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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

From natural language to control signals: a conceptual framework for semantic channel finding in complex experimental infrastructure

Modern experimental platforms such as particle accelerators, fusion devices, telescopes, and industrial process control systems expose tens to hundreds of thousands of control and diagnostic channels, accumulated over decades of hardware evolution. Operators and AI systems alike depend on informal expert knowledge, inconsistent naming conventions, and scattered documentation to locate the signals required for monitoring, troubleshooting, and automated control, creating a persistent bottleneck for reliability, scalability, and emerging language-model-driven interfaces. We formalize semantic channel finding, the task of mapping natural-language intent to concrete control-system signals, as a general problem in complex experimental infrastructure, and introduce a four-paradigm conceptual framework to guide architecture selection based on facility-specific data regimes. The paradigms span (i) direct in-context lookup over small, curated channel dictionaries, (ii) constrained hierarchical navigation through structured trees, (iii) interactive agent exploration using iterative reasoning and tool-based database queries, and (iv) ontology-grounded semantic search that decouples channel meaning from facility-specific naming conventions. We demonstrate the practical feasibility of each paradigm through proof-of-concept implementations at four operational facilities spanning two orders of magnitude in scale: from compact free-electron lasers to large synchrotron light sources, operating under diverse control-system architectures ranging from clean hierarchical naming schemes to legacy environments with decades of heterogeneous conventions. Where evaluated against expert-curated operational queries, these instantiations achieve 90%–97% accuracy, validating the framework’s applicability across real-world deployment scenarios. To accelerate adoption across the broader scientific and industrial control-system community, we release open-source, plug-and-play implementations of all three interactive paradigms-direct lookup, hierarchical navigation, and middle-layer exploration-within the Osprey framework, together with tools for channel database generation, interactive testing, and minimal-configuration deployment. This work establishes semantic channel finding as a foundational capability for human-centric and agentic AI interfaces at large-scale facilities, providing both a systematic framework for architecture design and practical resources to enable adoption without building custom infrastructure from scratch.

channel finding↗
DOE OSTI2021

Exploring Fabrication of Ultra-low Absorption, Multilayer, Hafnium High Reflectors

Ultra-low absorption, high damage threshold coatings are critical for the advancement of the high power CW laser technologies, and in most cases, are a limiting factor for the output power. Since high power CW laser systems enable extremely high power irradiances, when the light is incident on an HR mirror, part of the energy is absorbed and converted into heat, which can have many detrimental side effects. The worst-case scenarios are optical distortion and laser-induced damage. These optics must operate reliably with irradiances of 100's kW/cm 2 to MW/cm 2 . The highest pulsed laser damage threshold high reflectors are consistently fabricated with hafnia material. However, hafnia is not the material of choice for high power CW laser systems because of very high absorption and scatter properties, factors of >100x higher than tantala-silica, due to its poly crystalline nature. This study focuses on CW laser use applications, where the coatings’ laser damage resistance is largely limited by the inherent absorption of the coating materials. The goal is to study the feasibility of utilizing a “composite” hafnium-silica and a “doped” hafnia-silica target materials to prohibit crystallization. The results from the study were extremely successful. Hafnia high reflectors coatings generated from this study exhibited one micron absorption values of approximately 1 ppm, which are the lowest reported values to date.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Optical damage considerations in the design of the matter in extreme condition upgrade (MEC-U) laser systems

The Matter in Extreme Conditions Upgrade (MEC-U) project is a major upgrade to the MEC instrument of the LINAC Coherent Light Source (LCLS) X-ray free electron laser (XFEL) user facility at SLAC National Accelerator Laboratory. Here, the envisioned MEC upgrade will significantly enhance the capabilities of the pump laser sources in current MEC experimental station, boosting the energy of the nanosecond shock driver from 100 J to the kJ level, and increasing the power and repetition rate of the short pulse laser from 25 TW at 5 Hz to 1 PW at 10 Hz rate. Building such high energy/power pump laser systems presents challenges to minimize and mitigate against laser-induced optical damage. Here, as part of the system design, we have identified the optics at high-risk to damage and we have designed the laser systems to mitigate against these damage risks to ensure sustained facility operation.

