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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Damping and structural control of the JPL phase 0 testbed structure

This paper describes recent advances in structural quieting technology as applied to active truss structures intended for high precision space based optics applications. The active structure incorporates piezoelectric active members which exert control forces internal to the structure and thereby improve the structure's dimensional stability. The control architecture involves two layers of feedback control. The first utilizes collocated measurements of force and velocity at the active member to achieve active damping, the second utilizes noncollocated measurements of acceleration at the location of a simulated optical component to achieve structural stabilization. The local control loops are based on the concept of impedance matching, the global control loops are designed using robust control methods. These two levels of control are intended to operate simultaneously; however, in this paper each approach is applied individually. The combined implementation is left for future work.

Fanson, James L.↗
NASA NTRS2011

NASA Tech Briefs, May 2011

Topics covered include: 1) Method to Estimate the Dissolved Air Content in Hydraulic Fluid; 2) Method for Measuring Collimator-Pointing Sensitivity to Temperature Changes; 3) High-Temperature Thermometer Using Cr-Doped GdAlO3 Broadband Luminescence; 4)Metrology Arrangement for Measuring the Positions of Mirrors of a Submillimeter Telescope; 5) On-Wafer S-Parameter Measurements in the 325-508-GHz Band; 6) Reconfigurable Microwave Phase Delay Element for Frequency Reference and Phase-Shifter Applications; 7) High-Speed Isolation Board for Flight Hardware Testing; 8) High-Throughput, Adaptive FFT Architecture for FPGA-Based Spaceborne Data Processors; 9) 3D Orbit Visualization for Earth-Observing Missions; 10) MaROS: Web Visualization of Mars Orbiting and Landed Assets; 11) RAPID: Collaborative Commanding and Monitoring of Lunar Assets; 12) Image Segmentation, Registration, Compression, and Matching; 13) Image Calibration; 14) Rapid ISS Power Availability Simulator; 15) A Method of Strengthening Composite/Metal Joints; 16) Pre-Finishing of SiC for Optical Applications; 17) Optimization of Indium Bump Morphology for Improved Flip Chip Devices; 18) Measuring Moisture Levels in Graphite Epoxy Composite Sandwich Structures; 19) Marshall Convergent Spray Formulation Improvement for High Temperatures; 20) Real-Time Deposition Monitor for Ultrathin Conductive Films; 21) Optimized Li-Ion Electrolytes Containing Triphenyl Phosphate as a Flame-Retardant Additive; 22) Radiation-Resistant Hybrid Lotus Effect for Achieving Photoelectrocatalytic Self-Cleaning Anticontamination Coatings; 23) Improved, Low-Stress Economical Submerged Pipeline; 24) Optical Fiber Array Assemblies for Space Flight on the Lunar Reconnaissance Orbiter; 25) Local Leak Detection and Health Monitoring of Pressurized Tanks; 26) Dielectric Covered Planar Antennas at Submillimeter Wavelengths for Terahertz Imaging; 27) Automated Cryocooler Monitor and Control System; 28) Broadband Achromatic Phase Shifter for a Nulling Interferometer; 29) Super Dwarf Wheat for Growth in Confined Spaces; 30) Fine Guidance Sensing for Coronagraphic Observatories; 31) Single-Antenna Temperature- and Humidity-Sounding Microwave Receiver; 32) Multi-Wavelength, Multi-Beam, and Polarization-Sensitive Laser Transmitter for Surface Mapping; 33) Optical Communications Link to Airborne Transceiver; 34) Ascent Heating Thermal Analysis on Spacecraft Adaptor Fairings; 35) Entanglement in Self-Supervised Dynamics; 36) Prioritized LT Codes; 37) Fast Image Texture Classification Using Decision Trees; 38) Constraint Embedding Technique for Multibody System Dynamics; 39) Improved Systematic Pointing Error Model for the DSN Antennas; 40) Observability and Estimation of Distributed Space Systems via Local Information-Exchange Networks; 41) More-Accurate Model of Flows in Rocket Injectors; 42) In-Orbit Instrument-Pointing Calibration Using the Moon as a Target; 43) Reliability of Ceramic Column Grid Array Interconnect Packages Under Extreme Temperatures; 44) Six Degrees-of-Freedom Ascent Control for Small-Body Touch and Go; and 45) Optical-Path-Difference Linear Mechanism for the Panchromatic Fourier Transform Spectrometer.

