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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Plasmonics-enhanced photoconductive terahertz detector pumped by Ytterbium-doped fiber laser

We present a photoconductive terahertz detector operating at the 1 µm wavelength range at which high-power and compact Ytterbium-doped femtosecond fiber lasers are available. The detector utilizes an array of plasmonic nanoantennas to provide sub-picosecond transit time for the majority of photo-generated carriers to enable high-sensitivity terahertz detection without using a short-carrier-lifetime substrate. By using a high-mobility semiconductor substrate and preventing photocarrier recombination, the presented detector offers significantly higher sensitivity levels compared with previously demonstrated broadband photoconductive terahertz detectors operating at the 1 µm wavelength range. We demonstrate pulsed terahertz detection over a 4 THz bandwidth with a record-high signal-to-noise ratio of 95 dB at an average terahertz radiation power of 6.8 µW, when using an optical pump power of 30 mW.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

An extended Vlasov–Fokker–Planck approach for kinetic simulations of laser plasmas

Vlasov–Fokker–Planck simulation codes occupy an important niche in modeling laser-produced plasmas, since they are well suited to studying the effect of collisions on electron kinetic phenomena, especially energy transport. One of the most important elements of energy transport is the absorption of laser light by the plasma; however, simulating this in detail requires resolving oscillations of the laser light, whose characteristic timescale is orders of magnitude shorter than the simulation time needed to study transport physics. For this reason, most Vlasov–Fokker–Planck codes used to study electron transport in laser plasmas rely on simplified models of the laser–plasma coupling. Their underlying assumptions nominally preclude their use for modeling laser light having short-scale structure in space or time, such as broadband lasers. In this work, we derive a more general computational framework suitable for arbitrarily structured laser fields. Furthermore, our approach is based on an extended set of Vlasov–Fokker–Planck equations that separately solve for the low- and high-frequency plasma response. We implement these extended Vlasov–Fokker–Planck equations in the spherical harmonic code K2 and demonstrate the performance of the method on several laser absorption test problems, with particular attention to the judicious selection of time steps, time integrators, and spherical harmonic truncation, according to the intensity and spectrum of the laser light under consideration. Comparison with the widely used Langdon absorption operator shows the Langdon operator performs remarkably well for predicting laser heating in the simple cases considered here, even in situations that would seem to violate its underlying assumptions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Three-colour digital holographic microscopy based on a Mach – Zender interferometer and a solid-state RGB laser

We have developed a facility for recording colour digital holograms involving a Mach – Zender interferometer and a pulsed solid-state RGB laser, which radiates simultaneously at three wavelengths: 451, 532, and 634 nm. These wavelengths are obtained in the conversion of the radiation of a pulsed Nd{sup 3+} : YAG laser (1064 nm), which operates in the regime of intracavity parametric oscillation at a wavelength of 1570 nm, with the subsequent conversion of its frequencies to the red, green, and blue spectral regions in nonlinear KTP-crystal elements. The combination of this three-wavelength pulsed light source with the Mach – Zender interferometer provides the simultaneous recording of three spectral digital holograms with one matrix RGB radiation detector. Pulsed three-colour digital holography shows promise for the analysis of fast processes and rapidly varying colour phase objects. (paper)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2023

Phase Locking of a THz QC-VECSEL to a Microwave Reference

We report high-resolution frequency study and phase locking have been performed on a terahertz (THz) quantum-cascade vertical-external-cavity surface-emitting laser (QC-VECSEL) operating around 2.5 THz. A subharmonic diode mixer is used to down convert the THz signal to a 100 MHz intermediate frequency that is phase locked to a stable 100 MHz microwave reference. Between 90% and 95% of the QC-VECSEL signal is locked within 2 Hz of the multiplied RF reference, and amplitude fluctuations on the order of 1%–10% are observed, depending on the bias point of the QC-VECSEL. The bandwidth of the locking loop is ~1 MHz. Many noise peaks in the IF signal are observed, likely corresponding to mechanical resonances in the 10 Hz–10 kHz. These peaks are generally -30 to -60 dB below the main tone and are below the phase noise level of the multiplied RF reference that ultimately limits the phase noise of the locked QC-VECSEL.

