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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 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Phase-resolving spin-wave microscopy using infrared strobe light

The need for sensitively and reliably probing magnetization dynamics has been increasing in various contexts such as studying novel hybrid magnonic systems, in which the spin dynamics strongly and coherently couple to other excitations, including microwave photons, light photons, or phonons. Recent advances in quantum magnonics also highlight the need for employing the magnon phase as quantum state variable, which is to be detected and mapped out with high precision in on-chip micro- and nanoscale magnonic devices. Here, in this study, we demonstrate a facile optical technique that can directly perform concurrent spectroscopic and imaging functionalities with spatial and phase resolutions, using infrared strobe light operating at 1550-nm wavelength. To showcase the methodology, we spectroscopically studied the phaseresolved spin dynamics in a bilayer of Permalloy and yttrium iron garnet Y 3 Fe 5 O 12 (YIG), and spatially imaged the backward-volume spin-wave modes of YIG in the dipolar spin-wave regime. Using the strobe light probe, the detected precessional phase contrast can be directly used to construct the map of the spin wave's wave front, in the continuous-wave regime of spin-wave propagation and in the stationary state, without needing any optical reference path. By selecting the applied field, frequency, and detection phase, the spin-wave images can be made sensitive to the precession amplitude and phase. Our results demonstrate that infrared optical strobe light can serve as a versatile platform for magneto-optical probing of magnetization dynamics, with potential implications in investigating hybrid magnonic systems.

Xiong, Yuzan [University of North Carolina, Chapel↗
DOE OSTI2018

Annealing induced microstructure engineering of antimony tri-selenide thin films

Highlights: • Deposition of Sb{sub 2}Se{sub 3} thin films using thermal vapour deposition. • Films are deposited on substrates with concurrent heating and without heating. • Effect of post deposition annealing on the two types of films are investigated. • Influence of temperature and processing conditions on optical band gap are probed. • This Sb{sub 2}Se{sub 3} films can find application in solar cells and optoelectronic devices. - Abstract: The presented work demonstrates the effect of annealing on the structural, surface morphology and optical properties of Antimony Triselenide (Sb{sub 2}Se{sub 3}) thin films deposited by thermal evaporation. Two sets of thin films of Sb{sub 2}Se{sub 3} were grown on soda lime glass (SLG) substrates by thermal evaporation with and without substrate heating. Both sets of films were then annealed at three distinct temperatures (100 °C, 200 °C and 300 °C) to study the effects of annealing on the microstructure. Analysis using XRD (X-Ray Diffraction) characterization revealed that the as-deposited films without substrate heating exhibit an amorphous nature, whereas the films grown with concurrent substrate heating are polycrystalline with orthorhombic structure. The films annealed at high temperature with concurrent substrate heating possess smooth and continuous grain morphologies. The effect of annealing was also found to have significant impact on the band gap and optical properties of the Sb{sub 2}Se{sub 3} thin films.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Nonlinear processes upon two-photon interband picosecond excitation of PbWO{sub 4} crystal

A new experimental method is proposed to study the dynamics of nonlinear processes occurring upon two-photon interband picosecond excitation of a lead tungstate crystal and upon its excitation by cw probe radiation in a temporal range from several nanoseconds to several seconds. The method is applied to the case of crystal excitation by a sequence of 25 high-power picosecond pulses with a wavelength of 523.5 nm and 633-nm cw probe radiation. Measuring the probe beam transmittance during crystal excitation, one can investigate the influence of two-photon interband absorption and the thermal nonlinearity of the refractive index on the dynamics of nonlinear processes in a wide range of times (from several nanoseconds to several seconds). The time resolution of the measuring system makes it possible to distinguish fast and slow nonlinear processes of electronic or thermal nature, including the generation of a thermal lens and thermal diffusion. An alternative method is proposed to study the dynamics of induced absorption transformation and, therefore, the dynamics of the development of nonlinear rocesses upon degenerate two-photon excitation of the crystal in the absence of external probe radiation. (nonlinear-optical phenomena)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Time-resolved, nonequilibrium carrier and coherent acoustic phonon dynamics in (Cd, Mg)Te single crystals for radiation detectors