Source record↗
DOE OSTI2020

Polar coupling enabled nonlinear optical filtering at MoS 2 /ferroelectric heterointerfaces

Complex oxide heterointerfaces and van der Waals heterostructures present two versatile but intrinsically different platforms for exploring emergent quantum phenomena and designing new functionalities. The rich opportunity offered by the synergy between these two classes of materials, however, is yet to be charted. Here, we report an unconventional nonlinear optical filtering effect resulting from the interfacial polar alignment between monolayer MoS 2 and a neighboring ferroelectric oxide thin film. The second harmonic generation response at the heterointerface is either substantially enhanced or almost entirely quenched by an underlying ferroelectric domain wall depending on its chirality, and can be further tailored by the polar domains. Unlike the extensively studied coupling mechanisms driven by charge, spin, and lattice, the interfacial tailoring effect is solely mediated by the polar symmetry, as well explained via our density functional theory calculations, pointing to a new material strategy for the functional design of nanoscale reconfigurable optical applications.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Coupling buried etalon layers to an engraved metasurface for durable and large-aperture meta-optics

Many optical applications that could potentially benefit from the design flexibility provided by the metasurface approach are being prohibited by the limited scalability of the fabrication and the robustness of the end-result structures when using a resonant meta-elements-based approach. In this study, an alternative demonstrated approach with superior scalability and robustness is substrate-engraved metasurfaces, based on medium mixing homogenization, yet it suffers from very limited optical response. Here we propose advancing this approach by coupling the metasurface with buried etalon layers, leading to enhancement in the optical response. A transfer matrix analysis is used to study the parameter space, predicting that the patterned reflectance values range of a beam shaper could be raised from only 4% to 30% when the metasurface is engraved in silica, and even up to 66% when engraved into higher-index oxides. Using the method proposed here, the phase difference range across the metasurface could be increased by 0.4 radians beyond the range achievable by a metasurface engraved in silica and could reach even higher values when embedded in higher-index materials. Full-wave numerical simulations are used to demonstrate a cylindrical metareflector and a metalens, further validating the analysis.

47 OTHER INSTRUMENTATION↗
NASA NTRS1981

Planar Rowland spectrometer for fiber-optic wavelength demultiplexing

A planar Rowland spectrometer was fabricated and characterized as a wavelength demultiplexer for multimode fiber-optic applications. The spectrometer consisted of a planar multimode glass waveguide with two curved end faces and a cylindrical concave attached to one of the end faces. Semiconductor lasers with wavelengths between 0.825 and 0.845 micron were used for the measurements. Cross-talk isolation between two adjacent fibers with center-to-center separation of 175 microns (100 A in wavelength difference) was measured to be 18 dB. The device's performance was limited by grating diffraction efficiency, optical aberration, waveguide dispersion, and waveguide losses.

Yen, H. W.↗
DOE OSTI2022

Recent Advances in 3D Printed Sensors: Materials, Design, and Manufacturing

Sensors are of great importance in different aspects of research and industry. Future sensors will require high-efficient and low-cost manufacturing, as well as high-performance functionality in areas, such as mechanical sensing, biomedical, and optical applications. Recent advances in 3D printing open a new paradigm for sensors fabrication as a precision, customizable, and seamless process. Here, in this article, the state-of-the-art 3D printing methods in sensors manufacturing is reviewed and the performance of the 3D printed sensing materials and devices is summarized. Special attention is paid to emerging multimaterial printing and 4D printing technologies, which will benefit the fabrication of a new generation of structures with multifunctionalities. The content on 3D printed sensors covers piezoelectric sensors, medical, and optical sensing devices. The performance of 3D printed sensors in comparison with the sensors made by traditional manufacturing is also covered. Finally, section 4 provides the viewpoints on the future development of 3D printed sensors.

