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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
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Large Non‐Resonant Infrared Optical Second Harmonic Generation in Bulk Crystals of Van der Waals Semiconductor, SnP 2 Se 6

2D van der Waals (vdW) materials have emerged as a highly promising candidates for nonlinear optical (NLO) applications. This study presents the synthesis, comprehensive linear optical, and optical second harmonic generation (SHG) characterization of a novel 2D vdW semiconductor SnP2Se6 in its bulk single crystal form. It exhibits an indirect bandgap of ≈1.47 eV and an exceptional non-resonant SHG coefficient of d 33 ∼ −222 ± 30 pm V −1 at a fundamental wavelength of 2 µm, which is ≈7 times larger than that of the commercial AgGaSe 2 with a comparable bandgap. Density functional theory (DFT) calculations of the linear and nonlinear optical properties exhibit reasonable agreement with the experimental measurements, revealing the chemical origin of the enhanced properties. Moreover, SnP 2 Se 6 can exhibit both type-I and type-II phase matching over a wide spectral range, fulfilling one of the key criteria for an ideal NLO crystal. These exceptional properties position SnP 2 Se 6 as a highly promising candidate for NLO applications.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Coupling buried etalon layers to an engraved metasurface for durable and large-aperture meta-optics

Many optical applications that could potentially benefit from the design flexibility provided by the metasurface approach are being prohibited by the limited scalability of the fabrication and the robustness of the end-result structures when using a resonant meta-elements-based approach. In this study, an alternative demonstrated approach with superior scalability and robustness is substrate-engraved metasurfaces, based on medium mixing homogenization, yet it suffers from very limited optical response. Here we propose advancing this approach by coupling the metasurface with buried etalon layers, leading to enhancement in the optical response. A transfer matrix analysis is used to study the parameter space, predicting that the patterned reflectance values range of a beam shaper could be raised from only 4% to 30% when the metasurface is engraved in silica, and even up to 66% when engraved into higher-index oxides. Using the method proposed here, the phase difference range across the metasurface could be increased by 0.4 radians beyond the range achievable by a metasurface engraved in silica and could reach even higher values when embedded in higher-index materials. Full-wave numerical simulations are used to demonstrate a cylindrical metareflector and a metalens, further validating the analysis.

47 OTHER INSTRUMENTATION↗
DOE OSTI2024

Impact of fused silica debris shields and enhanced mitigation techniques on large-aperture beam-sampling optics for the National Ignition Facility

Here, we show that the large-scale routine use of the fused silica debris shield (FSDS) maintains the ∼100× reduction in damage initiation rate and 70% increase in the install lifetime of a new grating debris shield (GDS) observed during pilot operations. Furthermore, we show that the install lifetimes of recycled GDS optics are nearly tripled using additional mitigation strategies such as expanding mitigation processing to include all damage sites larger than 10 μm (LT10) rather than just larger than 50 μm (LT50) and FSDS. We note that there is still a 50% difference between new and recycled optic installation lifetimes. We show that recycled optics have a 3.5× higher apparent initiation rate than new optics when exposed to nominally identical laser conditions.

FSDS↗
DOE OSTI2023

Time-varying gradient metasurface with applications in all-optical beam steering

Integrating the large, subpicosecond nonlinear optical response of epsilon-near-zero (ENZ) materials with the broad design freedoms of plasmonic metasurfaces shows potential for creating rapidly modulated optical devices with possible applications in telecommunications, sensing, and reactive beam steering. In this work, we experimentally investigate a metasurface consisting of a plasmonic gradient array on a thin layer of indium tin oxide (ITO), characterize how incident probe pulses diffract from a system as it is being dynamically modulated by a pump pulse at wavelengths near the ENZ region. Angular shifts in the diffraction orders are observed and can be principally attributed to the adiabatic wavelength conversion of the probe as it witnesses the temporal change of index induced by the pump. Of note, the asymmetric gradient metasurface, considered to be a blazed diffraction grating, shows significantly different dynamic responses for different diffraction orders. The free-space wavelength shift to +1 and -1 diffraction orders is 6 and 12 nm, resulting in steering angle changes of 0.65 and 1.5°, respectively.

