Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “tunable light”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Tunable infrared pixels having unpatterned graphene layer and conductive metasurface

A monolithically integrated, tunable infrared pixel comprises a combined broadband detector and graphene-enabled tunable metasurface filter that operate as a single solid-state device with no moving parts. Functionally, tunability results from the plasmonic properties of graphene that are acutely dependent upon the carrier concentration within the infrared. Voltage induced changes in graphene's carrier concentration can be leveraged to change the metasurface filter's transmission thereby altering the “colors” of light reaching the broadband detector and hence its spectral responsivity. The invention enables spectrally agile infrared detection with independent pixel-to-pixel spectral tunability.

Beechem, III, Thomas Edwin↗
DOE OSTI2016

A cylindrical quadrupole ion trap in combination with an electrospray ion source for gas-phase luminescence and absorption spectroscopy

A relatively simple setup for collection and detection of light emitted from isolated photo-excited molecular ions has been constructed. It benefits from a high collection efficiency of photons, which is accomplished by using a cylindrical ion trap where one end-cap electrode is a mesh grid combined with an aspheric condenser lens. The geometry permits nearly 10% of the emitted light to be collected and, after transmission losses, approximately 5% to be delivered to the entrance of a grating spectrometer equipped with a detector array. The high collection efficiency enables the use of pulsed tunable lasers with low repetition rates (e.g., 20 Hz) instead of continuous wave (cw) lasers or very high repetition rate (e.g., MHz) lasers that are typically used as light sources for gas-phase fluorescence experiments on molecular ions. A hole has been drilled in the cylinder electrode so that a light pulse can interact with the ion cloud in the center of the trap. Simulations indicate that these modifications to the trap do not significantly affect the storage capability and the overall shape of the ion cloud. The overlap between the ion cloud and the laser light is basically 100%, and experimentally >50% of negatively charged chromophore ions are routinely photodepleted. The performance of the setup is illustrated based on fluorescence spectra of several laser dyes, and the quality of these spectra is comparable to those reported by other groups. Finally, by replacing the optical system with a channeltron detector, we demonstrate that the setup can also be used for gas-phase action spectroscopy where either depletion or fragmentation is monitored to provide an indirect measurement on the absorption spectrum of the ion.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Electrically tunable terahertz wave modulator based on complementary metamaterial and graphene

In this paper, we design and numerically demonstrate an electrically controllable light-matter interaction in a hybrid material/metamaterial system consisting of an artificially constructed cross cut-wire complementary metamaterial and an atomically thin graphene layer to realize terahertz (THz) wave modulator. By applying a bias voltage between the metamaterial and the graphene layer, this modulator can dynamically control the amplitude and phase of the transmitted wave near 1.43 THz. Moreover, the distributions of current density show that this large modulation depth can be attributed to the resonant electric field parallel to the graphene sheet. Therefore, the modulator performance indicates the enormous potential of graphene for developing sophisticated THz communication systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Broadband Liquid Crystal Tunable Metasurfaces in the Visible: Liquid Crystal Inhomogeneities Across the Metasurface Parameter Space

Optical metasurfaces—planar nanostructured devices that can arbitrarily tailor the wavefront of light—may be reconfigured by changing their dielectric environment. The application of external stimuli to liquid crystals is a particularly promising means of tuning the optical properties of embedded metasurfaces because of liquid crystals' large and broadband optical anisotropy. However, the detailed behavior of liquid crystals immediately adjacent to the nanostructured meta-atoms elements is often overlooked, despite the optics of the device depending sensitively on this behavior (e.g., the spectral position of the meta-atom resonances). This is of increasing concern as the wavelength of operation further approaches the short-wavelength end of the visible spectrum and, therefore, the length scale of the inhomogeneities in the liquid crystal director field. In this manuscript, we undertake a fully comprehensive study, across the metasurface geometrical parameter space, of broadband (450-700 nm) all-dielectric liquid crystal tunable metasurfaces operating in the visible. Here, through combined experimental characterization, liquid crystal modeling, and optical simulations, we reveal and quantify the improved accuracy with which the optical properties of the liquid crystal tunable metasurfaces may be described, and identify the underlying physical mechanism: the three-dimensional spatial overlap of the liquid crystal director field and metasurface optical near fields in the vicinity of the meta-atoms.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Wideband tunable up-converting optoelectronic oscillator based on gain–loss compensation technology and stimulated Brillouin scattering

