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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
NASA NTRS2024

Uncertainty Budget for Detector-Based Absolute Radiometric Calibration With GLAMR

The accuracy of the absolute radiometric calibration (RadCal) for remote sensing instruments is essential to their wide range of applications. The uncertainty associated to the traditional source-based RadCal method is assessed at a 2% (k=1) or higher level for radiance measurement. To further improve the accuracy to meet the demands of climate studies, a detector-based approach using tunable lasers as a light source has been devised. The Goddard Laser for Absolute Measurement of Radiance, known as the GLAMR system, is a notable example of the incorporation of such technology. Using transfer radiometers calibrated at NIST as calibration standards, the absolute spectral response (ASR) function of a remote sensing instrument is measured with its uncertainty traceable to the International System of Units. This paper presents a comprehensive uncertainty analysis of the detector-based absolute RadCal using the GLAMR system. It identifies and examines uncertainty sources during the GLAMR RadCal test, including those from the GLAMR system, the testing configuration, and data processing methodologies. Analysis is carried out to quantify the contribution of each source and emphasize the most influential factors. It is shown that the calibration uncertainty of GLAMR RadCal can be better than 0.3% (k=1) in the wavelength range of 350-950 nm and 0.6% (k=1) between 950-2300 nm, with the exception of regions with strong water absorption. In addition, recommendations are made to refine the calibration process to further reduce the uncertainty.

Zhipeng Wang↗
NASA NTRS1975

Investigation of laser dynamics, modulation and control by means of intra-cavity time varying perturbation

The generation of tunable visible, infrared, and ultraviolet light is examined, along with the control of this light by means of novel mode-locking and modulation techniques. Transient mode-locking of the Nd:YAG laser and generation of short tunable pulses in the visible and the alkali metal inert gas excimer laser systems were investigated. Techniques for frequency conversion of high power and high energy laser radiation are discussed, along with high average power blue and UV laser light sources.

Harris, S. E.↗
NASA NTRS2023

Orion Cabin Lighting System: Filter Workaround for Maintaining Crew Circadian Entrainment

Introduction: Suboptimal crew circadian entrainment (CCE) is common and results in cumulative fatigue and reduced cognitive function. This may promote use of psychostimulants and hypnotics. The Orion Cabin Lighting System (OCLS) consists of 15 dimmable lamps circuited to several zones. The OCLS monochromatic white lamp design is insufficient for maintaining CCE. While blue light (480-nm) elicits peak wake-cycle response, it is a powerful disruptor of CCE. We propose OCLS lamp filters (OLFs) as a workaround for maintaining CCE. Methods: Preliminary OLFs testing utilized a tunable-white LED to serve as a baseline lamp in the NASA Lighting Lab’s controlled environment (prototype OCLS lamps were unavailable). Illuminance and spectral irradiances were measured with the NASA Lighting Lab’s spectroradiometer. ConOps is proposed for OLFs. Results: OLFs markedly attenuated 480-nm light and illumination with minimal mass/volume requirements. ConOps includes in-flight deployment of OLFs and reducing OCLS lamp intensity prior to bedtime. Pros: minimal mass/volume, no added power, and a simplistic design. Cons: manual twice-daily articulation of OLFs, undetermined frangibility/flammability/off-gassing and effects on thermal regulation, and untested task illumination or color fidelity in the Orion cabin. Discussion: While OLFs aptly attenuate 480-nm light from our tunable LED lamp in the Lighting Lab’s controlled environment, they remain untested within the Orion cabin on OCLS lamps. Future tests include Orion cabin illumination optimization for appropriate Lux delivery and ensuring task/color fidelity with OLFs deployed. Adequate OCLS cooling should be similarly assessed. Other safety testing includes OLF frangibility/flammability/off-gassing in an enriched-O 2 /hypobaric environment. Together, these data will demonstrate OLFs provide a viable workaround for maintaining CCE further ensuring mission safety and success.

