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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

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↗
DOE OSTI2019

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↗
DOE OSTI2019

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↗
DOE OSTI2020

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 ↗
DOE OSTI2020

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↗
DOE OSTI2020

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↗
DOE OSTI2020

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↗
DOE OSTI2013

ASYMMETRIC ABSORPTION PROFILES OF Ly{alpha} AND Ly{beta} IN DAMPED Ly{alpha} SYSTEMS

Damped Ly{alpha} systems observed in the quasar spectra are characterized by a high neutral hydrogen column density, N{sub HI} > 2 x 10{sup 20} cm{sup -2}. The absorption wing profiles are often fitted using the Voigt function due to the fact that the scattering cross section near the resonant line center is approximately described by the Lorentzian function. Since a hydrogen atom has infinitely many p states that participate in the electric dipole interaction, the cross section starts to deviate from the Lorentzian in an asymmetric way in the line wing regions. We investigate this asymmetry in the absorption line profiles around Ly{alpha} and Ly{beta} as a function of the neutral hydrogen column density N{sub HI}. In terms of {Delta}{lambda} {identical_to} {lambda} - {lambda}{sub {alpha}}, we expand the Kramers-Heisenberg formula around Ly{alpha} to find {sigma}({lambda}) {approx_equal} (0.5f{sub 12}){sup 2}{sigma}{sub T}({Delta}{lambda}/{lambda}{sub {alpha}}){sup -2}[1 + 3.792({Delta}{lambda}/{lambda}{sub {alpha}})], where f{sub 12} and {sigma}{sub T} are the oscillator strength of Ly{alpha} and the Thomson scattering cross section, respectively. In terms of {Delta}{lambda}{sub 2} {identical_to} {lambda} - {lambda}{sub {beta}} in the vicinity of Ly{beta}, the total scattering cross section, given as the sum of cross sections for Rayleigh and Raman scattering, is shown to be {sigma}({lambda}) {approx_equal} {sigma}{sub T}(0.5f{sub 13}){sup 2}(1 + R{sub 0})({Delta}{lambda}{sub 2}/{lambda}{sub {beta}}){sup -2}[1 - 24.68({Delta}{lambda}{sub 2}/{lambda}{sub {beta}})] with f{sub 13} and the factor R{sub 0} = 0.1342 being the oscillator strength for Ly{beta} and the ratio of the Raman cross section to Rayleigh cross section, respectively. A redward asymmetry develops around Ly{alpha}, whereas a blue asymmetry is obtained for Ly{beta}. The absorption center shifts are found to be almost proportional to the neutral hydrogen column density.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Mass-loss rate by the MIRA in the symbiotic binary V1016 Cygni from Raman scattering

The mass-loss rate from Mira variables represents a key parameter in our understanding of their evolutionary tracks. We introduce a method for determining the mass-loss rate from the Mira component in D-type symbiotic binaries via the Raman scattering of atomic hydrogen in the wind from the giant. Using our method, we investigated Raman He ii λ1025→λ6545 conversion in the spectrum of the symbiotic Mira V1016 Cyg. We determined its efficiency, η = 0.102, 0.148, and the corresponding mass-loss rate, M-dot =2.0{sub −0.2}{sup +0.1}×10{sup −6}, 2.7{sub −0.1}{sup +0.2}×10{sup −6} M{sub ⊙} yr{sup −1}, using our spectra from 2006 April and 2007 July, respectively. Our values of M-dot that we derived from Raman scattering are comparable with those obtained independently by other methods. Applying the method to other Mira–white dwarf binary systems can provide a necessary constraint in the calculation of asymptotic giant branch (AGB) evolution.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Formation of Raman scattering wings around Hα, Hβ, AND PAα in active galactic nuclei

Powered by a supermassive black hole with an accretion disk, the spectra of active galactic nuclei (AGNs) are characterized by prominent emission lines including Balmer lines. The unification schemes of AGNs require the existence of a thick molecular torus that may hide the broad emission line region from the view of observers near the equatorial direction. In this configuration, one may expect that the far-UV radiation from the central engine can be Raman scattered by neutral hydrogen to reappear around Balmer and Paschen emission lines, which can be identified with broad wings. We produce Hα, Hβ, and Paα wings using a Monte Carlo technique to investigate their properties. The neutral scattering region is assumed to be a cylindrical torus specified by the inner and outer radii and the height. While the covering factor of the scattering region affects the overall strengths of the wings, the wing widths are primarily dependent on the neutral hydrogen column density N{sub H I} being roughly proportional to N{sub H I}{sup 1/2}. In particular, with N{sub H I}=10{sup 23} cm{sup −2} the Hα wings typically show a width ∼2×10{sup 4} km s{sup −1}. We also find that Hα and Paα wing profiles are asymmetric with the red part stronger than the blue part and an opposite behavior is seen for Hβ wings.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

