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Results for “RAMAN EFFECT”

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 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
NASA NTRS2018

Fiber-Based Laser MOPA Transmitter Packaging for Space Environment

NASA’s Goddard Space Flight Center has been developing lidar to remotely measure CO2 and CH4 in the Earth’s atmosphere. The ultimate goal is to make space-based satellite measurements with global coverage. We are working on maturing the technology readiness of a fiber-based, 1.57-micron wavelength laser transmitter designed for use in atmospheric CO2 remote-sensing. To this end, we are building a ruggedized prototype to demonstrate the required power and performance and survive the required environment. We are building a fiber-based master oscillator power amplifier (MOPA) laser transmitter architecture. The laser is a wavelength-locked, single frequency, externally modulated DBR operating at 1.57-micron followed by erbium-doped fiber amplifiers. The last amplifier stage is a polarization-maintaining, very-large-mode-area fiber with ~1000 μm2 effective area pumped by a Raman fiber laser. The optical output is single-frequency, one microsecond pulses with >450 μJ pulse energy, 7.5 KHz repetition rate, single spatial mode, and > 20 dB polarization extinction.

Lasers and Masers↗
DOE OSTI2017

Irradiation Accelerated Corrosion of Stainless Steel and Ferritic-Martensitic Steel in Simulated Primary Water

Austenitic stainless steel, and ferritic-martensitic steel were irradiated with a proton beam while simultaneously exposed to simulated PWR primary water. Samples were exposed for 4-72 hr in 320°C water with 3 wppm hydrogen while simultaneously irradiated at surface dose rates from 400-4000 kGy/s (4x10-7 to 7x10-6 dpa/s). After exposure, samples were characterized with TEM, EDS, and Raman spectroscopy to determine the effects of radiation on the growth and stability of the oxide films. Samples which were irradiated during exposure had thinner inner oxides compared to unirradiated samples. Irradiated samples also had hematite on their surfaces, while unirradiated samples did not, indicating an increase in corrosion potential due to irradiation. Sample regions which were not irradiated but were exposed to the flow of irradiated water were similar to directly irradiated regions, suggesting that water radiolysis is the mechanism primarily responsible for the observed effects.

Stainless Steel, ferritic-martensitic steel, radia↗
DOE OSTI2021

Free-space confocal magneto-optical spectroscopies at milliKelvin temperatures

We describe the operation of a free-space confocal optical microscope operated in a dilution refrigerator. The microscope is installed on a cold insertable probe to enable fast sample exchange while the refrigerator is held at low temperatures. A vector magnet provides a 6 T field normal to the sample and 1 T fields at arbitrary angles. A variety of optical microscopies and spectroscopies, including photoluminescence, Raman, magneto-optical Kerr effect, and spin relaxometry measurements are described, and some of the challenges associated with performing these measurements at milliKelvin temperatures are explored.

Lawrie, Benjamin↗
DOE OSTI2015

Transfer-free graphene synthesis on sapphire by catalyst metal agglomeration technique and demonstration of top-gate field-effect transistors

Transfer-free graphene synthesis was performed on sapphire substrates by using the catalyst metal agglomeration technique, and the graphene film quality was compared to that synthesized on sputtered SiO{sub 2}/Si substrates. Raman scattering measurements indicated that the graphene film on sapphire has better structural qualities than that on sputtered SiO{sub 2}/Si substrates. The cross-sectional transmission microscopic study also revealed that the film flatness was drastically improved by using sapphire substrates instead of sputtered SiO{sub 2}/Si substrates. These quality improvements seemed to be due the chemical and thermal stabilities of sapphire. Top-gate field-effect transistors were fabricated using the graphene films on sapphire, and it was confirmed that their drain current can be modulated with applied gate voltages. The maximum field-effect mobilities were estimated to be 720 cm{sup 2}/V s for electrons and 880 cm{sup 2}/V s for holes, respectively.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Phase sensitive Raman process with correlated seeds

A phase sensitive Raman scattering was experimentally demonstrated by injecting a Stokes light seed into an atomic ensemble, whose internal state is set in such a way that it is coherent with the input Stokes seed. Such phase sensitive characteristic is a result of interference effect due to the phase correlation between the injected Stokes light field and the internal state of the atomic ensemble in the Raman process. Furthermore, the constructive interference leads to a Raman efficiency larger than other kinds of Raman processes such as stimulated Raman process with Stokes seed injection alone or uncorrelated light-atom seeding. It may find applications in precision spectroscopy, quantum optics, and precise measurement.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Carbon-rich hexagonal (BN)C alloys