Carlos Rene Dostal↗
DOE OSTI2022

Modulation of recombination zone position for white perovskite/organic emitter hybrid light-emitting devices

We report metal halide perovskites present specific challenges as emitters in large area, surface emission lighting devices. Among these challenges is the vast difference in carrier mobilities between the perovskite and many organic buffer layers typically used in such device fabrication as transport and blocking layers. This can make it difficult to engineer recombination to achieve white emitting devices generally. However, in this work, we introduce unique modulation of excitonic confinement within the perovskite layer of the device stack to control overall placement of the recombination zone. This results in a white light emitter that is bright and highly tunable, providing a path to realize white perovskite related light-emitting devices.

42 ENGINEERING↗
NASA NTRS2004

Slit Function Measurement of An Imaging Spectrograph Using Fourier Transform Techniques

Knowledge of a spectrograph slit function is necessary to interpret the unresolved lines in an observed spectrum. A theoretical slit function can be calculated from the sizes of the entrance slit, the detector aperture when it functions as an exit slit, the dispersion characteristic of the disperser, and the point spread function of the spectrograph. A measured slit function is preferred to the theoretical one for the correct interpretation of the spectral data. In a scanning spectrometer with a single exit slit, the slit function is easily measured. In a fixed grating/or disperser spectrograph, illuminating the entrance slit with a near monochromatic light from a pre-monochrmator or a tunable laser and varying the wavelength of the incident light can measure the slit function. Even though the latter technique had been used successfully for the slit function measurements, it had been very laborious and it would be prohibitive to an imaging spectrograph or a multi-object spectrograph that has a large field of view. We explore an alternative technique that is manageable for the measurements. In the proposed technique, the imaging spectrograph is used as a detector of a Fourier transform spectrometer. This method can be applied not only to an IR spectrograph but also has a potential to a visible/UV spectrograph including a wedge filter spectrograph. This technique will require a blackbody source of known temperature and a bolometer to characterize the interferometer part of the Fourier Transform spectrometer. This pa?er will describe the alternative slit function measurement technique using a Fourier transform spectrometer.

Park, Hongwoo↗
NASA NTRS1998

Tunable Microwave Components for Ku- and K-Band Satellite Communications

The use of conductor/ferroelectric/dielectric thin film multilayer structures for frequency and phase agile components at frequencies at and above the Ku-band will be discussed. Among these components are edge coupled filters, microstripline ring resonators, and phase shifters. These structures were implemented using SrTiO3 (STO) ferroelectric thin films, with gold or YBa2Cu3O7-d (YBCO) high temperature superconducting (HTS) microstrip fines deposited by laser ablation on LaAlO3 (LAO) substrates. The performance of these structures in terms of tunability, operating temperature, frequency, and dc bias will be presented. Because of their small size, light weight, and low loss, these tunable microwave components are being studied very intensely at NASA as well as the commercial communication industry. An assessment of the progress made so far, and the issues yet to be solved for the successful integration of these components into the aforementioned communication systems will be presented.

Miranada, F. A.↗
DOE OSTI2022

Controlling Selectivity in Plasmonic Catalysis: Switching Reaction Pathway from Hydrogenation to Homocoupling Under Visible‐Light Irradiation

Abstract Plasmonic catalysis enables the use of light to accelerate molecular transformations. Its application to the control reaction selectivity is highly attractive but remains challenging. Here, we have found that the plasmonic properties in AgPd nanoparticles allowed different reaction pathways for tunable product formation under visible‐light irradiation. By employing the hydrogenation of phenylacetylene as a model transformation, we demonstrate that visible‐light irradiation can be employed to steer the reaction pathway from hydrogenation to homocoupling. Our data showed that the decrease in the concentration of H species at the surface due to plasmon‐enhanced H 2 desorption led to the control in selectivity. These results provide important insights into the understanding of reaction selectivity with light, paving the way for the application of plasmonic catalysis to the synthesis of 1,3‐diynes, and bringing the vision of light‐driven transformations with target selectivity one step closer to reality.