Coating↗
DOE OSTI2023

Diagnosing an IFE Power Plant

This white paper for the Basic Research Needs for Plasma Diagnostics workshop lists a selected set of measurements required for normal and off-normal operation of an Inertial Fusion Energy power plant. An Inertial Fusion Energy (IFE) power plant will require instruments that record how well it is performing and, more importantly, sufficient instruments to diagnose failures during routine operation. It is assumed in this white paper that operating specifications and tolerances have been established before the plant begins operation so that only a minimal set of instruments is required. A pilot plant (a DEMO) would require more instrumentation in order to set those requirements and tolerances. This white paper assumes a laser-based IFE plant that operates at up to 20 Hz. Two scenarios are considered below. One is for routine, nominal operation and the other is when an implosion fails to produce energy.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Leaky wave in high-power AlGaAs/InGaAs/GaAs semiconductor lasers

Lasers based on AlGaAs/InGaAs/GaAs heterostructures operating in the spectral range of 1.0 − 1.1 μm are investigated in order to optimise cladding layers. The effect of the thickness and composition of the cladding layers on the leakage of radiation from the laser waveguide is analysed. It is shown that for cladding thicknesses of 0.86 − 1.24 μm, it almost does not affect the output optical power. The effect of the crystal length and reflectivity of the laser mirrors on the leaky wave is demonstrated. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

High spatial resolution temperature profile measurements of solid-oxide fuel cells

Temperature gradients resulting from local electrochemical reactions, current distribution and geometry of gas flow channels in solid oxide fuel cells (SOFCs) create thermal stresses, localized thermophysical property gradients and uneven property evolution, contributing to SOFC degradation. This paper presents a new method to perform temperature measurements (up to 800°C) at high spatial resolutions to monitor the operation of SOFCs. Using femtosecond laser irradiation, distributed fiber sensors were hardened for high temperature environment applications. Distributed fiber sensors were embedded in interconnected plates using an additive manufacturing method to perform temperature measurements with 4-mm spatial resolution during the operation of a planar fuel cell. The measurement revealed the impact of various H 2 fuel concentrations and current loads have on temperature profiles of the SOFC tested. Temperature variation on the anode side was found to be less than 5°C, and 3°C on the cathode side. The measurements were compared to results from a multiphysics fuel cell performance model simulating similar conditions. These simulations predicted similar temperature gradients, indicating the experimental data obtained is reasonable. The model also predicts that the effect of the embedded sensor has on the local temperature will be minimal and that the gradient of temperature in the gas channels will be captured despite the separation between the sensor and the gas flow. Finally, the high spatial resolution data harnessed by these distributed fiber sensors provides experimental support for model-based design and optimization to improve the operational efficiency and longevity of solid oxide fuel cells and fuel cell assemblies.

25 ENERGY STORAGE↗
DOE OSTI2024

Effect of THz-bandwidth incoherent laser radiation on bulk damage in potassium dihydrogen phosphate crystals

Abstract The laser-damage performance characteristics of potassium dihydrogen phosphate (KDP) samples under exposure to a distinctive broadband incoherent laser pulse are investigated. A laser system providing such pulses is intended to explore improved energy-coupling efficiency on the target in direct-drive inertial confinement fusion experiments and provides incoherent bandwidths as large as 10 THz in a nanosecond pulse. A consequence of this bandwidth is very rapid fluctuations in intensity capable of reaching maxima much larger than the average intensity within the pulse. A custom damage-test station has been built to perform measurements with broadband incoherent pulses in order to determine what effect these fast and high-intensity oscillations have on laser damage. A set of experiments under different bandwidth and beam configurations shows the effect to be minimal when probing bulk damage in KDP. Modeling indicates this behavior is supported by long electron-relaxation times compared to the source-field fluctuations, following excitation of individual electrons in the conduction band. The results help better understand the laser-induced–damage mechanisms in KDP, and its ability to operate in broadband temporally incoherent high-energy lasers that may be particularly suitable for future laser-fusion energy systems.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Real-Time Elemental and Isotopic Measurements of Molten Salt Systems through Laser-Induced Breakdown Spectroscopy