36 MATERIALS SCIENCE↗
NASA NTRS2006

Optically Driven Deformable Mirrors

Optically driven deformable mirrors may eventually supplant electrically driven deformable mirrors in some adaptive-optics and active-optics applications. Traditionally, the mirror facets in electrically driven deformable mirrors are actuated, variously, by means of piezoelectric, electrostrictive, microelectromechanical, liquid-crystal, or thermal devices. At least one such device must be dedicated to each facet, and there must be at least one wire carrying a control or drive signal to the device. If a deformable mirror comprises many (e.g., thousands) of facets, then wiring becomes a major problem for design, and the problem is compounded in cases of piezoelectric or other actuators for which high drive voltages are required. In contrast, in optically driven mirrors, the wiring problem is eliminated. The basic principle of actuation of an optically driven deformable mirror is to use a laser beam to actuate a material. For example, a laser beam can be used to heat a material to make the material thermally expand to displace a mirror facet. In an experiment to demonstrate this principle, the actuator was a Golay cell having a diameter of approximately equal to 6 mm and a length of approximately equal to 10 mm. The beam from a laser diode was aimed at an absorber in the cell, thereby heating the gas in the cell. A mirror mounted on a 12.5-micron-thick polyethylene terephthalate diaphragm at one end of the cell became displaced as the gas expanded against the diaphragm. In one representative pair of experiments at a laser beam power of 0.23 W, the beam was mechanically chopped at frequencies of 1 and 5 Hz. The mirror exhibited corresponding oscillating displacements having amplitudes of 373 and 83 micron, respectively

Hemmati, Hamid↗
DOE OSTI2022

Quantum Photon Sources in WSe 2 Monolayers Induced by Weakly Localized Strain Fields

Quantum emitters in semiconductor transition metal dichalcogenide (TMD) monolayers hold great promise for many quantum optics applications due to the intriguing properties afforded by the host materials. The creation of localized excitonic states in two-dimensional semiconductors is also fundamentally interesting. Local strain engineering of TMD monolayers has been attested to be a viable approach for creating quantum emitters. However, despite the ubiquitous existence of local topography variations in the structures used to create strain gradients in the TMD monolayers, an understanding of their influence on the strain fields and exciton trapping is notably lacking, especially on the nanoscale. In this study, we investigate WSe 2 monolayers deposited on the edges of asfabricated trenches, which are deemed to induce 1D delocalized strain profiles in the monolayers, and observe optical signatures of weakly confined excitonic states supporting biexciton emission. Here, our numerical simulations of the strain distributions suggest that the quantum emitters originate from quasi-1D like localized strain profiles induced by local topography variations at the trench edges. These findings have strong implications toward the controlled creation of quantum emitters in TMD monolayers and their efficient coupling to photonic structures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Cs X Si 15 P 21 ( X = Sn or Pb): Polar Noncentrosymmetric Si–P Frameworks Stabilized by Covalent X –P Bonding

Metal silicon phosphides composed of earth-abundant Si and P tend to exhibit semiconducting properties and adopt diverse crystal structures with relatively small additions of structure-directing elements. The potential of silicon phosphide materials in nonlinear optical applications has been hindered by the inability to systematically produce noncentrosymmetric structures with such a flexible framework. Here, in this work, two isostructural compounds with a novel noncentrosymmetric structure were made possible by the inclusion of elements with stereochemically active lone pairs (Sn 2+ and Pb 2+ ). The structures were determined through single-crystal and synchrotron powder X-ray diffraction. Analysis of chemical bonding in real space through the electron localization function revealed stereochemically active Pb 2+ and Sn 2+ species in a trigonal pyramidal coordination with {Pb/Sn}–P bonds. Such covalent bonding between Pb and P is quite uncommon in extended solids and has been reported in a few rare instances. Band structure calculations and linear optical measurements confirm the semiconducting nature of Cs X Si 15 P 21 ( X = Sn or Pb). The synthesis was optimized to yield high-purity polycrystalline samples. The nonlinear optical properties show promising second-harmonic generation (SHG) coefficients from the Kurtz–Perry method. First-principles calculations of the nonlinear optical properties support the experimentally determined SHG values and provide moderate values of birefringence, suggesting Cs X Si 15 P 21 could be phase-matchable and practical nonlinear optical materials in the mid-IR region.