42 ENGINEERING↗
DOE OSTI2021

Specification of EBR-II Laser Profilometry Data

All laser profilometry data stored in FIPD were originally measured using the element laser profilometer system in HFEF/N. The irradiated fuel elements or pins were scanned by a laser beam to measure the outer diameter with position mapping of the spacer wire. The normal operation and data collection were performed automatically with HFEF/N Data Acquisition and Process Control System (DAPCS). With the digital control system, measured laser profilometry data were recorded in digital form on magnetic tapes, different from the analog contact profilometry data recorded by strip-chart record sheets. Two documents contained most of the important details about laser profilometry measurements. The first one is the operational manual of the laser profilometer (title: Element laser profilometer (ELP) operation and maintenance manual, HFEF/N OMM 4329, DOC. NO. W0171-0149-ES-01). This manual provides: (1) description of laser profilometer including the functions of each component (transceiver, retroreflector, clamping guide, shielding enclosure, electronic controller, etc.); (2) step-by-step guidance for calibrations, operations and measurements; and (3) maintenance procedures and other details of the element laser profilometer. Since first issued on 12/1/1986, several revisions/changes of the manual were developed to update the measurement accuracies and other factors for the laser profilometer system. The second document is a publicly accessible conference article titled “the element laser profilometer system in HFEF/N.” This article summarizes important functions and parameters of the laser profilometer. The range of measurements and the uncertainties reported in the article were consistent with the values reported in the operational manual.

42 ENGINEERING↗
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 OSTI2025

femto-PIXAR: a self-supervised neural network method for reconstructing femtosecond X-ray free electron laser pulses

X-ray Free Electron Lasers (X-FELs) operate in a wide range of lasing configurations for a broad variety of scientific applications at ultrafast time-scales such as structural biology, materials science, and atomic and molecular physics. Shot-by-shot characterization of the X-FEL pulses is crucial for analysis of many experiments as well as tuning the X-FEL performance. However, for the weak pulses found in advanced configurations, e.g. those needed for coherent, two-pulse studies of quantum materials, there is no current method for reliably resolving pulse profiles. Here we show that a physics-based U-net model can reconstruct the individual pulse power profiles for sub-picosecond pulse separation without the need for simulations. Using experimental data from weak X-FEL pulse pairs, we demonstrate we can learn the pulse characteristics on a shot-by-shot basis when conventional methods fail.

43 PARTICLE ACCELERATORS↗
DOE OSTI2020

Physics and applications of quantum dot lasers for silicon photonics

Abstract Photonic integrated circuits (PICs) have enabled numerous high performance, energy efficient, and compact technologies for optical communications, sensing, and metrology. One of the biggest challenges in scaling PICs comes from the parasitic reflections that feed light back into the laser source. These reflections increase noise and may cause laser destabilization. To avoid parasitic reflections, expensive and bulky optical isolators have been placed between the laser and the rest of the PIC leading to large increases in device footprint for on-chip integration schemes and significant increases in packaging complexity and cost for lasers co-packaged with passive PICs. This review article reports new findings on epitaxial quantum dot lasers on silicon and studies both theoretically and experimentally the connection between the material properties and the ultra-low reflection sensitivity that is achieved. Our results show that such quantum dot lasers on silicon exhibit much lower linewidth enhancement factors than any quantum well lasers. Together with the large damping factor, we show that the quantum dot gain medium is fundamentally dependent on dot uniformity, but through careful optimization, even epitaxial lasers on silicon can operate without an optical isolator, which is of paramount importance for the future high-speed silicon photonic systems.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Laser calibration system at ProtoDUNE-HD