Molten salt reactors are an emerging advanced nuclear reactor concept in which the fuel is dissolved into the working fluid in the form of a high-temperature molten salt. The complex, mobile, and corrosive nature of this fluid presents a fundamental challenge for analytical measurements. Tracking species throughout the reactor is important for ensuring proper operation. This article presents laser-induced breakdown spectroscopy (LIBS) used to monitor the elemental composition of a molten salt and corresponding hydrogen isotopic shifts in real-time. A NaNO 3 –KNO 3 eutectic salt was saturated with protium and deuterium gases, then the effluent aerosol stream formed using an argon sparging vessel was monitored with LIBS. This modular LIBS system permitted several spectrometers to be used simultaneously to capture high-resolution isotopic shifts and provide broadband elemental coverage. Further, the results exhibit how LIBS can be used to understand salt–gas chemical and physical interactions such as diffusion. Furthermore, LIBS’ broad elemental coverage can provide greater insight into the chemical reactions within the salt vessel such as the formation of water vapor by monitoring hydrogen and oxygen signatures simultaneously. Ultimately, this study demonstrates the analytical possibilities of LIBS for real-time monitoring of isotopes and elemental composition in molten salt systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Investigation of Superluminescent Diodes for Smart Lighting Systems. Final Report

The solid-state lighting ecosystem has evolved very rapidly over the last few years, with significant improvements in the technical performance of light-emitting diodes (LEDs) and the commoditization of LED-based lighting fixtures. As the performance of conventional lighting products begins to saturate, there is growing market interest in “Lighting as a Service” applications that will leverage advanced systems to impart new functionalities to lighting and improve energy efficiency, human health, and productivity. These “Smart Lighting” systems will include high-performance light sources, specialized sensors, and dynamic controls to deliver high quality, energy efficient, color tunable lighting with customized spatial light delivery and integrated visible light communication capability. To achieve these capabilities, smart lighting systems will place greater demands on the performance of light sources. Highly efficient sources with additional functionalities compared to conventional LEDs, such as small form factor, large modulation bandwidth, and spatially coherent output beams, will be required. While laser diodes have been proposed as potential sources for smart lighting systems, they also exhibit several properties that pose challenges, such as temporal coherence, extremely high spatial coherence, and ultra-narrow linewidths. To address these issues, we propose an investigation of an alternative device architecture known as a superluminescent diode (SLD). SLDs are similar in form to ridge laser diodes and share many of the same characteristics, such as stimulated emission operation, spatially coherent output, small form factor, and the potential for large modulation bandwidth. However, the operating principle for SLDs is distinct from laser diodes in that SLDs lack a strong cavity feedback mechanism, resulting in spatially coherent but temporally incoherent light output. Thus, SLDs may address the issues with laser diodes for lighting, while simultaneously maintaining some of the desirable characteristics of both laser diodes and LEDs. The objectives of this proposal are to design, grow, and fabricate blue (450 nm) SLDs on polar c-plane and nonpolar m-plane free-standing GaN substrates, and to evaluate their potential as sources in smart lighting systems through basic device characterization and detailed investigations of their efficiency droop and modulation bandwidth. The primary scientific aims of this work are to understand the fundamental role of optical gain in the superluminescent (non-lasing) regime on efficiency droop and modulation bandwidth in III-nitride emitters and to understand the effects of higher optical gain on SLD performance by comparing polar c-plane and nonpolar m-plane SLDs. The University of New Mexico (UNM) will collaborate with Sandia National Laboratories (SNL) and the Center for Integrated Nanotechnologies to design, fabricate, grow, and characterize the SLDs. UNM will perform the design and epitaxial growth, while SNL will focus on the fabrication and device characterization. The novelty of the proposed work includes the first comprehensive theoretical and experimental investigations of efficiency droop and the first investigation of modulation bandwidth in GaN-based emitters operating in the superluminescent regime. Moreover, the comparison of c-plane and m-plane SLDs will enable the first analysis of the effects of higher optical gain on the device performance. The development of high-performance GaN-based SLDs may enable efficiency gains and improved functionality in next-generation smart lighting systems.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2022

Considerations for a TeV collider based on dielectric laser accelerators

Particle acceleration in dielectric microstructures powered by infrared lasers, or "dielectric laser acceleration" (DLA), is a promising area of advanced accelerator research with the potential to enable more affordable and higher-gradient accelerators for energy frontier science and a variety of other applications. DLA leverages well-established industrial fabrication capabilities and the commercial availability of tabletop lasers to reduce cost, with axial accelerating fields in the GV/m range. Further, desirable luminosities would be obtained by operating with very low charge per bunch but at extremely high repetition rates. And as a consequence of its unique operating parameter regime, coupling of the laser to the accelerator can potentially be in the 50% range and with low beamstrahlung energy loss due at the interaction point, making DLA a promising approach for a future multi-TeV linear collider.