We present time-resolved nonequilibrium carrier and coherent acoustic phonon dynamics in (Cd, Mg)Te single crystals intended for detection of high-energy x-ray photons. Our (Cd, Mg)Te crystals were grown using a vertical Bridgman method and during the process were doped either with In (a shallow dopant) or Ge (a deep impurity). Next they were cut into platelets and, subsequently, tested as as-grown specimens, or, before testing, long-term annealed in a temperature range of 750 °C–800 °C to improve their crystalline properties. All samples exhibited high resistivities of 10 9 –10 10 Ω cm, as required for x-ray detection applications. We have performed femtosecond optical spectroscopy, pump-probe measurements on all samples in both one-color (high-intensity 800 nm pump and low-intensity 800 nm probe) and two-color (high-intensity 400 nm pump and low-intensity 800 nm probe) configurations, and analyzed the results using our carrier dynamics rate-equation model. The model allowed us to perform a comprehensive, time-resolved analysis of relaxation dynamics of photoexcited carriers and investigate the role of carrier traps present in all tested samples. Two-color measurements also allowed us to observe and analyze the propagation of acoustic coherent phonons excited by the high-energy pump pulse. We observed that the dependence of phonon mode frequency, after including a correction of the experimentally measured crystal index of refraction dependence on the probe wavelength, was dispersionless and led to the value for the sound velocity of 3367 m s –1 , which is in excellent agreement with the literature data. The intrinsic lifetime of coherent phonons in (Cd, Mg)Te was estimated to be of the order of 10 ns. Lastly, we conclude that among our tested samples, the In-doped, annealed (Cd, Mg)Te crystal exhibits the best characteristics for radiation detection applications.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Excited-State Charge Distribution of a Donor–π–Acceptor Zn Porphyrin Probed by N K-Edge Transient Absorption Spectroscopy

Zinc porphyrin solar cell dyes with donor-π–acceptor architectures combine light absorber (π), electron-donor, and electron-acceptor moieties inside a single molecule with atomic precision. The donor-π–acceptor design promotes the separation of charge carriers following optical excitation. Here, we probe the excited-state electronic structure within such molecules by combining time-resolved X-ray absorption spectroscopy at the N K-edge with first-principles time-dependent density functional theory (TD-DFT) calculations. Furthermore, customized Zn porphyrins with strong-donor triphenylamine groups or weak-donor tri-tert-butylbenzene groups were synthesized. Energetically well-separated N K-edge absorption features simultaneously probe the excited-state electronic structure from the perspectives of the macrocycle and triphenylamine N atoms. New absorption transitions between the macrocycle N atoms and the excited-state HOMO vacancy are observed, and the triphenylamine associated absorption feature blue-shifts, consistent with partial oxidation of the donor groups in the excited state.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Brain sensor and communication model using plasmonic microring antenna network

In this paper, the feasibility of using multi-plasmonic sensing probes embedded nanoring resonators within a microring resonator system for brain signal probing and the investigation proposed. The plasmonic sensor probes made of gold grating placed within the center nanorings, from which the sensor network of the coupling light from the multi-plasmonic probes to the main ring established. The coupling between light (photon) power and nano-gold grating generate the plasmonic polariton dipoles and propagate within the system. The whispering gallery mode generates at the center rings, which will couple into the sensor probes and the induced change in optical signals that can detect via the system ports. The coupling between the generated polaritons and external stimuli from the sub-brain cells will change the optical output signals, where the electro-optic signal conversion can be applied. In manipulation, the changes in the grating periods of the sensing probes will affect the changes in the output signals, which can distinguish by the sensing probe signal Bragg wavelengths. The optical filter applied at each of the device port to attenuate the output signal that can be applied for brain investigation. The simulation results have shown that the low output power can detect for sub-level investigation.

42 ENGINEERING↗
DOE OSTI2020

Time-Resolved Ultrafast Transient Polarization Spectroscopy to Investigate Nonlinear Processes and Dynamics in Electronically Excited Molecules on the Femtosecond Time Scale

Here, we report a novel experimental technique to investigate ultrafast dynamics in photoexcited molecules by probing the third-order nonlinear optical susceptibility. A non-colinear 3-pulse scheme is developed to probe the ultrafast dynamics of excited electronic states using the optical Kerr effect by time-resolved polarization spectroscopy. Optical heterodyne and optical homodyne detection are demonstrated to measure the third-order nonlinear optical response for the S 1 excited state of liquid nitrobenzene, which is populated by 2-photon absorption of a 780 nm 35 fs excitation pulse.

