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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 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Coherent Reaction between Molecular and Atomic Bose-Einstein Condensates: Integrable Model

Here, we solve a model that describes a stimulated conversion between ultracold bosonic atoms and molecules. The reaction is triggered by a linearly time-dependent transition throughout the Feshbach resonance. Our solution predicts a dependence, with a dynamic phase transition, of the reaction efficiency on the transition rate for both atoms-to-molecule pairing and molecular dissociation processes. We find that for the latter process with a linear energy dispersion of atomic modes, the emerging phase can have a thermalized energy distribution of noninteracting bosons with the temperature defined by the rate of the transition. This provides a simple interpretation of the phase transition in terms of the creation of equilibrium Bose-Einstein condensate.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2024

Persistence of Spin Coherence in a Crystalline Environment

Here, we analyze quantum interference in the triplet-exciton pair generated by singlet exciton fission in a molecular crystal and introduce transport-induced dephasing (TID) as a key effect that can suppress the expected fluorescence quantum beats when the triplet-exciton wave function can localize on inequivalent sites. TID depends on the triplet-exciton hopping rate between inequivalent sites and on the energy shifts among the stationary states of the entangled triplet pair in different spatial configurations. The theoretical model is confirmed by experiments in rubrene single crystals, where triplet pairs remain entangled for more than 50 ns but quantum beats are suppressed by TID within a few nanoseconds when the magnetic field is misaligned by just a few degrees from specific symmetric directions. Our experiments deliver the zero-field parameters for the rubrene molecule in its orthorhombic lattice and information on triplet-exciton transport, in particular, the triplet-exciton hopping rate between inequivalent sites, which we evaluate to be of the order of 150 ps in rubrene.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Three-dimensional coherent Bragg imaging of spontaneously rotating nanoparticles

This dataset contains spontaneous rocking curves of individual 60 nm gold particles, measured as CDI patterns in the Bragg geometry. The dataset provides a higher-quality alternative to ID 151, and is collected at lower energy, shorter detector distance (~120 mm) and using a He-filled flight tube. Additionally, this data includes measurements along the (111), (200), and (220) directions, providing access to multiple strain directions.

60 nm truncated-octrahedral gold nanoparticles↗
DOE OSTI2022

Nearly degenerate two-color impulsive coherent Raman hyperspectral imaging

Impulsive stimulated Raman scattering (ISRS) is a robust technique for studying low frequency (<300 cm –1 ) Raman vibrational modes, but ISRS has faced difficulty in translation to an imaging modality. A primary challenge is the separation of the pump and probe pulses. Here we introduce and demonstrate a simple strategy for ISRS spectroscopy and hyperspectral imaging that uses complementary steep edge spectral filters to separate the probe beam detection from the pump and enables simple ISRS microscopy with a single-color ultrafast laser source. ISRS spectra are obtained that span from the fingerprint region down to <50 cm –1 vibrational modes. Furthermore, hyperspectral imaging and polarization-dependent Raman spectra are also demonstrated.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

Laser-Produced Coherent X-ray Sources. Final report

This is the final report for the DOE-AMO DE-FG02-05ER15663 grant. Using a high-peak-power laser system at the Extreme Light Laboratory of the University of Nebraska-Lincoln, we develop novel femtosecond radiation sources and use them to investigate ultrafast photo-induced processes. Pulses of high energy electrons and x-rays are generated when an optical pulse is focused to ultra-high intensity. The radiation is used to probe the evolution of matter under highly non-equilibrium conditions with atomic-scale temporal and spatial resolution. Moreover, the facility is small enough to fit in a university laboratory and is operated by graduate students and postdocs.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2025

On the Structure–Property Relationship of Semi‐Coherent FeCr 2 O 4 /Cr 2 O 3 Spinel/Corundum Interfaces

Abstract Oxide heterointerfaces are extremely common in both natural and artificial composite structures, including corroded structural materials. Often, key properties such as segregation and atomic transport are dictated by the structure of these interfaces. However, despite this critical link, very few heterointerfaces have been studied in any detail at the atomic scale. Here, one important oxide heterointerface is examined, between spinel and corundum, using the chemical system FeCr 2 O 4 /Cr 2 O 3 as a representative and technologically important case. Using atomistic simulation techniques, it is found that the structure, particularly the local chemistry, of the interface depends on the crystal chemistry at the interface. This atomic and chemical structure further impacts important properties such as defect segregation and mass transport. It is found that defects can nucleate at some regions of these interfaces and migrate back and forth across the corundum layer, suggesting high atomic mobility that may be important for the evolution of spinel/corundum composite structures in extreme conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Coherent Manipulation of Single Electrons with Optical Photons in Condensed Helium-4

Single electrons are one of the simplest quantum objects in nature. In free space or conventional materials, single electrons hardly interact with optical (ultraviolet-visible-infrared) photons, so their quantum states cannot be easily manipulated by optics. Here, a notable exception is is theoretically demonstrated: A single electron in condensed helium-4 can be self-confined in a nanometric bubble of 1 to 2 nm radius and resonantly interact with mid-infrared photons of 3 to 12 μm wavelength. A femtosecond laser can drive the electron into Rabi oscillations and prepare it onto arbitrary superposition states between the ground and excited states. After the laser pulse, the electron bubble can exhibit remarkable nonequilibrium quantum dynamics and evolve toward various final states with various lifetimes. These processes are accompanied with intense phonon radiation.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Orbit averaging coherent states: holographic three-point functions of AdS giant gravitons

We study correlation functions of two AdS giant gravitons in AdS 5 × S 5 and a BPS supergravity mode using holography. In the gauge theory these are described by BPS correlators of Schur polynomials of fully-symmetric representations and a single trace operator. We find full agreement between the semiclassical gravity and gauge theory computations at large N, for both diagonal and off-diagonal structure constants. Our analysis in $\mathcal{N}$ = 4 SYM provides a simpler derivation to the results in the literature, and it can be readily generalized to operators describing bound states of AdS giant gravitons as well as bubbling geometries.

1/N Expansion↗