crystal structure↗
NASA NTRS1980

Study of fiber optics standardization, reliability, and applications

The use of fiber optics in space applications is investigated. Manufacturers and users detailed the problems they were having with the use or manufacture of fiber optic components. The general consensus of all the companies/agencies interviewed is that fiber optics is a maturing technology and will definitely have a place in future NASA system designs. The use of fiber optics was found to have two main advantages - weight savings and increased bandwidth.

Source record↗
DOE OSTI2022

A Generalizable Approach to Direct the Self-Assembly of Functional Blue-Phase Liquid Crystals

Blue phases (BPs) are soft and stimuli-responsive photonic crystals that are interesting for sensing, display, and lasing applications. Polycrystallinity has, however, limited both the study and applicability of BPs. Continuum simulations, which lack molecule-specific details, predict that striped chemical patterns, consisting of alternating homeotropic and planar regions, can be used to nucleate single crystals of BPs. Here it is experimentally demonstrated that, independent of the chemistry and complexity of the BP forming material, chemical patterns direct the self-assembly of BPs; these results indicate that a general, thermodynamics-based continuum description of BP self-assembly is adequate for a broad range of materials. When the pattern periodicity equals the BPII unit cell size, single crystals with (100) orientation form for all studied materials. Chemical patterns also promote the growth of BPI crystals with (110) orientation. Importantly, the self-assembly of a photopolymerizable BP is directed and thermally stable, UV-polymerized single crystals are prepared. As a result, the ability to create arbitrarily large, polymeric photonic single crystals with uniform lattice orientation, may have broad implications for optical applications.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Contracted, Not Converted: Photoluminescence Thermochromism in Ultrabright Pure Blue Emissive Hybrid Copper(I) Halide

Thermochromic luminescent materials are promising for applications such as sensors or display technologies. Understanding the mechanism of thermochromic luminescence in these materials plays an important role for their targeted applications. Here, a 0D copper(I) halide (TMP)2CuBr3 and 1D (TMP)Ag2Br3 (TMP = tetramethylphosphonium) are reported. While (TMP)Ag2Br3 is a weak light emitter, (TMP)2CuBr3 demonstrates ultrabright pure blue emission with photoluminescence (PL) quantum yield exceeding 90% within the temperature range 300–80 K. The emission in (TMP)2CuBr3 is attributed to the radiative recombination of self-trapped excitons (STEs) that arise localized on [CuBr3]2− anions. (TMP)2CuBr3 demonstrates excitation-selective PL thermochromism at low temperatures. In the literature, the origin of multiple STEs is often unclear in luminescent metal halides. Here, a detailed temperature-dependent spectroscopic and structural analysis suggests that the PL thermochromism in (TMP)2CuBr3 is associated with the appearance of a second STE state. The appearance of second STE is expected to have a structural origin, and it may be associated with the observed anomaly in thermal contraction near 200 K. The distinct PL features of melt-processible (TMP)2CuBr3 coupled with its remarkable photo- and thermal stability allow its consideration for practical optical applications, including temperature sensing.