Peiris, Erandi↗
NASA NTRS1995

The development of a tunable, single-frequency ultraviolet laser source for UV filtered Rayleigh scattering

We present the development of a flexible, high power, narrow line width, tunable ultraviolet source for diagnostic application. By frequency tripling the output of a pulsed titanium-sapphire laser, we achieve broadly tunable (227-360 nm) ultraviolet light with high quality spatial and spectral resolution. We also present the characterization of a mercury vapor cell which provides a narrow band, sharp edge absorption filter at 253.7 nm. These two components form the basis for the extension of the Filtered Rayleigh Scattering technique into the ultraviolet. The UV-FRS system is comprised of four pieces: a single frequency, cw tunable Ti:Sapphire seeding source; a high-powered pulsed Ti:Sapphire oscillator; a third harmonic generator system; and an atomic mercury vapor filter. In this paper we discuss the development and characterization of each of these elements.

Finkelstein, N.↗
NASA NTRS1974

Investigation of laser dynamics, modulation and control by means of intra-cavity time varying perturbation

Projects aimed at the generation of tunable visible, infrared, and ultraviolet light, and on the control of this light by means of novel mode-locking and modulation techniques are discussed. During this period the following projects have been active: (1) studies of transient mode-locking of the Nd:YAG laser and the application of short optical pulses; (2) experimental investigations of the Na-Xe excimer laser system; (3) further development of techniques for vacuum ultraviolet holography; and (4) theoretical and initial experimental studies of a new device which should prove very useful for both infrared up-conversion and generation of tunable UV radiation - a two-photon resonantly pumped frequency converter.

Harris, S. E.↗
DOE OSTI2025

Multi-Beam-Energy Control Unit Based on Triple-Bend Achromats

X-ray free electron lasers (XFELs) are the new generation of particle accelerator-based light sources, capable of producing tunable, high-power X-ray pulses that are increasingly vital across various scientific disciplines. Recently, continuous-wave (CW) XFELs driven by superconducting linear accelerators have garnered significant attention due to their ability to enhance availability by supporting multiple undulator lines simultaneously. In this paper, we introduce a novel delay system comprising four triple-bend achromats (TBAs). This delay system was combined with fast kickers and can be employed to generate electron beams on a bunch-to-bunch basis in a CW-XFEL facility. Based on the parameters of the Shanghai High-Repetition-Rate XFEL and Extreme Light Facility, start-to-end simulations demonstrate that the TBA-based delay system achieves excellent electron beam qualities while providing a wide beam-energy-tuning range from 1.39 to 8 GeV.

43 PARTICLE ACCELERATORS↗
DOE OSTI2021

Ultrafast all-optical diffraction switching using semiconductor metasurfaces

Ultrafast all-optical switching using Mie resonant metasurfaces requires both on-demand tunability of the wavefront of the light and ultrafast time response. However, devising a switching mechanism that has a high contrast between its “on” and “off” states without compromising speed is challenging. Here, we report the design of a tunable Mie resonant metasurface that achieves this behavior. Our approach utilizes a diffractive array of semiconductor resonators that support both dipolar and quadrupolar Mie resonances. By balancing the strengths of the dipole and quadrupole resonances, we can suppress radiation into the first diffraction order, thus creating a clearly delineated “off”-state at the operating wavelength. Then, we use optical injection of free- carriers to spectrally shift the multipoles and rebalance the multipole strengths, thereby enabling radiation into the diffraction order—all on an ultrafast timescale. We demonstrate ultrafast off-to-on switching with I on /I off ≈ 5 modulation of the diffracted intensity and ultrafast on-to-off switching with Ion/Ioff ≈ 9 modulation. Furthermore, both switches exhibit a fast τ tr ≈ 2.7 ps relaxation time at 215 μJ cm -2 pump fluence. Further, we show that for higher fluences, the temporal response of the metasurface is governed by thermo-optic effects. This combination of multipole engineering with lattice diffraction opens design pathways for tunable metasurface-based integrated devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Debonding-on-demand reversible adhesives via heat or light with competitive adhesion strength to conventional epoxy adhesives

