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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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Replenishing liquid sheet targets to enable high-intensity high-repetition-rate laser–plasma interactions for ion-beam technology

We report on the development of a robust microfluidic nozzle capable of generating replenishing liquid sheet targets with sub-micron thickness at up to kHz repetition rates, a λ/20 surface flatness over areas of at least 100 μm 2 , and in-vacuum dimensions of 6 × 1.5 mm 2 . The platform was evaluated for stability under hundreds of 4.3 J laser shots at 0.5 Hz and 6 × 10 20 W/cm 2 peak intensity, delivered in burst mode, totaling 2.9 kJ on the target. The key metrics of the platform, including sheet characteristics, nozzle aperture morphology, and proton spectra, showed no measurable degradation in the performance of the liquid sheet platform following this experiment. Beyond its application to ion beam technology, we outline a pathway to further develop the capabilities of the platform into a high-repetition-rate plasma mirror.

depth profiling techniques↗
DOE OSTI2020

Radiofrequency synthesiser with an intrinsic instability of 5 × 10{sup −15} at the averaging time of 1 s based on a femtosecond erbium-doped fibre laser

A radio-optical synthesiser intended for operation in a radio-frequency master oscillator with an optical He – Ne/CH{sub 4} frequency standard (λ = 3.39 μm) is developed on the basis of a femtosecond erbium-doped fibre laser. The synthesiser generates equidistant harmonics in the frequency range of 1 – 10 GHz with stability determined by the optical frequency standard. A stable supercontinuum spectrum is formed in the range around 1.06 μm, which provides stable 24-hour operation of the synthesiser and is important for practical applications in off-laboratory conditions. A direct comparison of the output frequencies of two synthesisers shows that the up-grade of the fibre laser and detection system of femtosecond pulses results in the synthesiser intrinsic instability of 5 × 10{sup −15} at the averaging time of 1 s. Such a value is by an order of magnitude less than that obtained in our earlier works. (laser frequency standards)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Solid-state laser refrigeration of a composite semiconductor Yb:YLiF 4 optomechanical resonator

Photothermal heating represents a major constraint that limits the performance of many nanoscale optoelectronic and optomechanical devices including nanolasers, quantum optomechanical resonators, and integrated photonic circuits. Here, we demonstrate the direct laser refrigeration of a semiconductor optomechanical resonator >20 K below room temperature based on the emission of upconverted, anti-Stokes photoluminescence of trivalent ytterbium ions doped within a yttrium-lithium-fluoride (YLF) host crystal. Optically-refrigerating the lattice of a dielectric resonator has the potential to impact several fields including scanning probe microscopy, the sensing of weak forces, the measurement of atomic masses, and the development of radiation-balanced solid-state lasers. In addition, optically refrigerated resonators may be used in the future as a promising starting point to perform motional cooling for exploration of quantum effects at mesoscopic length scales, temperature control within integrated photonic devices, and solid-state laser refrigeration of quantum materials.

42 ENGINEERING↗
DOE OSTI2023

350 mJ electro-optically Q-switched 2.79 µm Cr:Er:YSGG MOPA

We report on developing three flashlamp-pumped electro-optically Q-switched Cr:Er:YSGG lasers with the Q-switch based on a La 3 Ga 5 SiO 14 crystal. The “short” laser cavity was optimized for high peak power applications. In this cavity, 300 mJ output energy in 15 ns pulses at a 3 Hz repetition rate was demonstrated with pump energy below 52 J. However, several applications, such as Fe:ZnSe pumping in a gain-switched regime, require longer (∼ 100 ns) pump pulse duration. We developed a 2.9 m long laser cavity that delivers 190 mJ of output energy in 85 ns pulses for these applications. We also demonstrated the Cr:Er:YSGG MOPA system producing 350 mJ output energy at 90 ns pulse duration and 47.5 J of pumping, corresponding to an amplification factor of 3.