Thin films of hexagonal boron nitride carbon, h-(BN){sub 1−x}(C{sub 2}){sub x}, alloys in the C-rich side have been synthesized by metal-organic chemical vapor deposition (MOCVD) on c-plane sapphire substrates. X-ray diffraction measurements confirmed single hexagonal phase of h-(BN){sub 1−x}(C{sub 2}){sub x} epilayers. Electrical transport and Raman spectroscopy measurements results revealed evidences that homogenous h-(BN){sub 1−x}(C{sub 2}){sub x} alloys with x ≥ 95% can be synthesized by MOCVD at a growth temperature of 1300 °C. The variable temperature Hall-effect measurements suggested that a bandgap opening of about 93 meV with respect to graphite has been obtained for h-(BN){sub 1−x}(C{sub 2}){sub x} with x = 0.95, which is consistent with the expected value deduced from the alloy dependence of the energy gap of homogenous h-(BN){sub 1−x}(C{sub 2}){sub x} alloys. Atomic composition results obtained from x-ray photoelectron spectroscopy measurements revealed that the carrier type in C-rich h-(BN){sub 1−x}(C{sub 2}){sub x} alloys is controlled by the stoichiometry ratio between the B and N via changing the V/III ratio during the growth. The demonstration of bandgap opening and conductivity control in C-rich h-(BN){sub 1−x}(C{sub 2}){sub x} alloys provide feasibilities for realizing technologically significant devices including infrared (IR) emitters and detectors active from near to far IR and multi-spectral IR emitters and detectors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Chitosan/Polyaniline Conductive Blends for Developing Packaging: Electrical, Morphological, Structural and Thermal Properties

The present study aim to evaluate the development of electrical conducting blends made from the biodegradable polymer, chitosan (Cs), and polyaniline (PANI) doped with dodecylbenzene sulfonic acid dissolved in acid solution chitosan, to enable development of conductive and smart packages that help to monitor exposure conditions of food aimed to reduce food waste. Concentration of Cs is fixed (2%), and PANI (80, 100 mg mL{sup −1}) and glutaraldehyde (Glut) (0.625 × 10{sup −3} μL) concentrations are alter. Morphological (SEM), structural (FTIR, RAMAN), thermal (TGA) and electrical (Hall effect) properties are evaluate. Blends were predominantly negative carriers, with conductivity in order of 10{sup −1} S cm{sup −1}. Best formulations are those make without of Glut. Analyses show an interaction between components. FTIR show bands characteristic of benzene and quinoid rings of PANI, and RAMAN exhibit a band related to PANI’s protonation. TGA show maintenance of maximum degradation temperature of PANI. This results evidence maintenance of PANI’s conducting structures even after blends synthesis.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Onset of stimulated Raman scattering of a laser in a plasma in the presence of hot drifting electrons

Stimulated Raman scattering of a laser in plasmas with energetic drifting electrons was investigated by analyzing the growth of interacting waves during the Raman scattering process. The Langmuir wave and scattered electromagnetic sideband wave grow initially and are dampened after attaining a maximum level that indicates a periodic exchange of energy between the pump wave and the daughter waves. The presence of energetic drifting electrons in the laser-produced plasma influences the stimulated Raman scattering process. The plasma wave generated by Raman scattering may be influenced by the energetic electrons, which enhance the growth rate of the instability. Our results show that the presence of energetic (hot) drifting electrons in a plasma has an important effect on the evolution of the interacting waves. This phenomenon is modeled via two-dimensional particle-in-cell simulations of the propagation and interaction of the laser under Raman instability.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Probing Biomolecular Interactions with Gold Nanoparticle-Decorated Single-Walled Carbon Nanotubes