An optically wideband tunable up-converting optoelectronic oscillator (OEO) based on stimulated Brillouin scattering and gain–loss compensation is demonstrated and theoretically analyzed. In the proposed structure, Brillouin narrowband filter technique is implemented by introducing two pump lights with the frequency interval twice the Brillouin frequency shift (v{sub b}). The overlapping of the gain and the loss spectrum is used to realize a wideband tunable OEO. As a consequence, the tunability of the wideband of the output microwave signal at f{sub m}+2v{sub b} from 22.4 to 61.4 GHz can be realized by changing the signal under testing from 1 to 40 GHz. In addition, the transfer function of the system is given and the single sideband (SSB) phase noise is also evaluated theoretically. And the theoretical simulated the SSB phase noise is − 116.1 dBc/Hz at the 10 kHz offset when the f{sub m} = 25 GHz. Not only the OEO can convert a low-frequency IF signal to a high-frequency signal without introducing any high-Q electrical filter, but the frequency of the output signal is high enough and widely tunable. Because of the high frequency tunable capacity, the up-converting OEO might have a potential application in radar communication and millimeter wave generation systems.

42 ENGINEERING↗
DOE OSTI2022

Simple thermal vapor deposition process for and characterization of n-type indium oxysulfide thin films

The search continues for alternative nontoxic n-type electron transport layers in optoelectronic thin-film devices. Indium oxysulfide, In 2 (O,S) 3 , represents one promising material for this application, especially when paired with chalcogenide absorber layers. The ternary nature of the composition allows for electrical conductivity and optical bandgap tuning by tailoring the sulfur to oxygen ratio in the oxysulfide alloy. However, thin films of In 2 (O,S) 3 are typically deposited only by chemical bath deposition or plasma-enhanced atomic layer deposition. Here we report deposition of thin films of In 2 (O,S) 3 in a custom-built thermal reactor using only water vapor and hydrogen sulfide as the coreactants. This advance is enabled by the use of a recently reported, highly reactive indium formamidinate precursor. As shown by x-ray photoelectron spectroscopy, the composition can be tuned from pure In 2 (O,S) 3 to pure In 2 S 3 by varying the ratio of cycles employing water or hydrogen sulfide. The oxygen to the sulfur ratio in the film can be controlled by altering the dose sequence, although films typically contain more sulfur than would be expected naively from the percentage of hydrogen sulfide doses in the deposition recipe. Rutherford backscattering spectrometry confirms the composition is sulfur-rich relative to the dosing ratio. Structural characterization indicates films are relatively amorphous in nature. Electrically, these films offer reasonably constant electron mobility at different O:S ratios, with an electron concentration tunable over 4 orders of magnitude. These oxysulfide films possess a higher indirect bandgap than their oxygen-free indium sulfide counterparts, indicating higher transmittance to blue light. These indium oxysulfide films may be suitable candidates for electron transport layers in thin-film solar cells where their wider bandgap might result in higher optical transparency and thus short circuit current density, while the tunability of their conduction band offset with an absorber layer may result in higher open circuit voltage.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Electric and magnetic behaviors observed in NiO-based thin films under light-irradiation

We report the room-temperature ferromagnetic properties that can be tuned by light irradiation in the Li and Mn co-doped NiO films (LMNO) grown by the spinning coating. The optical tunable magnetic behavior is enhanced by the increase of the Li doping concentration. First-principle calculations reveal that the Li doping plays key roles in the optical tuned magnetic behavior, which brings a 3d-like impurity state to enhance a significant hybridization between the Mn{sup 3+} 3d state and the impurity band, thus strengthening the ferromagnetic coupling effects. Additionally, it can tune the band gap of the LMNO films and produce more holes under the light irradiation, enhancing the optical tuned magnetic behavior.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