47 OTHER INSTRUMENTATION↗
DOE OSTI2024

Development of a high performance MagLIF target platform using high aspect ratio coated liners and low-mix laser preheat

We report on a series of Magnetized Liner Inertial Fusion (MagLIF) experiments conducted on the Z pulsed power facility that utilized high aspect ratio (ratio of outer radius to wall thickness) liners with dielectric coatings and low-mix laser preheat configurations. The liners consisted of an aspect ratio of 10.6 beryllium tube coated with 75 μm of epoxy on the outside that have been shown to maintain a better implosion stability than uncoated beryllium and have demonstrated consistent stagnation performances in previous experiments [Ampleford et al., Phys. Plasmas 31, 022703 (2024)]. Two-dimensional HYDRA simulations were used to design three different “co-injection” laser configurations, whereby a second laser is used to provide an early prepulse before the main pulse, to reduce LEH foil mix while increasing the fuel density and coupled energy. The laser preheat energy for each configuration was constrained using dedicated laser experiments before being applied to the integrated MagLIF experiments on Z. The DD neutron yield for experiments using co-injection preheat configurations is found to increase with the specific preheat energy in line with simulations. The highest neutron yield achieved in this study of 1.1 × 10 13 matches the highest reported in a MagLIF experiment to date and is a factor 3.5 times higher than similar experiments using preheat with no phase plate smoothing. We attempt to assess the effects of mix and morphology to explain the improved performance; however, neither factor is found to be conclusive within the uncertainty of the measurements.

Harvey-Thompson, A. J.↗
DOE OSTI2024

Development of a broadband reflective phase retarder to generate circularly polarized light for MTW-OPAL and multipetawatt lasers

Here, our research focuses on designing metallic coatings to create broadband all-reflective phase retarders that generate circularly polarized (CP) light for the MTW-OPAL Laser System while ensuring the desired polarization state on the target. This all-reflective phase retarder can function as a phase retarder when used in an out-of-plane configuration, whereas it acts as a normal mirror set in an in-plane configuration. If the polarization of the beam is not purely s- or p-polarized, however, mirrors will in general introduce retardance, and therefore compensators or polarization-independent mirror pairs are needed to ensure the desired polarization at the target plane.

47 OTHER INSTRUMENTATION↗
DOE OSTI2022

Quarterly Management Document – FY22, 3rd Quarter, Multi-pass Hybrid Laser Arc Welding of Alloy 740H

During the 3rd quarter of FY22, progress was made on modeling and simulation of deep penetration laser welding of Alloy 740H. Advances in the modeling of residual stress development arising from the calculated temperature field of the solidifying weld pool were made to understand the development of solidification cracking. Additionally, preliminary modeling of the temperature field within the weld pool of a wobbling laser heat source was performed. The maximum temperature of the weld pool was found to vary with time. These result will allow modeling of deep penetration laser welding using a wobbling laser to mitigate weld defects and cracking. Also, additional characterization of hybrid laser arc welds indicated that these welds were not defect-free as originally thought and the current HLA welds would not be acceptable under criteria outlined in the ASME Boiler and Pressure Vessel Code, Section IX. Therefore, additional welding trails with variation of the welding parameters and HLA welding configurations are required to produce welds acceptable under the Section IX criteria. It was shown that considerable reduction of HLAW defects had been achieved with each successive welding campaign. Therefore additional variation of HLAW parameters may still yield the desired defect-free welds, however, options for alternate HLAW configurations as well as plate preheating are outlined as contingency plans to obtain suitable welds. These additional (unplanned) HLAW trial may prevent subsequent milestones from being achieved within the original budget.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Studies of High Energy Density Discharge and Laser-Driven Deflagrating Plasma Stagnations

The goal of this proposal is to develop an understanding of the thermalization and mixing of high energy density (HED) interpenetrating and stagnating plasma deflagrations on two different platforms. The first is opposing gas-fed Z-pinch plasma expansions in a facility at Stanford University. The second is the convergence of multiple deflagration fronts generated by inverted corona laser ablations through experiments carried out by the P.I. as part of a larger team at the University of Rochester Laboratory for Laser Energetics. The link between the two platforms is the role played by kinetic effects that impact mixing and the conversion of directed to thermal energy. Such kinetic effects are important because of the relatively high temperatures despite high plasma densities.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Pulse Radiolysis Study of Radiation Effect on Molten Salt

The molten salt reactor concept, where nuclear fuel is dissolved in a molten salt that also serves as the heat transfer fluid, is a leading candidate for next generation nuclear reactors. This necessitates a thorough understanding of radiation effects on molten salt media to support the design, development, and deployment of such reactors. Early, pioneering pulse radiolysis molten salt experiments observed key primary radiolysis products such as the solvated electron (esolv?) and dichloride radical anion (Cl2??), but left many fundamental mechanistic and reactivity questions unanswered. Here we report on the reaction kinetics of esolv? and Cl2?? in molten LiCl-KCl eutectic salt doped with Zn2+ ion, using electron pulse radiolysis to observe the transient behavior from nanosecond to microsecond time scales. Experiments were performed at the BNL Laser-Electron Accelerator Facility using a recently-developed high-temperature sample holder. Prompt formation of esolv? and Cl2?? are observed; esolv? decays within hundreds of nanoseconds while Cl2?? decays more slowly by second-order kinetics, more likely by cross-recombination rather than disproportionation. This work was supported as part of the Molten Salts in Extreme Environments Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science.