42 ENGINEERING↗
DOE OSTI2024

Optical Properties of Low‐Defect Large‐Area Hexagonal Boron Nitride for Quantum Applications

Intrinsic defects and their concentrations in hexagonal boron nitride (h-BN) play a key role in single-photon emission. In this study, the optical properties of large-area multilayer h-BN-on-sapphire grown by metal-organic chemical vapor deposition are explored. Based on the detailed spectroscopic characterization using both cathodoluminescence (CL) and photoluminescence (PL) measurements, the material is devoid of random single-point defects instead of a few clustered complex defects. The emission spectra of the measurements confirm a record-low-defect concentration of ≈10 4 cm −2 . Post-annealing, no significant changes are observed in the measured spectra and the defect concentrations remain unaltered. Through CL and PL spectroscopy, an optically active boron vacancy spin defect is identified and a novel complex defect combination arising from carbon impurities is revealed. This complex defect, previously unreported, signifies a unique aspect of the material. In these findings, the understanding of defect-induced optical properties in h-BN films is contributed, providing insights for potential applications in quantum information science.

42 ENGINEERING↗
DOE OSTI2021

Radically Tunable n-Type Organic Semiconductor via Polymorph Control

Polymorphism has emerged as an important design consideration in organic semiconductors (OSCs). Previously, in many OSCs, even small changes in molecular stacking can cause drastic changes to the optical and electronic properties. However, investigation into n-type semiconductors has significantly lagged behind their p-type counterparts. In this work, we present the prolific polymorphism of 2-dimensional quinoidal terthiophene (2DQTT-o-B) and systematically investigate each of 5 polymorphs, 3 of which have been previously unreported. Grazing incidence X-ray diffraction provided a key method to understanding the structure of each polymorph. Via the polymorphic transitions mapped, we tuned the electron mobility by 5 orders of magnitude, from 5.63 × 10 –5 to 0.22 cm 2 V –1 s –1 . These were accompanied by modifications to the optical properties, namely we observed substantial differences in the refractive index noted by intensity differences under polarized optical microscopy and a large shift in optical band gap from 1.18 eV up to 1.40 eV. Lastly, we suggest that changes to these properties may be related to the unique quinoidal to aromatic transition observed in quinoidal molecules.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Large Language Model for Validation, Optical Calibration, and Learning (VOCAL) Distributed Temperature Sensing Interface

Distributed temperature sensing (DTS) using fiber optic sensors (FOS) offers a promising method for temperature measurements in advanced reactors, such as sodium fast reactors and molten salt cooled reactors. To support the calibration and validation of DTS measurements, Argonne National Laboratory developed the Validation, Optical Calibration, and Learning (VOCAL) software package. This report describes the integration of a local large language model (LLM) with a retrieval-augmented generation (RAG) system into the VOCAL interface to serve as an interactive user assistant. The LLM framework enhances the VOCAL platform’s accessibility to users by explaining interface components, clarifying inputs and outputs, and answering user queries dynamically in real-time. The accuracy of the LLM assistant performance was evaluated with 20 queries regarding the interface and its parameters using experimental data from the Thermal Hydraulic Experimental Test Article (THETA) facility. Results demonstrate that the LLM achieved a 95% accuracy rate, with a BERTScore of 0.8816 and SBERT value of 0.7417. Furthermore, validation of the RAG system within the LLM framework showed optimal accuracy with k-values between 1 and 2 using the k-refinement convergence test. The prompt perturbation analysis demonstrated good initial consistency for the RAG system, exhibiting the highest accuracy under punctuation variations and the greatest sensitivity under query reordering. Notably, the model’s errors were limited to data retrieval failures rather than factual hallucinations, reinforcing its baseline reliability. The integration of LLM provides a highly accurate, userfriendly enhancement to the VOCAL platform without disrupting its core computational capabilities for FOS calibration and validation.