Stimuli responsive debonding-on-demand (DoD) reversible adhesives are of great interest for the circular economy. However, the reversible adhesives developed so far often lack competitive adhesion strength in a bonding state. In this work, reversible epoxy adhesives based on Diels–Alder (DA) chemistry were developed and exhibited a competitive adhesion strength (e.g., 12 – 16 MPa of a lap shear strength) to commercial non-reversible epoxy adhesives. The reversible epoxy formulation showed superior thermal stability up to 110°C, and transition to a debonding state in the order of 0.1 MPa at 140°C, consequently, an on/off-type debonding behavior. The transition to a debonding state was attributed to crosslinking density control (e.g., decrease by 33% – 49%) through the reversible DA chemistry and the proximity to the glass transition. Next, for debonding by light stimulus, photothermal refractory plasmonic titanium nitride (TiN) nanoparticles were incorporated in the reversible epoxy, which can generate the required heat for debonding upon exposure to visible light. Photothermal debonding allows for precise debonding at target areas and tunable adhesion strength by controlling the exposure area and light intensity. The DA adhesive formulations containing 0.5 wt.% TiN nanoparticles presented a debonding state with zero adhesion under light exposure with intensity of 1670 mW/cm 2 (inducing 140°C). Even after three cycles of reattachment, the DA adhesive formulations retained 96% of the pristine sample’s adhesion strength measured at 110°C. Therefore, the DA adhesives are attractive candidates as reversible DoD systems applicable in higher temperatures.

42 ENGINEERING↗
DOE OSTI2022

Fast Near-Infrared Photodetection Using III–V Colloidal Quantum Dots

Colloidal quantum dots (CQDs) are promising materials for infrared (IR) light detection due to their tunable bandgap and their solution processing; however, to date, the time response of CQD IR photodiodes is inferior to that provided by Si and InGaAs. It is reasoned that the high permittivity of II–VI CQDs leads to slow charge extraction due to screening and capacitance, whereas III–Vs—if their surface chemistry can be mastered—offer a low permittivity and thus increase potential for high-speed operation. In initial studies, it is found that the covalent character in indium arsenide (InAs) leads to imbalanced charge transport, the result of unpassivated surfaces, and uncontrolled heavy doping. Surface management using amphoteric ligand coordination is reported, and it is found that the approach addresses simultaneously the In and As surface dangling bonds. The new InAs CQD solids combine high mobility (0.04 cm 2 V -1 s -1 ) with a 4× reduction in permittivity compared to PbS CQDs. Finally, the resulting photodiodes achieve a response time faster than 2 ns—the fastest photodiode among previously reported CQD photodiodes—combined with an external quantum efficiency (EQE) of 30% at 940 nm.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Confinement of excited states in two-dimensional, in-plane, quantum heterostructures

Two-dimensional (2D) semiconductors are promising candidates for optoelectronic application and quantum information processes due to their inherent out-of-plane 2D confinement. In addition, they offer the possibility of achieving low-dimensional in-plane exciton confinement, similar to zero-dimensional quantum dots, with intriguing optical and electronic properties via strain or composition engineering. However, realizing such laterally confined 2D monolayers and systematically controlling size-dependent optical properties remain significant challenges. Here, we report the observation of lateral confinement of excitons in epitaxially grown in-plane MoSe 2 quantum dots (~15-60 nm wide) inside a continuous matrix of WSe 2 monolayer film via a sequential epitaxial growth process. Various optical spectroscopy techniques reveal the size-dependent exciton confinement in the MoSe 2 monolayer quantum dots with exciton blue shift (12-40 meV) at a low temperature as compared to continuous monolayer MoSe 2 . Finally, single-photon emission (g 2 (0) ~ 0.4) was also observed from the smallest dots at 1.6 K. Our study opens the door to compositionally engineered, tunable, in-plane quantum light sources in 2D semiconductors.

42 ENGINEERING↗
DOE OSTI2026

Single-particle detection of enhanced polarizability in Au-decorated semiconducting nanorods via scanning dielectric microscopy