43 PARTICLE ACCELERATORS↗
DOE OSTI2024

Wavelength scaling and multicolor operation of a plasma-driven attosecond x-ray source via harmonic generation

The generation of high-power coherent soft x-ray pulses of sub-100 as duration and 10 nm wavelength using beams from a GeV energy plasma wakefield accelerator has been recently investigated in Emma []. As a future upgrade to this concept, this contribution investigates scaling to shorter x-ray wavelengths by cascading undulators tuned to higher harmonics of the fundamental. We present two simulation studies for plasma-driven attosecond harmonic generation schemes with final photon wavelengths of 2 and 0.40 nm. We demonstrate in these schemes that using undulators with retuned fundamental frequencies can produce GW-scale pulses of sub-nm radiation with tens of attosecond-scale pulse lengths, an order of magnitude shorter than current state-of-the-art attosecond x-ray free electron lasers (XFELs). This multipulse multicolor operation will be broadly applicable to attosecond pump-probe experiments. Published by the American Physical Society 2024

43 PARTICLE ACCELERATORS↗
DOE OSTI2022

Monitoring Xenon Capture in a Metal Organic Framework Using Laser-Induced Breakdown Spectroscopy

Molten salt reactor operation will necessitate circulation of a cover gas to remove certain evolved fission products and maintain an inert atmosphere. The cover gas leaving the reactor core is expected to contain both noble and non-noble gases, aerosols, volatile species, tritium, and radionuclides and their daughters. To remove these radioactive gases, it is necessary to develop a robust off-gas system, along with novel sensors to monitor the gas stream and the treatment system performance. In this study, a metal organic framework (MOF) was engineered for the capture of Xe, a major contributor to the off-gas source term. The engineered MOF column was tested with a laser-induced breakdown spectroscopy (LIBS) sensor for noble gas monitoring. The LIBS sensor was used to monitor breakthrough tests with various Xe, Kr, and Ar mixtures to determine the Xe selectivity of the MOF column. This study offers an initial demonstration of the feasibility of monitoring off-gas treatment systems using a LIBS sensor to aid in the development of new capture systems for molten salt reactors.

47 OTHER INSTRUMENTATION↗
DOE OSTI2026

Stable and tunable MeV $$\gamma$$-ray generation via dual-laser inverse Thomson scattering from a laser-plasma accelerator

Abstract Inverse Thomson scattering from laser-plasma accelerators offers a pathway to compact, tunable MeV $$\gamma$$ -ray sources for reduced-dose radiography and enhanced performance in nuclear resonance fluorescence (NRF)-based isotope identification. However, photon yield and spectral quality are often limited by constraints on interaction geometry and scatter-laser tunability. Here we demonstrate a MeV $$\gamma$$ -ray source based on a dual-laser inverse Thomson scattering configuration driven by a 100-TW laser-plasma accelerator. Electron beams tunable from 122 to 204 MeV with $$<5$$ mrad divergence and $$<1$$ mrad pointing stability generate $$\gamma$$ rays with peak energies from 276 keV to 1.2 MeV and yields up to $$2\times 10^{7}$$ photons per shot. By independently controlling the interaction position and the scatter-pulse duration, we experimentally match the scatter pulse to the walk-off-limited interaction length. Extending the scatter pulse to 200 fs increases photon production by approximately $$15\%$$ while maintaining operation in the linear Thomson regime, thereby preserving narrow spectral bandwidth and controlled radiation divergence. Radiographic characterization demonstrates MeV-level penetration and $$\approx 0.1$$ mm spatial resolution, while stable operation is sustained over multi-hour timescales across multiple days. These results show that interaction-length optimization provides a scalable strategy for improving photon yield, spectral control, and operational stability in compact laser-plasma-accelerator-driven $$\gamma$$ -ray sources.

