensor is based on measuring the intensity of boson peaks of Raman scattering in a fibre material, which are spaced by 1 to 3 THz from the probe frequency. The measurements are performed using a single-mode telecommunication fibre with a 15-μm-thick polyimide coating. The probe wavelength is 1.55 μm, the sensor spatial resolution is 4 m, and the averaging time is 60 s. Experiments are carried out in the temperature range of 75.6 – 79.6 K, with a temperature resolution of 0.5 K. (paper)

36 MATERIALS SCIENCE↗

Decreasing the amplitude of macroscopic quantum fluctuations in the case of transient SRS

It is shown experimentally that, under the conditions of transient stimulated Raman scattering, pumping by two successive orthogonally polarised laser pulses makes it possible to reduce the amplitude of macroscopic quantum energy fluctuations of a Stokes pulse by a factor of 4 in comparison with single-shot pumping. An energy dispersion of 0.9 % for the first Stokes component is obtained in hydrogen at a relative energy dispersion of ytterbium laser pulses of 0.4 %. (nonlinear optical phenomena)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Spectrally selective fundamental core mode suppression in optical fibre containing absorbing rods

The feasibility of making a wavelength-selective fibre filter using fibre with absorbing rods in its silica cladding has been demonstrated theoretically for the first time. The technique described in this paper is of great practical interest for designing fibre lasers and amplifiers emitting at wavelengths where lasing is impeded by the presence of more energetically favourable radiative transitions in the active medium. In addition, the approach proposed here can be used for stimulated Raman scattering suppression. The unique feature of the fundamental core mode suppression mechanism examined is that there is a (bending) controlled spectral width of a region where excess losses are produced. (selection of papers presented at the international workshop on fibre lasers (20 – 24 September 2020, Novosibirsk))

36 MATERIALS SCIENCE↗

Observation of well-defined Kohn-anomaly in high-quality graphene devices at room temperature

Abstract Due to its ultra-thin nature, the study of graphene quantum optoelectronics, like gate-dependent graphene Raman properties, is obscured by interactions with substrates and surroundings. For instance, the use of doped silicon with a capping thermal oxide layer limited the observation to low temperatures of a well-defined Kohn-anomaly behavior, related to the breakdown of the adiabatic Born–Oppenheimer approximation. Here, we design an optoelectronic device consisting of single-layer graphene electrically contacted with thin graphite leads, seated on an atomically flat hexagonal boron nitride substrate and gated with an ultra-thin gold layer. We show that this device is optically transparent, has no background optical peaks and photoluminescence from the device components, and no generation of laser-induced electrostatic doping (photodoping). This allows for room-temperature gate-dependent Raman spectroscopy effects that have only been observed at cryogenic temperatures so far, above all the Kohn-anomaly phonon energy normalization. The new device architecture, by decoupling graphene optoelectronic properties from the substrate effects, allows for observing quantum phenomena at room temperature.

Materials Science↗

Revealing excitonic processes and chemical bonding in Mo S 2 by x-ray spectroscopy

Electron core-hole processes at absorption edges sport several signatures, primarily in the form of bound states and/or excitonic enhancement. Here, through analysis of the resonant-Raman Auger effect for the two-dimensional transition-metal dichalcogenide MoS 2 , we demonstrate that these effects have significant manifestations at the S K edge. We characterize two asymmetric excitonically enhanced edges: one at the fundamental band edge and one several electron volts above it following a second band gap that lies entirely within the unoccupied states, with the latter revealing an anomalous postcollision interaction effect. In conclusion, our interpretation is supported by comparison of both the photoemission valence-band spectrum and the S K-edge x-ray-absorption spectrum with electronic structure calculations and an ab initio solution of the Bethe-Salpeter equation that accurately accounts for the electron-core-hole interaction.

47 OTHER INSTRUMENTATION↗

Optical Properties of Copper-Doped Lithium Niobate Crystals

We have studied the optical properties of copper-doped lithium niobate crystals using semiconductor light-emitting diodes and lasers emitting in the visible and ultraviolet spectral regions as excitation sources. The results demonstrate that, at an excitation frequency approaching the frequency of electronic absorption in copper ions, there is discrete resonance Raman scattering in the form of a frequency comb. The observed Raman satellites of discrete light scattering are due to polar longitudinal A{sub 1} optical modes of the lithium niobate single crystal. Under excitation by a light-emitting diode with a wavelength of 520 nm, we observe a sharp increase in discrete light scattering intensity in comparison with the photoluminescence excited by shorter wavelength excitation sources.

36 MATERIALS SCIENCE↗