Hong, Evan↗
DOE OSTI2022

Second Target Station Project (STS) Steerable Optic Design & Testing Report

Multiple neutron scattering instrument concepts for the Spallation Neutron Source's Second Target Station (STS) incorporate advanced neutron optic designs which incorporate discrete mirrors rather than continuous neutron guides that were the standard for instruments in the First Target Station. These mirrors can be a few to several meters in length and must be stably supported and aligned as a single optic. In addition, due to the length of the STS instruments and the small size of the STS neutron beams, installation and alignment at the micron level of precision will be required, which is beyond the ability of today's survey & alignment technology. Thus, a means of remotely adjusting these mirrors with single digit micron resolution is needed. A Steerable Optic System was designed to provide the precision and resolution required to support and manipulate these large, heavy optics under beamline shielding. A mockup was developed to demonstrate and validate this system for use in neutron optic applications, and this document describes the design and testing results of that mockup.

43 PARTICLE ACCELERATORS↗
DOE OSTI2025

Solving tricky quantum optics problems with assistance from large language models

The capabilities of modern artificial intelligence (AI) as a “scientific collaborator” are explored by engaging it with three nuanced problems in quantum optics: state populations in optical pumping, resonant transitions between decaying states (the Burshtein effect), and degenerate mirrorless lasing. Through iterative dialogue, the authors observe that AI models–when prompted and corrected–can reason through complex scenarios, refine their answers, and provide expert-level guidance, closely resembling the interaction with an adept colleague. The findings highlight that AI can democratize access to sophisticated modeling and analysis, shifting the focus in scientific practice from technical mastery to the generation and testing of ideas, and reducing the time for completing research tasks from days to minutes.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2022

AutoEnRichness: A hybrid empirical and analytical approach for estimating the richness of galaxy clusters

ABSTRACT We introduce AutoEnRichness, a hybrid approach that combines empirical and analytical strategies to determine the richness of galaxy clusters (in the redshift range of 0.1 ≤ z ≤ 0.35) using photometry data from the Sloan Digital Sky Survey Data Release 16, where cluster richness can be used as a proxy for cluster mass. In order to reliably estimate cluster richness, it is vital that the background subtraction is as accurate as possible when distinguishing cluster and field galaxies to mitigate severe contamination. AutoEnRichness is comprised of a multistage machine learning algorithm that performs background subtraction of interloping field galaxies along the cluster line of sight and a conventional luminosity distribution fitting approach that estimates cluster richness based only on the number of galaxies within a magnitude range and search area. In this proof-of-concept study, we obtain a balanced accuracy of 83.20 per cent when distinguishing between cluster and field galaxies as well as a median absolute percentage error of 33.50 per cent between our estimated cluster richnesses and known cluster richnesses within r200. In the future, we aim for AutoEnRichness to be applied on upcoming large-scale optical surveys, such as the Legacy Survey of Space and Time and Euclid, to estimate the richness of a large sample of galaxy groups and clusters from across the halo mass function. This would advance our overall understanding of galaxy evolution within overdense environments as well as enable cosmological parameters to be further constrained.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Beyond Graphene: Low-Symmetry and Anisotropic 2D Materials

Low-symmetry 2D materials—such as ReS 2 and ReSe 2 monolayers, black phosphorus monolayers, group-IV monochalcogenide monolayers, borophene, among others—have more complex atomistic structures than the honeycomb lattices of graphene, hexagonal boron nitride, and transition metal dichalcogenides. The reduced symmetries of these emerging materials give rise to inhomogeneous electron, optical, valley, and spin responses, as well as entirely new properties such as ferroelasticity, ferroelectricity, magnetism, spin-wave phenomena, large nonlinear optical properties, photogalvanic effects, and superconductivity. Novel electronic topological properties, nonlinear elastic properties, and structural phase transformations can also take place due to low symmetry. Lastly, the “Beyond Graphene: Low-Symmetry and Anisotropic 2D Materials” Special Topic was assembled to highlight recent experimental and theoretical research on these emerging materials.