Popy, Dilruba [University of Oklahoma, Norman]↗
DOE OSTI2021

Mechanisms for long carrier lifetime in Cd(Se)Te double heterostructures

II–VI semiconductors are used in numerous electro-optical applications. For example, CdTe-based solar technology is cost competitive with other electricity generation sources, yet there is still significant room to improve. Carrier lifetime has historically been well below the radiative recombination limit. Lifetimes reaching beyond 100 ns can significantly enhance performance and enable novel device structures. Here, double heterostructures (DHs) with passivated interfaces demonstrate lifetimes exceeding 1 µs, yet this appears only for CdSeTe and not for CdTe DHs. We compare the passivation mechanisms in CdTe and CdSeTe DHs. CdSeTe lifetimes on the order of 1 µs correspond to a combination of superior intragrain lifetime, extremely low grain boundary recombination and greater Te4+ interfacial presence compared to CdTe.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Cubic Crystal Structure Formation and Optical Properties within the Ag–B II –M IV –X (B II = Sr, Pb; M IV = Si, Ge, Sn; X = S, Se) Family of Semiconductors

Quaternary chalcogenide semiconductors are promising materials for energy conversion and nonlinear optical applications, with properties tunable primarily by varying the elemental composition and crystal structure. Here, we first analyze the connections among several cubic crystal structure types, as well as the orthorhombic Ag 2 PbGeS 4 -type structure, reported for select members within the Ag–B II –M IV –X (B II = Sr, Pb; M IV = Si, Ge, Sn; X = S, Se) compositional space. Focusing on the Ag–Pb–Si–S and Ag–Sr–Sn–S systems, we show that one structure type, with the formulas Ag 2 Pb 3 Si 2 S 8 and Ag 2 Sr 3 Sn 2 S 8 , is favored. We have prepared powder and single-crystal samples of Ag 2 Pb 3 Si 2 S 8 and Ag 2 Sr 3 Sn 2 S 8 , showing that each takes on the noncentrosymmetric cubic space group I$\bar{43}$d and is isostructural to the previously reported compound Ag 2 Sr 3 Ge 2 Se 8 . Through hybrid density functional theory calculations, these cubic compounds are demonstrated to be (quasi-)direct band gap semiconductors with high densities of states at the band maxima. Furthermore, the band-gap energies are measured by reflectance spectroscopy as 1.95(3) and 2.66(4) eV for Ag 2 Pb 3 Si 2 S 8 and Ag 2 Sr 3 Sn 2 S 8 , respectively. We further measure the optical properties and show the electronic band structures of three other isostructural A I –B II –M IV –X-type materials, i.e., Ag 2 Sr 3 Si 2 S 8 , Ag 2 Sr 3 Ge 2 S 8 , and Ag 2 Sr 3 Ge 2 Se 8 , showing that the band gaps can be predictably tuned by element substitution. Detailed visual analyses of the different structures and of their relationships with other members of the Ag–B II –M IV –X compositional family provide a basis for a broader understanding of the structure formation and optoelectronic properties within the quaternary chalcogenide semiconductor family.

14 SOLAR ENERGY↗
DOE OSTI2020

Chirality-Dependent Second Harmonic Generation of MoS 2 Nanoscroll with Enhanced Efficiency

Materials with high second harmonic generation (SHG) efficiency and reduced dimensions are favorable for integrated photonics and nonlinear optical applications. Here, we fabricate MoS 2 nanoscrolls with different chiralities and study their SHG performances. As a 1D material, MoS 2 nanoscroll shows reduced symmetry and strong chirality dependency in the polarization-resolved SHG characterizations. This SHG performance can be well explained by the superposition theory of second harmonic field of the nanoscroll walls. MoS 2 nanoscrolls with certain chiralities and diameters in our experiment can have SHG intensity up to 95 times stronger than that of monolayer MoS 2 , and the full potential can still be further exploited. The same chirality-dependent SHG can be expected for nanoscrolls or nanotubes composed of other noncentrosymmetric 2D materials, such as WS 2 , WSe 2 , and hBN. Here, the characterization and analysis results presented here can also be exploited as a nondestructive technique to determine the chiralities of these nanoscrolls and nanotubes.