47 OTHER INSTRUMENTATION↗
DOE OSTI2023

Revealing core-valence interactions in solution with femtosecond X-ray pump X-ray probe spectroscopy

Abstract Femtosecond pump-probe spectroscopy using ultrafast optical and infrared pulses has become an essential tool to discover and understand complex electronic and structural dynamics in solvated molecular, biological, and material systems. Here we report the experimental realization of an ultrafast two-color X-ray pump X-ray probe transient absorption experiment performed in solution. A 10 fs X-ray pump pulse creates a localized excitation by removing a 1 s electron from an Fe atom in solvated ferro- and ferricyanide complexes. Following the ensuing Auger–Meitner cascade, the second X-ray pulse probes the Fe 1 s → 3 p transitions in resultant novel core-excited electronic states. Careful comparison of the experimental spectra with theory, extracts +2 eV shifts in transition energies per valence hole, providing insight into correlated interactions of valence 3 d with 3 p and deeper-lying electrons. Such information is essential for accurate modeling and predictive synthesis of transition metal complexes relevant for applications ranging from catalysis to information storage technology. This study demonstrates the experimental realization of the scientific opportunities possible with the continued development of multicolor multi-pulse X-ray spectroscopy to study electronic correlations in complex condensed phase systems.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Extrinsic Nonlinear Kerr Rotation in Topological Materials under a Magnetic Field

Topological properties in quantum materials are often governed by symmetry and tuned by crystal structure and external fields, and hence, symmetry-sensitive nonlinear optical measurements in a magnetic field are a valuable probe. Here, we report nonlinear magneto-optical second harmonic generation (SHG) studies of nonmagnetic topological materials including bilayer WTe 2 , monolayer WSe 2 , and bulk TaAs. The polarization-resolved patterns of optical SHG under a magnetic field show nonlinear Kerr rotation in these time-reversal symmetric materials. For materials with 3-fold rotational symmetric lattice structure, the SHG polarization pattern rotates just slightly in a magnetic field, whereas in those with mirror or 2-fold rotational symmetry, the SHG polarization pattern rotates greatly and distorts. Further, these different magneto-SHG characters can be understood by considering the superposition of the magnetic field-induced time-noninvariant nonlinear optical tensor and the crystal-structure-based time-invariant counterpart. The situation is further clarified by scrutinizing the Faraday rotation, whose subtle interplay with crystal symmetry accounts for the diverse behavior of the extrinsic nonlinear Kerr rotation in different materials. Our work illustrates the application of magneto-SHG techniques to directly probe nontrivial topological properties, and underlines the importance of minimizing extrinsic nonlinear Kerr rotation in polarization-resolved magneto-optical studies.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Terahertz magneto-nanoscopy of encapsulated monolayer graphene

This study investigates the nanoscale conductivity of encapsulated monolayer graphene at temperatures down to 5 K and magnetic fields of up to 1 T. We use the scattering-type scanning near-field optical microscopy technique to probe magnetic-field-dependent responses from graphene close to charge neutrality in the terahertz spectral region. We observe the near-perfect high-q reflector behavior of graphene but with subtle changes by the presence of magnetic fields. Measurements align with calculations of the magneto-optical conductivity and the near-field spectroscopic contrast that describes the field-tunable cyclotron resonance of Dirac fermions. Our result provides an initial step toward understanding temperature and magnetic field effects on nanoscale terahertz transport in two-dimensional quantum materials.

Kim, Richard H. J. [Ames Laboratory (AMES), Ames, ↗
DOE OSTI2020

Probing and manipulating magnetic and 2D quantum materials using ultrafast laser and high harmonic sources

The ability to probe the full dynamic response of quantum materials on the length- and time-scales (Å to attoseconds on up) fundamental to charge, spin and phonon interactions is leading to a host of new discoveries. The coupled interactions between charges, spins, orbital and lattice degrees of freedom are key to determining the state of a material, whether metallic, insulating, superconducting or magnetic. Under thermal equilibrium conditions these states can be tuned by varying the temperature, pressure, chemical doping or dimensionality. However, their inherent complexity and rich phase landscape make them challenging to understand or manipulate deterministically. Fortunately, ultrafast light sources have undergone remarkable advances in recent years, achieving what was merely a dream three decades ago, i.e., full coherent control of light fields spanning the THz to the X-ray regions. Here, these new capabilities are providing powerful new tools for coherently manipulating and probing quantum materials using light. Recent advances in high harmonic generation (HHG) have provided new techniques for uncovering new phases and couplings in 2D and magnetic materials, using femtosecond lasers to coherently manipulate and tune the properties and interactions in the material, and HHG as a probe to map out these new phases and couplings. There are several beautiful recent observations of exciting new states in materials using light, but in some cases, the limited experimental data points made it challenging to validate an interpretation. The new ability of ultrafast HHG-based photoemission and magneto-optic spectroscopies to precisely probe multiple phases, electronic and magnetic order parameters, when combined with scanning the laser excitation fluence, is allowing us to map how material phases, magnetic states, and electron-phonon-spin couplings in these delicate materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