2D materials↗
DOE OSTI2022

A poloidal high- k scattering system for NSTX-U

A previous 5-channel tangential high-k scattering system is being replaced by an 8-channel, poloidal high-k scattering system on the National Spherical Torus eXperiment Upgrade (NSTX-U) device located in Princeton, NJ, USA. The 693 GHz poloidal scattering system replaces a 280 GHz tangential scattering system to study high-k electron density fluctuations on NSTX-U, thereby considerably enhancing planned turbulence physics studies by providing a measurement of the k θ -spectrum of both electron temperature gradient (ETG) and ion temperature gradient (ITG) modes. Two approaches to generating the 693 GHz probe beam are under development: an optically-pumped far-infrared (FIR) laser that generates ~50 mW, and a compact gyrotron that can potentially generate in excess of 5 W. Large aperture optics collect radiation scattered from density fluctuations in the plasma core at 8 simultaneous scattering angles ranging from 2 to 15° corresponding to poloidal wavenumbers that extend to >40 cm -1 . Finally, steerable launch optics coupled with receiver optics mounted on a 5-axis receiver carriage allow the scattering volume to be placed radially from r/a = 0.3 out to the pedestal region (r/a ~ 0.99) and translated horizontally as needed to satisfy wavenumber matching.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

Robustness of Optical Response for Self-Assembled Plasmonic Metamaterials with Morphological Disorder and Surface Roughness

Bottom-up fabrication of metallized biotemplated nanostructures to form specific plasmonic nanoresonators holds promise as a means of achieving large-scale optical metamaterials. However, in contrast to top-down methods, the stochastic growth of self-assembled nanoresonators is prone to significant disorder and surface roughness, which naturally raise an important question about the robustness of their resonant properties in terms of structural imperfections. An aggregated-random-sphere model is developed to mimic the nucleated growth of metallized DNA origami assembly, leading to meta-atoms with realistic, experimentally observed morphological disorder and surface roughness. Using the well-known split-ring-resonator (SRR) motif as an example, the resonant properties of meta-atoms under different levels of roughness are investigated and a strong tolerance of optical response against morphological disorder is revealed. It is found that in SRRs, even with dramatic roughness introduced, the expected resonances are still observed, despite broadening line shapes compared to ideal smooth structure. Only for extreme disorder, which causes drastic segmentation of SRRs, does the resonant response disappear. Finally, the demonstrations are very encouraging for the prospects of bottom-up fabrication toward versatile functional metamaterials and metadevices.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Freeform three-mirror anastigmatic large-aperture telescope and receiver optics for CMB-S4

CMB-S4, the next-generation ground-based cosmic microwave background (CMB) observatory, will provide detailed maps of the CMB at millimeter wavelengths to dramatically advance our understanding of the origin and evolution of the universe. CMB-S4 will deploy large and small aperture telescopes with hundreds of thousands of detectors to observe the CMB at arcminute and degree resolutions at millimeter wavelengths. Inflationary science benefits from a deep delensing survey at arcminute resolutions capable of observing a large field of view at millimeter wavelengths. This kind of survey acts as a complement to a degree angular resolution survey. The delensing survey requires a nearly uniform distribution of cameras per frequency band across the focal plane. We present a large-throughput, large-aperture (5-meter diameter) freeform three-mirror anastigmatic telescope and an array of 85 cameras for CMB observations at arcminute resolutions, which meets the needs of the delensing survey of CMB-S4. A detailed prescription of this three-mirror telescope and cameras is provided, with a series of numerical calculations that indicate expected optical performance and mechanical tolerance.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

High-efficiency optical limiter using metasurface and phase-change material

According to some aspects, a transmissive and all-dielectric optical component/limiter with great cutoff efficiency using Vanadium Dioxide (VO 2 ) as the active component is disclosed. In some embodiments, Vanadium dioxide is used for an optical limiter due to the large contrast in optical constants upon undergoing the semiconductor to metal phase transition. When triggered optically, this transition occurs within 60 fs, making the device suitable for an ultrafast laser environment. In addition, the phase transition threshold is tunable by applying stress or doping; therefore, the device cutoff intensity can be adjusted to fulfill specific requirements.