The Deep Underground Neutrino Experiment (DUNE) is a full experiment consisting of multiple detectors separated by a near and far site. DUNE will study long-baseline neutrino oscillations, which will provide insight into CP-violation, neutrino mass ordering, and the matter/antimatter asymmetry. Additionally, DUNE will search for nucleon decay and observe neutrinos from supernovae. DUNE relies on liquid argon time projection chambers (LAr TPCs), an excellent technology for tracking particles and reconstructing their interactions with high precision. To achieve its goals, DUNE is supported by the ProtoDUNE experiments at CERN, which serve as large-scale prototypes to validate detector technologies and calibration systems. The precise calibration of the electric field within the detector is vital for accurate 3D reconstruction of particle tracks, particularly in maintaining the consistency of charge measurements along the drift path. This work presents the development and implementation of a laser calibration system designed for ProtoDUNE-II. This poster involved the physical installation and commissioning of the laser system. The commissioning process included extensive testing to ensure alignment and operational efficiency, such as rotating the laser to observe behavior of tracks. The groundwork established during these steps is crucial for future data analysis, aiming to measure the electron lifetime (in the active volume) and map the electric field inside the detector with high precision.

Campanelli, Wallison [LIP]↗
DOE OSTI2022

Survey of spatio-temporal couplings throughout high-power ultrashort lasers

The investigation of spatio-temporal couplings (STCs) of broadband light beams is becoming a key topic for the optimization as well as applications of ultrashort laser systems. This calls for accurate measurements of STCs. Yet, it is only recently that such complete spatio-temporal or spatio-spectral characterization has become possible, and it has so far mostly been implemented at the output of the laser systems, where experiments take place. In this survey, we present for the first time STC measurements at different stages of a collection of high-power ultrashort laser systems, all based on the chirped-pulse amplification (CPA) technique, but with very different output characteristics. This measurement campaign reveals spatio-temporal effects with various sources, and motivates the expanded use of STC characterization throughout CPA laser chains, as well as in a wider range of types of ultrafast laser systems. In this way knowledge will be gained not only about potential defects, but also about the fundamental dynamics and operating regimes of advanced ultrashort laser systems.

Jeandet, Antoine (ORCID:0000000345493067)↗
DOE OSTI2021

Tunable quantum-cascade VECSEL operating at 19 THz

We report a terahertz quantum-cascade vertical-external-cavity surface-emitting laser (QC-VECSEL) emitting around 1.9 THz with up to 10% continuous fractional frequency tuning of a single laser mode. The device shows lasing operation in pulsed mode up to 102 K in a high-quality beam, with the maximum output power of 37 mW and slope efficiency of 295 mW/A at 77 K. Challenges for up-scaling the operating wavelength in QC metasurface VECSELs are identified.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2024

Repair strategy for fused silica wedged focus lens with high-density filamentary damage

The National Ignition Facility (NIF) is intentionally operated with the final fused silica glass (SiO2) optics exposed to fluences and intensities with the potential to induce damage that will grow with additional laser exposure. Therefore, the NIF operates a recycle loop to refurbish final optics by mitigating any initiated surface damage to arrest its growth. However, the morphology of filamentary damage, caused by local self-focusing in the bulk of a silica optic, adds complexity to optics mitigation and provides a limitation to optic reusability. Here, we evaluate techniques for mitigating isolated and clustered filamentary damage. Optical microscopy before and after installation on NIF was used to determine the efficacy of filamentary mitigation after a series of high fluence and intensity laser exposures. The challenges and success rate of the methods are compared for various filamentary damage mitigation strategies.