GALILEO: Galactic Axion Laser Interferometer Leveraging Electro-Optics

We propose a novel experimental method for probing light dark matter candidates. We show that an electro-optical material’s refractive index is modified in the presence of a coherently oscillating dark matter background. A high-precision resonant Michelson interferometer can be used to read out this signal. The proposed detection scheme allows for the exploration of an uncharted parameter space of dark matter candidates over a wide range of masses—including masses exceeding a few tens of microelectronvolts, which is a challenging parameter space for microwave cavity haloscopes. Published by the American Physical Society 2024

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Modulation of diode laser radiation for the formation of a distance-independent backscattered signal

We propose a probing regime, in which the backscattered signal energy is independent of the distance from the surface of a scattering object. This regime is implemented using a part of the laser radiation power. With respect to the efficiency of using the laser during one measurement, the proposed regime is close to the pseudorandom noise continuous wave lidar regime. Using diode lasers, the regime of the degenerate energy response function and the lidar regime can be implemented in a single device. The relations between the geometric parameters of the probing scheme and the modulation parameters of laser radiation are obtained. The dependence of the linearity range of the diode laser on the relation between the length of the receiving channel near-field zone and the length of the probed trace is substantiated. (control of laser radiation parameters)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Single detector laser-induced fluorescence imager and raman spectral instrument

Apparatus include divergence optics removably coupled to receive a probe beam in a first imaging mode to cause the probe beam to diverge before impinging on a first area of a target surface, and to not receive the probe beam in a second imaging mode to cause the probe beam to impinge on a second area of the target surface smaller than the first area, collection optics configured to receive, in response to the probe beam, luminescence light emitted from the first area and spectral light emitted from the second area, and an optical detector coupled to the collection optics, wherein the optical detector includes a luminescence imaging detector portion and a spectral imaging detector portion adjacent to the luminescence imaging detector portion, wherein the luminescence imaging detector portion is configured to receive the luminescence light emitted from the first area and the spectral imaging detector portion is configured to receive the spectral light from the second area.

Gasda, Patrick J.↗
DOE OSTI2018

Quantization of surface charge density on hyperboloidal and paraboloidal domains with application to plasmon decay rate on nanoprobes

We report that field quantization in high curvature geometries help understanding the elastic and inelastic scattering of photons and electrons in nanostructures and probelike metallic domains. The results find important applications in high-resolution photonic and electronic modalities of scanning probe microscopy, nano-optics, plasmonics, and quantum sensing. We present a calculation of relevant photon interactions in both hyperboloidal and paraboloidal material domains. The two morphologies are compared for their plasmon dispersion properties, field distributions, and radiative decay rates, which are shown to be consistent with the corresponding quantities for the finite prolate spheroidal domains. Finally, the results are relevant to other material domains that model a nanostructure such as a probe tip, quantum dot, or nanoantenna.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Optical trapping and control of nanoparticles inside evacuated hollow core photonic crystal fibers

We demonstrate an optical conveyor belt for levitated nanoparticles over several centimeters inside both air-filled and evacuated hollow-core photonic crystal fibers (HCPCF). Detection of the transmitted light field allows three-dimensional read-out of the particle center-of-mass motion. An additional laser enables axial radiation pressure based feedback cooling over the full fiber length. We show that the particle dynamics is a sensitive local probe for characterizing the optical intensity profile inside the fiber as well as the pressure distribution along the fiber axis. In contrast to some theoretical predictions, we find a linear pressure dependence inside the HCPCF, extending over three orders of magnitude from 0.2 mbar to 100 mbar. A targeted application is the controlled delivery of nanoparticles from ambient pressure into medium vacuum.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

THE EFFECTS OF DARK MATTER ANNIHILATION ON COSMIC REIONIZATION

We revisit the possibility of constraining the properties of dark matter (DM) by studying the epoch of cosmic reionization. Previous studies have shown that DM annihilation was unlikely to have provided a large fraction of the photons which ionized the universe, but instead played a subdominant role relative to stars and quasars. The DM might, however, have begun to efficiently annihilate with the formation of primordial microhalos at z ∼ 100–200, much earlier than the formation of the first stars. Therefore, if DM annihilation ionized the universe at even the percent level over the interval z ∼ 20–100, it could leave a significant imprint on the global optical depth, τ . Moreover, we show that cosmic microwave background polarization data and future 21 cm measurements will enable us to more directly probe the DM contribution to the optical depth. In order to compute the annihilation rate throughout the epoch of reionization, we adopt the latest results from structure formation studies and explore the impact of various free parameters on our results. We show that future measurements could make it possible to place constraints on the DM’s annihilation cross-sections, which are at a level comparable to those obtained from the observations of dwarf galaxies, cosmic-ray measurements, and studies of recombination.

79 ASTRONOMY AND ASTROPHYSICS↗