High-Temperature Photoluminescence of CsPbX 3 (X = Cl, Br, I) Nanocrystals

Recent synthetic developments have generated intense interest in the use of cesium lead halide perovskite nanocrystals for light-emitting applications. This work presents the photoluminescence (PL) of cesium lead halide perovskite nanocrystals with tunable halide composition recorded as function of temperature from 80 to 550 K. CsPbBr 3 nanocrystals show the highest resilience to temperature while chloride-containing samples show relatively poorer preservation of photoluminescence at elevated temperatures. Thermal cycling experiments show that PL loss of CsPbBr 3 is largely reversible at temperatures below 450 K, but shows irreversible degradation at higher temperatures. Time-resolved measurements of CsPbX 3 samples show an increase in the PL lifetime with temperature elevation, consistent with exciton fission to form free carriers, followed by a decrease in the apparent PL lifetime due to trapping. In conclusion, PL persistence measurements and time-resolved spectroscopies implicate thermally assisted trapping, most likely to halogen vacancy traps, as the mechanism of reversible PL loss.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Enhanced photocatalytic degradation of phenol over Ag3PO4-BiOCl1−xBrx composites

Highlights: • Ag{sub 3}PO{sub 4}-BiOCl{sub 1−x}Br{sub x} composites were successfully synthesized and characterized. • The band energy of composites can be tunable by solid-solution strategy. • Appropriate band-gap structure facilitates charge separation property and light absorption. - Abstract: In this paper, a series of Ag{sub 3}PO{sub 4}-BiOCl{sub 1−x}Br{sub x} composites with adjustable band gap has been fabricated by using a facile two-step synthetic method. The photocatalytic activity of Ag{sub 3}PO{sub 4}-BiOCl{sub 1−x}Br{sub x} was evaluated by photocatalytic decomposition of phenol aqueous solution under simulated solar light irradiation. The result shows that Ag{sub 3}PO{sub 4}-BiOCl{sub 0.75}Br{sub 0.25} (1:5) composite possesses the best photocatalytic activity among all the as-prepared samples. The photocatalytic activity of Ag{sub 3}PO{sub 4}-BiOCl can be enhanced mainly owing to the strong light absorption ability by loading Ag{sub 3}PO{sub 4} on the surface of BiOCl, while the photocatalytic activities of Ag{sub 3}PO{sub 4}-BiOCl{sub 1−x}Br{sub x} (x = 0.25, 0.5, 0.75 and 1) composites could be enhanced by restraining the recombination of photo-generated electron-hole pairs. The enhanced solar-light photocatalytic activities of Ag{sub 3}PO{sub 4}-BiOCl{sub 1−x}Br{sub x} composites could be ascribed to the adjustable energy band structure, which facilitates the separation of photoinduced carriers. In addition, superoxide radicals (O{sub 2}{sup −}), holes (h{sup +}) and OH are considered to dominate the photocatalytic degration process. Moreover, a possible mechanism of deep understanding on the base of experimental results was proposed.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Self-powered and broadband photodetectors based on graphene/ZnO/silicon triple junctions

A self-powered photodetector with ultrahigh sensitivity, fast photoresponse, and wide spectral detectivity covering from 1000 nm to 400 nm based on graphene/ZnO/Si triple junctions has been designed, fabricated, and demonstrated. In this device, graphene serves as a transparent electrode as well as an efficient collection layer for photogenerated carriers due to its excellent tunability of Fermi energy. The ZnO layer acts as an antireflection layer to trap the incident light and enhance the light absorption. Furthermore, the insertion of the ZnO layer in between graphene and Si layers can create build-in electric field at both graphene/ZnO and ZnO/Si interfaces, which can greatly enhance the charge separation of photogenerated electron and hole pairs. As a result, the sensitivity and response time can be significantly improved. It is believed that our methodology for achieving a high-performance self-powered photodetector based on an appropriate design of band alignment and optical parameters can be implemented to many other material systems, which can be used to generate unique optoelectronic devices for practical applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Sensitive singular-phase optical detection without phase measurements with Tamm plasmons