Hybrid nanomaterials comprising metal–graphitic interfaces are uniquely suitable to probe molecular interactions and the associated phenomena such as charge transfer and adsorbate spillover effects. In this paper, we study the modulation of the electronic and chemical properties of gold nanoparticle-decorated single-walled carbon nanotubes (SWCNT) using Raman spectroscopy and measurements of field-effect transistor (FET) characteristics. SWCNT are extremely sensitive to changes in the local electronic environment and therefore gold-analyte interactions may be probed both through changes in FET characteristics (as an electrical transducer) and in surface-enhanced Raman scattering (as a chromophore). We study these changes both experimentally and theoretically in order to elucidate the electronic structure of complex nanocomposites, and the information gathered from these experiments is applied to the study of biomolecular interactions with gold nanoparticle-decorated SWCNT. Lastly, this study, in addition to providing deeper understanding of metal–graphitic interfaces, will offer a combined approach to SWCNT biosensing methodology based on the dual monitoring of the FET–Raman characteristics, which we demonstrate through detection of glutathione.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Network upgrade exploiting multi band: S- or E-band?

Nowadays, the fiber spectrum is only partially exploited, i.e., mainly in the C-band and more recently in the C + L-band, where the fiber attenuation profile experiences the minimum. Thus, fiber communications technology—amplifiers, switching, transceivers, etc.—and networking solutions are mature for those spectrum bands. However, the continuous increase in traffic means that capacity saturation of the current infrastructure is looming. Taking advantage of the unused portions of the spectrum (e.g., the S- and E-bands) may be an efficient solution to accommodate an increase in traffic without installing new fibers. Research is thus investigating multi-band transmission and networking to evaluate and enable such network upgrades. Some issues need to be solved or taken into account, from the enabling technology (e.g., amplifiers in the S- or E-band are still under development) to physical layer effects previously neglected, such as stimulated Raman scattering (SRS). SRS affects wideband transmission, potentially degrading active channels. The contribution of this paper is the investigation of network upgrades for C + L-band systems. In particular, upgrades exploiting the E- and S-bands are compared taking into account each band capacity and the effects of SRS on both new and already deployed channels (in both the C- and L-bands). A detailed analysis of the physical layer is provided also in the presence of guard bands between previously exploited bands and the bands used for upgrade. By leveraging the physical layer assessment, a networking analysis is carried out to evaluate the supported traffic increase and also the signal quality degradation due to SRS on active channels. Overall, the results suggest that upgrades to the E- and S-bands support a comparable increase in traffic. However, the exploitation of the E-band with 14 THz of guard band between the C- and E-bands may avoid detrimental effects to already active channels in the C + L-band, suggesting this upgrade strategy can be the most effective of the two.

47 OTHER INSTRUMENTATION↗
DOE OSTI2018

An effective strategy to enhancing tolerance to contaminants poisoning of solid oxide fuel cell cathodes

Commercialization of solid oxide fuel cells (SOFCs) is impeded by severe cathode degradation from the poisoning effect of contaminants commonly encountered in air (such as H 2 O and CO 2 ) and from other cell components (e.g., Cr species from chromium-containing interconnector). Here we report our findings in unraveling the mechanism of Cr poisoning of La .6 Sr .4 Co .2 Fe .8 O 3 (LSCF) cathodes using our unique in situ/operando surface enhanced Raman spectroscopy. Further, we present an effective strategy to enhancing the tolerance to contaminants poisoning of LSCF cathode through infiltration of a hybrid catalyst coating, which is composed of a conformal film of perovskite PrNi .5 Mn .5 O 3 (PNM) and exsoluted PrO x nano-particles. The coating is catalytically active to oxygen reduction reaction but inert to contaminant poisoning. When subjected to an accelerated Cr-poisoning test, the cells with a hybrid catalyst-coated LSCF cathode show excellent peak power density (P max of 0.71 Wcm -2 ) and significantly enhanced durability (degradation rate of 0.0434% h -1 at 0.7 V), much better than those of cells with a bare LSCF cathode (P max of ~0.46 Wcm -2 and degradation rate of 0.4% h -1 at 0.7 V). The results suggest that surface modification of electrodes with a coating of rationally designed catalysts is a cost-effective approach to dramatically reducing electrode degradation caused by contaminations.

25 ENERGY STORAGE↗
NASA NTRS1992

Observations of stimulated Raman scattering and laser-induced breakdown in millimeter-sized droplets

We report the first observations, to our knowledge, of nonlinear optical effects in large (millimeter-sized) droplets. Stimulated Raman scattering (SRS) and laser-induced breakdown (LIB) are simultaneously observed in acoustically levitated millimeter-sized glycerol droplets irradiated by either a frequency-doubled (532-nm) or a frequency-tripled (355-nm) Nd:YAG laser. The two processes, which occur above a nearby coincident irradiation threshold, are conjectured to arise from a common initiation mechanism: self-focusing. LIB generates vapor bubbles within the droplet, resulting in the quenching of SRS emission.