AN EXTREME HIGH-VELOCITY BIPOLAR OUTFLOW IN THE PRE-PLANETARY NEBULA IRAS 08005-2356

We report interferometric mapping of the bipolar pre-planetary nebula IRAS 08005-2356 (I 08005) with an angular resolution of ∼1″–5″, using the Submillimeter Array, in the {sup 12}CO J = 2–1, 3–2, {sup 13}CO J = 2–1, and SiO J = 5–4 (v = 0) lines. Single-dish observations, using the SMT 10 m, were made in these lines as well as in the CO J = 4–3 and SiO J = 6–5 (v = 0) lines. The line profiles are very broad, showing the presence of a massive (>0.1 M{sub ⊙}), extreme high velocity outflow (V ∼ 200 km s{sup −1}) directed along the nebular symmetry axis derived from the Hubble Space Telescope imaging of this object. The outflow's scalar momentum far exceeds that available from radiation pressure of the central post-AGB star, and it may be launched from an accretion disk around a main-sequence companion. We provide indirect evidence for such a disk from its previously published, broad Hα emission profile, which we propose results from Lyβ emission generated in the disk followed by Raman-scattering in the innermost regions of a fast, neutral wind.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

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↗
DOE OSTI2011

Deterministic generation of a pair of entangled guided photons from a single atom in a nanofiber cavity

We investigate the controlled production of entangled guided photons. The technique is based on a two-stage vacuum-stimulated Raman process with a single atom in a nanofiber cavity. We examine the dependences of the two-photon emission probability and the entanglement concurrence on various parameters of the system, such as the radial and axial positions of the atom, the intensities and durations of the pump pulses, the one- and two-photon detunings, the cavity finesse, and the separation time between the pump pulses. We find that, due to the confinement of the guided cavity field in the transverse plane of the fiber and in the space between the cavity mirrors, the probability of generation of a pair of entangled guided photon can be high even when the finesse of the nanofiber cavity is moderate.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Gain-assisted control of the Goos-Haenchen shift

A gain-assisted model is considered to study the Goos-Haenchen (GH) shift behavior in the reflected and transmitted light. In this model, a probe light is incident on a cavity containing three-level dilute gaseous atomic medium. The atom-field interaction follows two-photon Raman transitions, and the dielectric susceptibility of the medium exhibits dispersion and gain properties [L. J. Wang, A. Kuzmich, and A. Dogariu, Nature (London) 406, 227 (2000)]. Under appropriate conditions, two gain peaks are observed with anomalous dispersion between the peaks, whereas normal dispersion can be observed at and around the gain maxima. The manipulation of the detuning associated with the probe light field which interacts with the intracavity medium during its propagation through the cavity can lead to a control over negative and positive GH shift in the reflected and transmitted light beam via the anomalous and normal dispersion of the medium.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Phase transitions and dark-state physics in two-color superradiance

We theoretically study an extension of the Dicke model, where the single-particle Hamiltonian has three energy levels in Lambda configuration (i.e., the excited state is coupled to two nondegenerate ground states via two independent quantized light fields). The corresponding many-body Hamiltonian can be diagonalized in the thermodynamic limit with the help of a generalized Holstein-Primakoff transformation. Analyzing the ground-state energy and the excitation energies, we identify one normal and two superradiant phases, separated by phase transitions of both first and second oder. A phase with both superradiant states coexisting is not stable. In addition, in the limit of two degenerate ground states a dark state emerges, which seems to be analogous to the dark state appearing in the well-known stimulated Raman adiabatic passage scheme.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

Spectroscopic prescription for optimal stimulated Raman transfer of ultracold heteronuclear molecules to the lowest rovibronic level

We show that the multiplicative product of a molecular-beam excitation spectrum and an ultracold-molecule excitation spectrum, with a frequency offset appropriate to the initial ultracold-molecule level, provides the relative rate of stimulated Raman transfer (SRT) from a given high rovibrational level to the lowest rovibronic level, i.e., the v{sup ''}=0,J{sup ''}=0 level of the ground electronic state for photoassociated (and magnetoassociated) ultracold molecules. This product spectrum clearly indicates the optimal pathways for SRT, even when the two component spectra are completely unassigned. We illustrate this specifically for the case of KRb.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Conservation of the photon number in the generalized nonlinear Schroedinger equation in axially varying optical fibers

We reexamine the derivation of the generalized nonlinear Schroedinger equation in the case of nonaxially uniform optical fibers, taking into account the longitudinal and spectral evolutions of all pertinent linear parameters. Our theory leads to an improved form of this equation that highlights an additional term, which ensures the conservation of the total photon number in nonuniform optical fibers in the absence of attenuation. Numerical simulations confirm the validity of this theory in the context of a Raman-induced soliton self-frequency shift, emission of Cherenkov radiation, and a soliton blue shift.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

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↗