Spectrally-tailored interactions of light with material interfaces have offered many exciting applications in sensing, photo-detection, and optical energy conversion. In particular, complete suppression of light reflectance at select frequencies accompanied by sharp phase variations in the reflected signal forms the basis for the development of ultra-sensitive singular-phase optical detection schemes such as Brewster and surface plasmon interferometry. However, both the Brewster effect and surface-plasmon-mediated absorption on planar interfaces are limited to one polarization of the incident light and oblique excitation angles, and may have limited bandwidth dictated by the material dielectric index and plasma frequency. To alleviate these limitations, we design narrow-band super-absorbers composed of plasmonic materials embedded into dielectric photonic nanostructures with topologically-protected interfacial Tamm plasmon states. These structures have planar geometry and do not require nanopatterning to achieve perfect absorption of both polarizations of the incident light in a wide range of incident angles, including the normal incidence. Their absorption lines are tunable across a very broad spectral range via engineering of the photon bandstructure of the dielectric photonic nanostructures to achieve reversal of the geometrical phase across the interface with the plasmonic absorber. We outline the design strategy to achieve perfect absorptance in Tamm structures with dissipative losses via conjugate impedance matching. We further demonstrate via modeling how these structures can be engineered to support sharp asymmetric amplitude resonances, which can be used to improve the sensitivity of optical sensors in the amplitude-only detection scheme that does not require use of bulky and expensive ellipsometry equipment

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Absolute timing calibration of the Resolve microcalorimeter spectrometer on the X-ray Imaging and Spectroscopy Mission

The Resolve microcalorimeter spectrometer on the X-ray Imaging and Spectroscopy Mission (XRISM) is designed to have a good timing capability with the mission-level requirement of 1 ms as the absolute time tagging accuracy to suffice the needs for observatory science. In the ground calibration campaign, the absolute and relative timing offsets were measured using pulsed X-rays from the modulated X-ray sources. These offsets were used to determine calibration parameters, the Resolve timing coefficients, which are used in the offline correction of event times. In the orbit, reevaluation of the timing coefficients was carried out using the Crab pulsar, which was observed in two periods, one in the performance verification phase and the other in the guest observation phase. We report the absolute timing calibration of XRISM/Resolve using the ground and in-orbit data. Although the requirement is likely satisfied with the ground parameters, the timing coefficients have been refined using the in-orbit calibration to improve the timing accuracy. In addition, for the first time, we present the interpretation of the absolute timing offset originating from the analog and digital processing of X-ray events unique to a microcalorimeter spectrometer and present a complete view of the timing error of the Resolve instrument.

Astronomy and AstroPhysics↗
DOE OSTI2021

Semiconductor quantum dots: Technological progress and future challenges

In quantum-confined semiconductor nanostructures, electrons exhibit distinctive behavior compared with that in bulk solids. This enables the design of materials with tunable chemical, physical, electrical, and optical properties. Zero-dimensional semiconductor quantum dots (QDs) offer strong light absorption and bright narrowband emission across the visible and infrared wavelengths and have been engineered to exhibit optical gain and lasing. These properties are of interest for imaging, solar energy harvesting, displays, and communications. Here, we offer an overview of advances in the synthesis and understanding of QD nanomaterials, with a focus on colloidal QDs, and discuss their prospects in technologies such as displays and lighting, lasers, sensing, electronics, solar energy conversion, photocatalysis, and quantum information.

García de Arquer, F. Pelayo↗
NASA NTRS2016

Polarization Dependent Whispering Gallery Modes in Microspheres

A tunable resonant system is provided and includes a microsphere that receives an incident portion of a light beam generated via a light source, the light beam having a fundamental mode, a waveguide medium that transmits the light beam from the light source to the microsphere, and a polarizer disposed in a path of the waveguide between the light source and the microsphere. The incident portion of the light beam creates a fundamental resonance inside the microsphere. A change in a normalized frequency of the wavelength creates a secondary mode in the waveguide and the secondary mode creates a secondary resonance inside the microsphere.

Adamovsky, Grigory↗
NASA NTRSDate not supplied

Absorption Laser Differential Interferometry for Simultaneous Colinear Flow Property and Fluctuation Measurements

An absorption laser differential interferometer (A-LDI) was constructed and tested in an effort to simultaneously and colinearly measure flow properties (pressure, temperature, concentration) and flow fluctuations (changes in optical path length). Whereas typical LDI and focused LDI (FLDI) systems use fixed wavelength lasers as the light source (often either green at approximately 532 nm or red at approximately 630 nm), a tunable 760 nm diode laser was used to probe the A-band absorption spectrum of molecular oxygen. The A-LDI system was used to measure O2 absorption and flow fluctuations in a sub-atmospheric pressure-controlled test cell, with absorption profiles from direct absorption and wavelength modulation absorption matching simulated results, while simultaneously being sensitive to high frequency fluctuations from jets of either compressed air or 100% O2 from a gas bottle. The A-LDI system was also installed at the NASA Langley Research Center Probe Calibration Tunnel to assess the freestream flow state in a Mach 3.5 flow. LDI measurements of the freestream indicated increasing amplitudes of flow fluctuations with increasing stagnation pressure at a fixed stagnation temperature, while absorption results demonstrated sensitivity to freestream pressure changes.