Tsai, Hai-En↗
DOE OSTI2023

Electrical Analysis of Pulsed Laser Annealed Poly-Si: Ga/SiOx Passivating Contacts

In this contribution, we examine Ga hyper-doped poly-Si/SiOx contacts realized by pulsed laser melting (PLM). Here, we use Ga as a novel p-type dopant and B as a conventional dopant to induce non-equilibrium doping using an excimer laser. We perform simulations to visualize the maximum melt depth profiles within the poly-Si, with a goal of distributing dopants close to the tunneling oxide, but at the same time preserving the passivation. Hall measurements show that sheet resistance for B is lower than Ga due to its higher solid solubility limit in Si. After comparing the Hall active dopant concentration with the chemical concentration obtained by SIMS measurement, we show nearly 100% activation B activation reaching 10^21 cm-3, while only ~20% activation for Ga. Nevertheless, we achieve active doping concentrations of Ga in poly-Si six times higher than its solid solubility limit in Si (~10^19 cm-3). We compare our Hall mobilities with values in the literature for c-Si and show that B mobilities in laser-treated poly-Si are close to that of the literature value for B, while Ga mobilities are lower, possibly due to additional scattering channels within grain boundaries and deformed lattice. We also compare our results on PLM samples with conventional furnace annealed samples, and we show much higher percent activation and mobilities. Previously, we showed a low contact resistivity of 35.5 +/- 2.4 m..omega..cm2. Here, we further confirm this result by scanning spreading resistance microscopy and Kelvin force nanoprobe microscopy. We demonstrate that our poly-Si: Ga/nCz contact exhibits large drift and diffusion currents under normal cell operating voltage, which widens the laser processing window for a good metal/poly-Si/c-Si contact.

high-efficiency solar cells↗
DOE OSTI2022

Infrared Absorption Spectra of H2SO4, SO3, SO2, and H2O at 300C and 350C

Mid infrared absorption spectra of sulfuric acid (H2SO4), sulfur trioxide (SO3), sulfur dioxide (SO2), and water (H2O) were collected in a high temperature gas cell operating at either 300C or 350C. The spectra were collected using tunable external cavity quantum cascade lasers (ECQCLs) tuning, which were capable of operating over the wavelength range from approximately 7 microns to 9 microns, where H2SO4 and SO3 have their strongest absorption features. The spectra can be used as a library for developing gas sensors.

infrared absorption↗
DOE OSTI2021

Lasing Below 170 nm Using an Oscillator FEL

The short wavelength operation of free-electron laser (FEL) oscillators is limited by the availability of high-reflectivity, thermally stable, and radiation-resistant FEL mirrors in the VUV wavelength. We report our recent work to extend the shortest lasing wavelength of the oscillator FEL to 168.6 nm using a storage ring FEL. This progress has been made possible by developing a new FEL configuration with substantially reduced undulator harmonic radiation on the FEL mirror, a thermally stable FEL optical cavity, and a new type of high-reflectivity fluoride-based multilayer coating with a protective capping layer. Using these fluoride-based mirrors, we have demonstrated storage ring FEL lasing from 168.6 to 179.7 nm with excellent beam stability. Employing this VUV FEL in Compton scattering, we have produced the first 120 MeV gamma rays at the High Intensity Gamma-ray Source (HIGS). Furthermore, operating the HIGS in this new high-energy region will create many new opportunities for photonuclear physics research, in particular, the low-energy QCD research.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Study on ion current density of different species in laser produced plasma in a solenoid magnet

A solenoid magnetic field along the expanding laser-produced plasma is an essential technique of the laser ion source. The solenoid field can increase ion beam current at beam extraction point by a factor of 2 to over 100 by confining moving laser produced plasma in transverse direction. This technique is used everywhere from development lab to operational machine for user operation. However, the motion of ions in laser produced plasma is not fully understood. In this study, we experimentally investigated the motion of ions in a solenoid magnet (inner diameter 102 mm, coil length 1980 mm) for Al, Fe, and Ta targets. Using the following three conditions: full solenoid bore, a φ51 mm collimator on the solenoid axis, and a thin-wall φ51 mm tube at the bottom of the solenoid, we found that extracting ions at off-axis position (20~30 mm from the solenoid axis in this study) can enhance ion intensity by a factor of three or more. We continue to investigate ion motion in a solenoid field to develop better laser ion source design.

43 PARTICLE ACCELERATORS↗