Valentine, Jason G.↗
DOE OSTI2023

Optical stark effect on CdSe nanoplatelets with mid-infrared excitation for large amplitude ultrafast modulation

The optical Stark effect is a universal response of the electronic structure to incident light. In semiconductors, particularly nanomaterials, the optical Stark effect achieved with sub-band gap photons can drive large, narrowband, and potentially ultrafast changes in the absorption or reflection at the band gap through excitation of virtual excitons. Rapid optical modulation using the optical Stark effect is ultimately constrained, however, by the generation of long-lived excitons through multiphoton absorption. This work compares the modulation achievable using the optical Stark effect on CdSe nanoplatelets with several different pump photon energies, from the visible to mid-infrared. Despite expected lower efficiencies for spectrally-remote pump energies, infrared pump pulses can ultimately drive larger sub-picosecond optical Stark shifts of virtual excitons without creation of real excitons. Importantly, the CdSe nanoplatelets show subpicosecond shifts of the lowest excitonic resonance of up to 22 meV, resulting in change in absorption as large as 0.32 OD (49% increase in transmission), with a long-lived offset from real excitons less than 1% of the peak signal.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Grating-Based Imaging-Scattering with Portable Neutron Generator

Company: Adelphi Technology, Inc. Title: Grating-Based Imaging-Scattering with Portable Neutron Generator PI: Dr. Jay Theodore Cremer, Jr. Topic: 26a Statement of the problem or situation that is being addressed. Successful plant growth depends upon an efficient and robust root system. The plant root is part of a larger system of water and microbial flows in the soil system. While much effort has been exerted to develop an imaging system for water, microbes, and roots, the problem is challenging, and no widely accepted imaging method currently exists. The optical solutions use a highly modified soil system. X-ray imaging methods are insensitive to the soft tissues in the presence of sand. Thermal neutron imaging has been often tested, but found inadequate, due to limited access and low image resolution. This project will develop a new strategy for neutron imaging of plant/soil systems. The project will allow long duration experiments in greenhouse environments and increase the image information content to the micron scale. General statement of how this problem is being addressed. Portable, rugged thermal and fast neutron sources are being developed where portable means a two-soldier team can carry the source and power unit to survey rough terrain for explosives. In the past decade, microfabrication of X-ray and thermal/cold neutron optics has opened a new imaging strategy. The standard transmission image is now supplemented with simultaneous acquisition of a phase contrast image and an image revealing scattering features. In materials science, the interferometric neutron scattering image has been used to detect early crack formation in stressed additive manufacturing test samples. The detection requires sensitivity to scattering features at the 1-micron scale. By addition of our proposed grating-optic to Adelphi Technology’s radiographic/tomographic imaging system, which is based on portable thermal neutron source, the resulting thermal neutron scatter image of the plant/soil system, will reveal details at 1-micron. Commercial Applications and Other Benefits Neutron interferometry imaging has greater penetration through large metal components compared to industrial X-ray imaging. The low-cost, large area optics developed for greenhouse applications, combined with the robust, portable neutron generator, can then be marketed as a system for inspection of additive manufactured components. In the aerospace industry, all freshly printed components are validated with X-ray CT. Scheduled maintenance again requires X-ray CT as the ability to predict aerospace component lifetime does not yet exist. Large aerospace components are only partially observed with X-ray imaging. Key Words Neutron radiography/tomography, grating interferometry, thermal neutron generator imaging, plant root and soil imaging, rhizosphere imaging, deployable neutron imaging systems Summary for Members of Congress A rugged, portable source of thermal neutrons is adapted for neutron interferometry imaging with the addition of low-cost, 3D printed optics. The first application of our proposed deployable, compact thermal neutron generator imaging system, using a grating optic, is plant root/soil science in greenhouse settings and agricultural laboratories.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Bulk Photovoltaic Effect Driven by Collective Excitations in a Correlated Insulator

We investigate the bulk photovoltaic effect, which rectifies light into electric current, in a collective quantum state with correlation driven electronic ferroelectricity. We show via explicit real-time dynamical calculations that the effect of the applied electric field on the electronic order parameter leads to a strong enhancement of the bulk photovoltaic effect relative to the values obtained in a conventional insulator. The enhancements include both resonant enhancements at sub-band-gap frequencies, arising from excitation of optically active collective modes, and broadband enhancements arising from nonresonant deformations of the electronic order. The deformable electronic order parameter produces an injection current contribution to the bulk photovoltaic effect that is entirely absent in a rigid-band approximation to a time-reversal symmetric material. Furthermore, our findings establish that correlation effects can lead to the bulk photovoltaic effect and demonstrate that the collective behavior of ordered states can yield large nonlinear optical responses.

14 SOLAR ENERGY↗