Joshua M. Weisberger↗
DOE OSTI2021

Light quantum control of persisting Higgs modes in iron-based superconductors

The Higgs mechanism, i.e., spontaneous symmetry breaking of the quantum vacuum, is a cross-disciplinary principle, universal for understanding dark energy, antimatter and quantum materials, from superconductivity to magnetism. Unlike one-band superconductors (SCs), a conceptually distinct Higgs amplitude mode can arise in multi-band, unconventional superconductors via strong interband Coulomb interaction, but is yet to be accessed. Here we discover such hybrid Higgs mode and demonstrate its quantum control by light in iron-based high-temperature SCs. Using terahertz (THz) two-pulse coherent spectroscopy, we observe a tunable amplitude mode coherent oscillation of the complex order parameter from coupled lower and upper bands. The nonlinear dependence of the hybrid Higgs mode on the THz driving fields is distinct from any known SC results: we observe a large reversible modulation of resonance strength, yet with a persisting mode frequency. Together with quantum kinetic modeling of a hybrid Higgs mechanism, distinct from charge-density fluctuations and without invoking phonons or disorder, our result provides compelling evidence for a light-controlled coupling between the electron and hole amplitude modes assisted by strong interband quantum entanglement. Such light-control of Higgs hybridization can be extended to probe many-body entanglement and hidden symmetries in other complex systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Tunable orbital angular momentum in high-harmonic generation

Optical vortices are currently one of the most intensively studied topics in optics. These light beams, which carry orbital angular momentum (OAM), have been successfully utilized in the visible and infrared in a wide variety of applications. Moving to shorter wavelengths may open up completely new research directions in the areas of optical physics and material characterization. Here, we report on the generation of extreme-ultraviolet optical vortices with femtosecond duration carrying a controllable amount of OAM. From a basic physics viewpoint, our results help to resolve key questions such as the conservation of angular momentum in highly nonlinear light–matter interactions, and the disentanglement and independent control of the intrinsic and extrinsic components of the photon’s angular momentum at short-wavelengths. Finally, the methods developed here will allow testing some of the recently proposed concepts such as OAM-induced dichroism, magnetic switching in organic molecules and violation of dipolar selection rules in atoms.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Stable Perovskite Core-Shell Nanocrystals as Down-Converting Phosphors for Solid State Lighting

Colloidal perovskite quantum dots (QDs) or nanocrystals (NCs) with structure of CsPbX 3 (X = Cl, Br, I) are promising materials as down-converting phosphors due to their high quantum yield up to >90%, extremely narrow emission band ~15-30 nm, and tunable emission wavelengths of ~410-700 nm via size or composition control. Compared to other QD materials, the optical and electronic properties of perovskite NCs are much more tolerant to defects so highly efficient light-emitting NCs can be easily prepared without carefully removing surface defects. Also, precision size control is not required for obtaining perovskite NCs with narrow emission <30 nm and can greatly enhance the reproducibility and yield rate during mass production. The challenges in using perovskite NCs as LED phosphors are their hygroscopic nature and self-absorption as observed from other QDs. We propose to synthesize core-shell structure perovskite NCs to improve their stability by over-coating a SiO 2 layer, followed by further sol-gel processing into stable micro-sized glass beads. To increase Stokes shift and avoid self-absorption, core/graded-shell/shell structure such as CsSnBr 3 /CsSn 1-x Pb x Br 3 /CsPbBr 3 NCs will be prepared, similar to a concept we demonstrated before in CdSe/Cd 1-x ZnxSe 1-y S y /ZnS structure with significantly separated absorption and emission bands. These NC materials will be integrated into films and used as remote or on-chip downconverters for high efficiency, high CRI and warm white LED. To achieve this goal, PhosphorTech Corporation (PTC) has teamed with Georgia Tech (GT) to develop this unique perovskite system for pcLEDs that offers the promise of high luminous efficacy over a broad temperature and optical flux range.

36 MATERIALS SCIENCE↗