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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Cloud Physics Lidar Optical Measurements During the SAFARI-2000 Field Campaign

In this presentation, we will show new optical data processing results from the Cloud Physics War during SAFARI-2000. Retrieved products include aerosol and cloud layer location and identification, layer optical depths, vertical extinction profiles, and extinction-to-backscatter (S) ratios for 532 and 1064 nm. The retrievals will focus on the persistent and smoky planetary boundary layer and occasional elevated aerosol layers found in southern Africa during August and September 2000.

Hlavka, Dennis L.↗
NASA NTRS2004

Three-Dimensional High-Resolution Optical/X-Ray Stereoscopic Tracking Velocimetry

Measurement of three-dimensional (3-D) three-component velocity fields is of great importance in a variety of research and industrial applications for understanding materials processing, fluid physics, and strain/displacement measurements. The 3-D experiments in these fields most likely inhibit the use of conventional techniques, which are based only on planar and optically-transparent-field observation. Here, we briefly review the current status of 3-D diagnostics for motion/velocity detection, for both optical and x-ray systems. As an initial step for providing 3-D capabilities, we nave developed stereoscopic tracking velocimetry (STV) to measure 3-D flow/deformation through optical observation. The STV is advantageous in system simplicity, for continually observing 3- D phenomena in near real-time. In an effort to enhance the data processing through automation and to avoid the confusion in tracking numerous markers or particles, artificial neural networks are employed to incorporate human intelligence. Our initial optical investigations have proven the STV to be a very viable candidate for reliably measuring 3-D flow motions. With previous activities are focused on improving the processing efficiency, overall accuracy, and automation based on the optical system, the current efforts is directed to the concurrent expansion to the x-ray system for broader experimental applications.

Cha, Soyoung S.↗
NASA NTRS2005

Three-Dimensional High-Resolution Optical/X-Ray Stereoscopic Tracking Velocimetry

Measurement of three-dimensional (3-D) three-component velocity fields is of great importance in a variety of research and industrial applications for understanding materials processing, fluid physics, and strain/displacement measurements. The 3-D experiments in these fields most likely inhibit the use of conventional techniques, which are based only on planar and optically-transparent-field observation. Here, we briefly review the current status of 3-D diagnostics for motion/velocity detection, for both optical and x-ray systems. As an initial step for providing 3-D capabilities, we have developed stereoscopic tracking velocimetry (STV) to measure 3-D flow/deformation through optical observation. The STV is advantageous in system simplicity, for continually observing 3-D phenomena in near real-time. In an effort to enhance the data processing through automation and to avoid the confusion in tracking numerous markers or particles, artificial neural networks are employed to incorporate human intelligence. Our initial optical investigations have proven the STV to be a very viable candidate for reliably measuring 3-D flow motions. With previous activities focused on improving the processing efficiency, overall accuracy, and automation based on the optical system, the current efforts is directed to the concurrent expansion to the x-ray system for broader experimental applications.

Cha, Soyoung S.↗
DOE OSTI2020

Multiple Tunable Hyperbolic Resonances in Broadband Infrared Carbon-Nanotube Metamaterials

Aligned densely packed carbon-nanotube metamaterials prepared using vacuum filtration are an emerging infrared nanophotonic material. We report multiple hyperbolic plasmon resonances, together spanning the mid-infrared, in individual resonators made from aligned and densely packed carbon nanotubes. In a near-field scanning optical microscopy (NSOM) imaging study of nanotube metamaterial resonators, we observe distinct deeply subwavelength field profiles at the fundamental and higher-order resonant frequencies. The wafer-scale area of the nanotube metamaterials allows us to combine this near-field imaging with a systematic far-field spectroscopic study of the scaling properties of many resonator arrays. Thorough theoretical modeling agrees with these measurements and identifies the resonances as higher-order Fabry-Perot (FP) resonances of hyperbolic waveguide modes. Nanotube resonator arrays show broadband extinction from 1.5–10 µm and reversibly switchable extinction in the 3–5 µm atmospheric transparency window through the coexistence of multiple modes in individual ribbons. Broadband carbon-nanotube metamaterials supporting multiple resonant modes are a promising candidate for ultracompact absorbers, tunable thermal emitters, and broadband sensors in the mid-infrared.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Optical Particle Measurements during EPCAPE Field Campaign Report

This campaign requested the deployment of the U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) User Facility optical particle counter (OPC) at the first ARM Mobile Facility (AMF1) located at the Scripps Pier in La Jolla, California during the Eastern Pacific Cloud Aerosol Precipitation Experiment (EPCAPE). The addition of the OPC was requested for two reasons. (1) Close the gap between the scanning mobility particle sizer (SMPS) and aerodynamic particle sizer (APS) size distribution from the Aerosol Observing System (AOS) measurements. (2) Principal investigator Petters has been working with Tracking Aerosol Convection Interaction Experiment (TRACER) data to compute particle fluxes from Doppler lidar (Petters et al. 2024). Briefly, backscatter flux is obtained using the eddy covariance technique using the Doppler vertical velocity and attenuated backscatter. Building upon prior studies, we were able to relate backscatter to particle number concentration by calibrating the lidar retrievals against optical particle counter-measured ground-based aerosol size distribution and radiosonde-interpolated relative humidity at lidar sample height. Performing similar analysis was of interest to EPCAPE to better understand the emissions and vertical transport of large particles into the overlying stratus clouds. However, as stated above, this analysis requires an optical size distribution that covers the 0.3-30-μm-diameter size range. The OPC was deployed between 2023-04-14 and 2024-02-14. The deployment, data quality analysis, and data archiving was handled by the DOE ARM instrument mentor team without additional involvement by the principal investigator. Data quality was marked as “routine” for the majority of the campaign.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1994