National Ignition Facility↗
DOE OSTI2023

Performance characterization of freeform finished surfaces of potassium dihydrogen phosphate using fluid jet polishing with a nonaqueous slurry

Abstract Potassium dihydrogen phosphate (KDP) and its deuterated analog (DKDP) are unique nonlinear optical materials for high power laser systems. They are used widely for frequency conversion and polarization control by virtue of the ability to grow optical-quality crystals at apertures suitable for fusion-class laser systems. Existing methods for freeform figuring of KDP/DKDP optics do not produce surfaces with sufficient laser-induced–damage thresholds (LIDT’s) for operation in the ultraviolet portion of high-peak-power laser systems. In this work, we investigate fluid jet polishing (FJP) using a nonaqueous slurry as a sub-aperture finishing method for producing freeform KDP surfaces. This method was used to selectively polish surface areas to different depths on the same substrate with removals ranging from 0.16 μm to 5.13 μm. The finished surfaces demonstrated a slight increase in roughness as the removal depth increased along with a small number of fracture pits. Laser damage testing with 351 nm, 1 ns pulses demonstrated excellent surface damage thresholds, with the highest values in areas devoid of fracture pits. This work demonstrates, for the first time, a method that enables fabrication of a waveplate that provides tailored polarization randomization that can be scaled to meter-sized optics. Furthermore, this method is based on FJP technology that incorporates a nonaqueous slurry specially designed for use with KDP. This novel nonaqueous FJP process can be also used for figuring other types of materials that exhibit similar challenging inherent properties such as softness, brittleness, water-solubility, and temperature sensitivity.

36 MATERIALS SCIENCE↗
DOE OSTI2021

High-power narrow spectrum GaSb-based DBR lasers emitting near 2.1 µm

Stable high-power narrow-linewidth operation of the 2.05–2.1 µm GaSb-based diode lasers was achieved by utilizing the sixth-order surface-etched distributed Bragg reflector (DBR) mirrors. The DBR multimode devices with 100 µm wide ridge waveguides generated ~850 mW in the continuous wave (CW) regime at 20°C. The device CW output power was limited by thermal rollover. The laser emission spectrum was defined by Bragg reflector reflectivity at all operating currents in a wide temperature range. Finally, the devices operated at DBR line with detuning from gain peak exceeding 10 meV.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

Methods and apparatus for comprehensive characterization of performance attributes and damage thresholds of ultrafast laser optics

It is presently well understood that the operational performance limits of optics are determined by three fundamental attributes: the initiation of laser-induced damage, the growth of damage sites, and the transient (nondamaging) modification of optical parameters. The comprehensive characterization of the performance limitations of ultrafast optics requires consideration of all three fundamental attributes. Here, the vast majority of literature to date, however, has focused primarily on damage-initiation and testing systems that are largely focused on determining the damage-initiation threshold under single- and multipulse excitation. In this work, we discuss a testing apparatus that was designed to offer the capability to adequately characterize all three of these performance attributes under femtosecond, near-infrared laser irradiation. Key aspects of methodology are discussed, including high-dynamic-range energy control, variable beam size, wavelength tunability, B-integral management, and functional performance characterization to explore the true operational limits of the components. Example results for a metal-dielectric mirror demonstrate the test station’s operation.

42 ENGINEERING↗
DOE OSTI2021

Measurements of dynamic surface changes by digital holography for in situ plasma erosion applications

There are currently few viable diagnostic techniques for in situ measurement of plasma facing component erosion. Digital holography is intended to fill this gap. Progress on the development of single and dual CO 2 laser digital holography diagnostics for in situ plasma facing component erosion is discussed. The dual laser mode’s synthetic wavelength allows the measurable range to be expanded by a factor of ~400 compared to single laser digital holography. This allows the diagnostic to measure surface height changes of up to 4.5 μm in single laser mode and up to 2 mm in dual laser mode. Results include ex situ measurements of plasma eroded targets and also dynamic measurements of nm and μm scale motion of a target mounted on a precision translation stage. Dynamic measurements have successfully been made with the system operating in both single and dual laser modes, from ~50 nm to ~4 μm in single laser mode and up to ~400 μm in dual laser mode (limited only by the stage speed and camera acquisition duration). These results demonstrate the feasibility of using digital holography to characterize plasma facing component erosion dynamically, i.e., during plasma exposure. Results of proof-of-principle in situ digital holographic measurements of targets exposed to an electrothermal arc plasma source are presented.

Smith, Cary↗
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↗