38 - RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCL↗
DOE OSTI2025

Pulsed laser deposition assisted epitaxial growth of cesium telluride photocathodes for high brightness electron sources

The development of high-brightness electron sources is critical to state-of-the-art electron accelerator applications like X-ray free electron laser (XFEL) and ultra-fast electron microscopy. Cesium telluride is chosen as the electron source material for multiple cutting-edge XFEL facilities worldwide. This manuscript presents the first demonstration of the growth of highly crystalized and epitaxial cesium telluride thin films on 4H-SiC and graphene/4H-SiC substrates with ultrasmooth film surfaces. The ordering of the film was characterized by in situ reflection high energy electron diffraction and multiple X-ray diagnostics. The results of the quantum efficiency performance for epitaxial cesium telluride photocathodes are also reported.

43 PARTICLE ACCELERATORS↗
DOE OSTI2025

Automated and highly parallelized Bayesian optimization scheme for direct drive fusion experiments on OMEGA

Finding the optimal implosion design on existing experimental facilities for inertial confinement fusion requires an exhaustive search of the vast design parameter space. This is infeasible both with experiments and with simulations. Consequently, a large fraction of the experimentally realizable design space remains unexplored, and new design schemes are challenging to optimize in a reasonable time frame. On the OMEGA laser facility, predictive machine learning models have been developed to accurately forecast the result of an experiment using only inexpensive simulations and the large dataset of prior experimental data. However, the full design space remains vast enough to be unassailable with simple optimization techniques. Here we develop an automated and optimally parallel Bayesian optimization algorithm that can entirely optimize the target and pulse shape of a direct-drive ICF implosion under a given design paradigm. We use this algorithm to find a markedly improved design for the performance implosions on OMEGA that is predicted to hydroequivalently scale to ignition at 2.15 MJ.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Indirect Liftoff Mechanism for High‐Throughput, Single‐Source Laser Scribing for Perovskite Solar Modules

A high‐throughput, single‐source laser scribing method exploiting a transparent conducting oxide (TCO) indirect liftoff mechanism is developed to produce serially interconnected perovskite solar modules. The TCO‐based indirect liftoff mechanism relies solely on laser absorption in the front transparent electrode material reducing thermal damage to the overlying layers and allowing for fast scribing speeds with low‐cost μs‐pulse duration fiber laser systems. Minimal resistive power losses are observed with the method compared to conventional ablative laser scribes, maintaining the power conversion efficiencies of small‐area devices (≈0.2 cm 2 ) across significantly larger deposition areas (≈1 cm 2 ). Finally, demonstrating > 3 m s −1 processing speeds, TCO‐based liftoff provides the highest throughput laser scribing method for thin‐film photovoltaic devices produced on glass/TCO substrates, capable of processing large‐area perovskite solar modules at a manufacturing scale.

14 SOLAR ENERGY↗
DOE OSTI2024

Laser-Doppler Anemometry Measurements of Turbulent Swirling Wakes

This study considers the development and evolution of the swirling turbulent wake and their link to the turbulence present in the wake. A wake generator produces swirling wakes with a minimum of artifacts that would complicate the flow. Four swirling wakes have been studied with swirl numbers ranging from 0.19 to 0.37, and the results are compared to those of a nonswirling wake. Two-component laser-Doppler anemometry has been used to measure mean and turbulence quantities in the wake, and the uncertainty of these quantities has been determined. Careful alignment of the laser-Doppler anemometry system and large numbers of independent samples were used to obtain second-order turbulence statistics with low uncertainty. The results indicate that swirl strength impacts wake behavior, and changes in the behavior are linked to modifications in the turbulence. Faster wake width growth and centerline velocity deficit decay have been observed for wakes with higher swirl strength. The results indicate that a minimum swirl level is required to significantly impact wake behavior, and, at some level of swirl, the enhanced wake evolution observed saturates. For the conditions tested, the swirl number that enhances wake diffusion before saturation has been determined to lie between 0.21 and 0.37.