42 ENGINEERING↗
DOE OSTI2025

V‐Groove Si Nanopatterning for the Direct Epitaxy of Orientation‐Patterned III–V Nonlinear Optical Crystals

Orientation‐patterned (OP) III–V semiconductors—used as quasi‐phase‐matched crystals for nonlinear optics applications—are typically epitaxially grown on expensive III–V substrates using a complex process requiring three separate epitaxy steps. In this work, a method is demonstrated for growing orientation‐patterned III–V crystals on Si substrates through V‐groove nanopatterning and a single epitaxial growth. V‐groove Si allows for suppression of random antiphase domain formation that is typical of III–V growth on (001)‐oriented Si through the use of (111)‐faceted trenches patterned on (001)‐oriented Si substrates. By alternating the directions of the V‐groove trenches between [110] and [10], antiphase boundaries can be selectively induced at the boundaries between the two directions of trenches due to the difference in symmetry between the III–V material and Si. This approach allows for a greatly simplified process for growing OP‐III‐Vs and more broadly is a new, robust approach for precisely patterning antiphase boundaries of arbitrary shape and length scales down to 50 nm.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2026

Decoding THz‐Driven Dynamic Fingerprints of Ferroelectric Nanotwin Networks

Ultrafast polarization dynamics in ferroelectrics are of considerable interest for high-speed tunable dielectrics and electro-optics. Extended domain wall networks formed in ferroelectric twin nanodomains can support collective dynamics in the terahertz regime but require techniques that track polarization and strain evolution driven by ultrafast stimulus. Here, we use multi-modal probing of THz-pulse-driven excitations in PbTiO 3 /SrTiO 3 superlattices by combining X-ray free electron laser measurements that directly tracks lattice changes, with optical second harmonic generation that tracks the electronic potential coupled with the lattice potential. Dynamical phase-field modeling enables fingerprinting of these collective modes as superpositions of domain “breathing” through wall oscillations and polarization “rotations” with still walls. Ultrafast domain wall motion at 0.1–0.5 THz is observed at practical fields of 100 kV/cm with wall velocities of >4000 m/s, approaching typical speed of sound in PbTiO 3 . A unique “charging” mode is discovered that can electrically charge and discharge domain walls on ∼4 ps time scale thus dynamically tuning wall conductivity. Integrated experimental and theoretical fingerprinting of the dynamical landscape presented here enables ultrafast control of ferroics for high-speed microelectronics and optical applications.

THz dynamics↗
DOE OSTI2021

Assembly of Close–Packed Ferroelectric Polymer Nanowires via Interface–Epitaxy with ReS 2

The flexible, transparent, and low-weight nature of ferroelectric polymers makes them promising for wearable electronic and optical applications. To reach the full potential of the polarization-enabled device functionalities, large-scale fabrication of polymer thin films with well-controlled polar directions is called for, which remains a central challenge. The widely exploited Langmuir–Blodgett, spin-coating, and electrospinning methods only yield polymorphous or polycrystalline films, where the net polarization is compromised. Here, an easily scalable approach is reported to achieve poly(vinylidene fluoride-trifluoroethylene) P(VDF-TrFE) thin films composed of close-packed crystalline nanowires via interface-epitaxy with 1T'-ReS 2 . Upon controlled thermal treatment, uniform P(VDF-TrFE) films restructure into about 10 and 35 nm-wide (010)-oriented nanowires that are crystallographically aligned with the underlying ReS 2 , as revealed by high-resolution transmission electron microscopy. Piezoresponse force microscopy studies confirm the out-of-plane polar axis of the nanowire films and reveal coercive voltages as low as 0.1 V. Reversing the polarization can induce a conductance switching ratio of >10 8 in bilayer ReS 2 , over six orders of magnitude higher than that achieved by an untreated polymer gate. Lastly, this study points to a cost-effective route to large-scale processing of high-performance ferroelectric polymer thin films for flexible energy-efficient nanoelectronics.

crystalline nanowires↗