Biswas, A.↗
DOE OSTI2019

Multifrequency Stimulated Raman Scattering on Rotational Transitions of Molecules

The theory of multifrequency stimulated Raman scattering (SRS) of light on rotational transitions of molecules, which are simulated by a three-level quantum system, is developed. It is shown that the application of bichromatic pumping increases the scattered radiation spectrum width. The exact algebraic solution for the wave amplitudes is obtained in the simplest version of synchronous SRS on transitions with a negligibly low eigenfrequency. It is found that an increase in the ratio of the Raman transition frequency to the pump radiation frequency leads to predominance of the anti-Stokes scattering branch. The effect of wave asynchronism emerging due to linear and nonlinear dispersion of the medium as well as the phase difference of the pump waves on SRS is considered. All types of asynchronism narrow generated frequency spectrum and suppress the anti-Stokes scattering branch. Nonlinear dispersion ensures positive values of wave amplitudes due to phase jumps by π during the propagation of waves in a medium.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2015

Electronic states and phonon properties of Ge{sub x}Si{sub 1−x} nanostructures

Ge{sub x}Si{sub 1−x} nanostructures that can be manipulated through size reduction, geometry variation, and alloying, are considered as one of the key developments for next generation technologies, due to their easy processing, unique properties, and compatibility with the existent silicon-based microelectronic industry. In this review, we have thoroughly discussed the major advances in electronic structures and phonon properties of Ge{sub x}Si{sub 1−x} nanocrystals (NCs). Experimental and theoretical characterization related to several main factors, for example, size, composition, strain, temperature, and interface and surface were presented with special emphasis in low-frequency Raman scattering. Current difficulties in explaining the Raman spectra are the assignment of the low-frequency modes because of the complexity of the environment around the NCs, thus different theoretical models are introduced in detail to deal with different properties of Ge{sub x}Si{sub 1−x} alloy NCs including Lamb’s theory, complex-frequency (CF) model, core–shell matrix (CMS) model and spatial coherence effect model. - Highlights: • Major advances in electronic structures and phonon properties of Ge{sub x}Si{sub 1−x} nanocrystals are discussed thoroughly. • Experimental and theoretical characterization related to size, composition, strain, temperature, and interface/surface are elucidated. • Low-frequency Raman spectra are specially described based on spatial coherence effect model.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Geometric phase and entanglement of Raman photon pairs in the presence of photonic band gap

Robustness of the geometric phase (GP) with respect to different noise effects is a basic condition for an effective quantum computation. Here, we propose a useful quantum system with real physical parameters by studying the GP of a pair of Stokes and anti-Stokes photons, involving Raman emission processes with and without photonic band gap (PBG) effect. We show that the properties of GP are very sensitive to the change of the Rabi frequency and time, exhibiting collapse phenomenon as the time becomes significantly large. The system allows us to obtain a state which remains with zero GP for longer times. This result plays a significant role to enhance the stabilization and control of the system dynamics. Finally, we investigate the nonlocal correlation (entanglement) between the pair photons by taking into account the effect of different parameters. An interesting correlation between the GP and entanglement is observed showing that the PBG stabilizes the fluctuations in the system and makes the entanglement more robust against the change of time and frequency.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Single laser pulse compression via strongly coupled stimulated Brillouin scattering in plasma

Laser amplification in plasma, including stimulated Raman scattering amplification and strongly coupled stimulated Brillouin scattering (sc-SBS) amplification, is very promising to generate ultrahigh-power and ultrashort laser pulses. But both are quite complex in experiments: at least three different laser pulses must be prepared; temporal delay and spatial overlap of these three pulses are difficult. We propose a single pulse compression scheme based on sc-SBS in plasma. Only one moderately long laser is applied, the front part of which ionizes the gas to produced plasma, and gets reflected by a plasma mirror at the end of the gas channel. The reflected front quickly depletes the remaining part of the laser by sc-SBS in the self-similar regime. The output laser is much stronger and shorter. This scheme is at first considered theoretically, then validated by using 1D PIC simulations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