Hybrid nanostructures that combine semiconducting and metallic components offer great potential for photothermal therapy, optoelectronics, and sensing, by integrating tunable optical properties with enhanced light absorption and charge transport. Boosting the integrated performance of these hybrid systems demands techniques capable of probing local variations of the physical properties inaccessible to bulk analysis. Here, we report the single-particle dielectric characterization of hybrid, semiconducting bismuth sulfide (Bi 2 S 3 ) nanorods (NR) decorated with metallic Au nanoparticles (NP), employing scanning dielectric microscopy, which uses electrostatic force microscopy in combination with finite-element numerical simulations. We reveal a pronounced enhancement in the local dielectric response of Bi2S3 upon Au decoration, attributed to interfacial polarization and electron transfer from Au to the Bi 2 S 3 matrix, thus suggesting a enhanced metallic-like polarizability at the single-particle level. Numerical simulations show that the response is dominated by the vertical component of the permittivity and that the decorating metallic Au NP produce only moderate shielding of the semiconductor Bi 2 S 3 NR core, indicating that the large increase in the dielectric response originates primarily from intrinsic modifications within the NR. Overall, these findings provide direct insight into structure–property relationships at the single-particle level, supporting the rational design of advanced hybrid nanostructures with tailored electronic functionalities.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Unraveling H2 chemisorption and physisorption on metal decorated graphene using quantum Monte Carlo

Molecular hydrogen has the potential to significantly reduce the use of carbon dioxide emitting energy processes. However, hydrogen gas storage is a major bottleneck for its large-scale use as current storage methods are energy intensive. Among different storage methods, physisorbing molecular hydrogen at ambient pressure and temperatures is a promising alternative—particularly in light of the advancements in tunable lightweight nanomaterials and high throughput screening methods. Nonetheless, understanding hydrogen adsorption in well-defined nanomaterials remains experimentally challenging and reference information is scarce despite the proliferation of works predicting hydrogen adsorption. We focus on Li, Na, Ca, and K, decorated graphene sheets as substrates for molecular hydrogen adsorption, and compute the most accurate adsorption energies available to date using quantum diffusion Monte Carlo (DMC). Building on our previous insights at the density functional theory (DFT) level, we find that a weak covalent chemisorption of molecular hydrogen, known as Kubas interaction, is feasible on Ca decorated graphene according to DMC, in agreement with DFT. This finding is in contrast to previous DMC predictions of the 4H2/Ca+ gas cluster (without graphene) where chemisorption is not favored. However, we find that the adsorption energy of hydrogen on metal decorated graphene according to a widely used DFT method is not fully consistent with DMC. The reference adsorption energies reported herein can be used to find better work-horse methods for application in large-scale modeling of hydrogen adsorption. Furthermore, the implications of this work affect strategies for finding suitable hydrogen storage materials and high-throughput methods.

Chemistry↗
DOE OSTI2020

Topological nanophotonics for photoluminescence control

Rare-earth-doped nanocrystals are emerging light sources that can produce tunable emissions in colours and lifetimes, which has been typically achieved in chemistry and material science. However, one important optical challenge – polarization of photoluminescence – remains largely out of control by chemistry methods. Control over photoluminescence polarization can be gained via coupling of emitters to resonant nanostructures such as optical antennas and metasurfaces. However, the resulting polarization is typically sensitive to position disorder of emitters, which is difficult to mitigate. Recently, new classes of disorder-immune optical systems have been explored within the framework of topological photonics. Here we explore disorder-robust topological arrays of Mie-resonant nanoparticles for polarization control of photoluminescence of nanocrystals. We demonstrate polarized emission from rare-earth-doped nanocrystals governed by photonic topological edge states supported by zigzag arrays of dielectric resonators. We verify the topological origin of polarized photoluminescence by comparing emission from nanoparticles coupled to topologically trivial and nontrivial arrays of nanoresonators. We expect that our results may open a new direction in the study of topology-enable emission properties of topological edge states in many photonic systems.

36 MATERIALS SCIENCE↗
NASA NTRS1973

Investigation of laser dynamics, modulation and control by means of intra-cavity time varying perturbation

Work continued on a number of projects aimed at the generation of tunable visible, infrared, and ultraviolet light; and on the control of this light by means of novel mode-locking and modulation techniques. Progress is summarized for the following projects: (1) the transient modelocking of the Nd:YAG laser and application of short optical pulses; (2) studies of the sodium-xenon excimer laser; (3) development of techniques for vacuum ultraviolet holography; and (4) studies of multiple photon pumped xenon and argon excimer lasers.

Harris, S. E.↗