Engineering↗
DOE OSTI2021

Multiplexable intrinsic Fabry-Pérot interferometers inscribed by femtosecond laser for vibration measurement in high temperature environments

This article reports fabrication technique and demodulation algorithm developments to use multiplexable intrinsic Fabry-Pérot interferometer (IFPI) fiber sensor array for distributed vibration measurements at high temperatures. Using femtosecond laser direct writing scheme, IFPI array were fabricated through laser-induced Type II scattering points in single mode fiber cores. Reflection spectra of IFPI array were demodulated in real-time using modified Bunemen frequency analysis. The demodulation algorithm, which was implemented using a photodetector-array spectrometer, achieves 64-nε dynamic strain resolution at 1-kHz spectral acquisition rate and 2-kHz maximum vibration bandwidth. Performance and stabilities of IFPI sensor array were characterized from room temperatures to 800 °C. The static strain resolution was 0.6 με and the minimum detectable dynamic strain amplitude was 23 nε/√Hz at 800 °C. The multiplex performance was also tested by measuring dynamic strain in time domain through six IFPI sensor array fabricated in one fiber. This paper presents an integrated and low-cost sensing solution to perform distributed vibration measurements in harsh environments.

42 ENGINEERING↗
DOE OSTI2025

Multi-physics melt pool modeling and process optimization for laser direct energy deposition of Nb-based refractory C103: Defect formation, geometric precision, and process mapping

Recent developments in additive manufacturing (AM) technology have reignited interest in the fabrication of the Nb-based refractory C103 alloy offering solutions to the challenges posed by traditional manufacturing methods. However, the limited numerical and experimental studies on laser direct energy deposition (DED) of C103 have hindered the understanding of the relationships between process parameters and build quality. This has made it challenging to consistently produce parts with the desired quality and microstructure suitable for critical applications. In this study, we focus on optimizing the laser DED process for C103 by employing a hybrid approach that combines experimental techniques and computational fluid dynamics (CFD). This approach facilitates the development of process maps for defect detection and geometric precision. To achieve this, multi-layer C103 samples were fabricated using laser DED under various process parameters, enabling the creation of a process map for defect detection. Additionally, a multi-physics, multiphase simulation framework was developed within a high-performance computing (HPC) environment to establish process maps for geometric precision. Using these process maps, printability windows were identified for achieving both the desired geometric accuracy and defect-free prints. It was observed that prints with a power-to-velocity (P/V) ratio close to unity resulted in defect-free outcomes. This study provides a foundation for reducing design lead time and rejected parts, ultimately optimizing the laser DED process for C103.

Defect formation and geometric precision↗
DOE OSTI2021

A laser inverse Compton scattering diagnostic to study runaway electron dynamics during tokamak disruptions

The goal is to design a new diagnostic based on laser inverse Compton scattering (LICS) to study the dynamics of runaway electron formation and their subsequent loss during triggered disruptions in DIII-D. It is known that better measurements of the runaway electron population, throughout the evolution of a disruption, is critical for mitigating the impact of energetic electron beams especially in high plasma current discharges such as those in reactor relevant burning plasmas. The goal of the LICS approach being designed for DIII-D is to measure the timeresolved spatial profile and energy distribution of the runaway electrons while they are in the core of the tokamak plasma. During the last year, a code was developed to simulate the signals from a new laser scattering diagnostic for DIII-D, which will measure the relativistic electron population expected in DIII-D after disruptions triggered by argon pellet injection.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Compact single-shot electro-optic detection system for THz pulses with femtosecond time resolution at MHz repetition rates

Electro-optical detection has proven to be a valuable technique to study temporal profiles of THz pulses with pulse durations down to femtoseconds. As the Coulomb field around a relativistic electron bunch resembles the current profile, electro-optical detection can be exploited for non-invasive bunch length measurements at accelerators. We have developed a very compact and robust electro-optical detection system based on spectral decoding for single-shot longitudinal bunch profile monitoring at the European X-ray Free Electron Laser (XFEL) for electron bunch lengths down to 200 fs (rms). Apart from the GaP crystal and the corresponding laser optics at the electron beamline, all components are housed in 19 in. chassis for rack mount and remote operation inside the accelerator tunnel. An advanced laser synchronization scheme based on radio-frequency down-conversion has been developed for locking a custom-made Yb-fiber laser to the radio-frequency of the European XFEL accelerator. In order to cope with the high bunch repetition rate of the superconducting accelerator, a novel linear array detector has been employed for spectral measurements of the Yb-fiber laser pulses at frame rates of up to 2.26 MHz. In this paper, we describe all sub-systems of the electro-optical detection system as well as the measurement procedure in detail and discuss the first measurement results of longitudinal bunch profiles of around 400 fs (rms) with an arrival-time jitter of 35 fs (rms).

47 OTHER INSTRUMENTATION↗