Optical studies of gamma-ray burst fields. 3: GRB 790613 and GRB 781124

An optical photometric and proper motion study of the fields of the gamma-ray bursts GRB 790613 and GRB 781124 is presented. No objects were visible on our Charge Coupled Devices (CCD) images inside the GRB 790613 error box. About 15 objects are visible on our CCD images inside the GRB 781124 error box. Two of these objects were found to be faint galaxies. Two stars with sizeable proper motions were identified near, but outside of the GRB 781124 error box. No large proper motion objects were found in the area surrounding the GRB 790613 error box.

Harrison, Thomas E.↗
NASA NTRS1986

Optical system design, analysis, and production for advanced technology systems; Proceedings of the Meeting, Innsbruck, Austria, Apr. 15-17, 1986

The present conference considers topics in the fields of optical systems design software, the design and analysis of optical systems, illustrative cases of advanced optical system design, the integration of optical designs into greater systems, and optical fabrication and testing techniques. Attention is given to an extended range diffraction-based merit function for lens design optimization, an assessment of technologies for stray light control and evaluation, the automated characterization of IR systems' spatial resolution, a spectrum of design techniques based on aberration theory, a three-field IR telescope, a large aperture zoom lens for 16-mm motion picture cameras, and the use of concave holographic gratings as monochomators. Also discussed are the use of aspherics in optical systems, glass choice procedures for periscope design, the fabrication and testing of unconventional optics, low mass mirrors for large optics, and the diamond grinding of optical surfaces on aspheric lens molds.

Fischer, Robert E.↗
NASA NTRS2015

Optical Characterization of Component Wear and Near-Field Plasma of the Hermes Thruster

Optical emission spectral (OES) data are presented which correlate trends in sputtered species and the near-field plasma with the Hall-Effect Rocket with Magnetic Shielding (HERMeS) thruster operating condition. The relative density of singly-ionized xenon (Xe II) is estimated using a collisional-radiative model. OES data were collected at three radial and several axial locations downstream of the thruster's exit plane. These data were deconvolved to show the structure for the near-field plasma as a function of thruster operating condition. The magnetic field is shown to have a much greater affect on plasma structure than the discharge voltage with the primary ionization/acceleration zone boundary being similar for all nominal operating voltages at constant power. OES measurement of sputtered boron shows that the HERMeS thruster is magnetically shielded across its operating envelope. Preliminary assessment of carbon sputtered from the keeper face suggest it increases significantly with operating voltage, but the uncertainty associated with these measurements is very high.

Electric Propulsion↗
NASA NTRS1987

KC-135 aero-optical turbulent boundary layer/shear layer experiment revisited

The aero-optical effects associated with propagating a laser beam through both an aircraft turbulent boundary layer and artificially generated shear layers are examined. The data present comparisons from observed optical performance with those inferred from aerodynamic measurements of unsteady density and correlation lengths within the same random flow fields. Using optical instrumentation with tens of microsecond temporal resolution through a finite aperture, optical performance degradation was determined and contrasted with the infinite aperture time averaged aerodynamic measurement. In addition, the optical data were artificially clipped to compare to theoretical scaling calculations. Optical instrumentation consisted of a custom Q switched Nd:Yag double pulsed laser, and a holographic camera which recorded the random flow field in a double pass, double pulse mode. Aerodynamic parameters were measured using hot film anemometer probes and a five hole pressure probe. Each technique is described with its associated theoretical basis for comparison. The effects of finite aperture and spatial and temporal frequencies of the random flow are considered.

Craig, J.↗
NASA NTRS1988

Calculating Optical-Transmitter Radiation Pattern s

New formula gives more-accurate gains and pointing losses. Set of approximate formulas predicts angular dependence of far radiation field coherent optical transmitter, telescope having central obscuring disk. Formulas derived without recourse to simplifying assumption of uniform plane-wave illumination used to derive less-accurate traditional formulas.

Marshall, William K.↗
NASA NTRS1991

Fiber optic and laser sensors IX; Proceedings of the Meeting, Boston, MA, Sept. 3-5, 1991

The present volume on fiber-optic and laser sensors discusses industrial applications of fiber-optic sensors, fiber-optic temperature sensors, fiber-optic current sensors, fiber-optic pressure/displacement/vibration sensors, and generic fiber-optic systems. Attention is given to a fiber-sensor design for turbine engines, fiber-optic remote Fourier transform IR spectroscopy, near-IR fiber-optic temperature sensors, and an intensity-type fiber-optic electric current sensor. Topics addressed include fiber-optic magnetic field sensors based on the Faraday effect in new materials, diaphragm size and sensitivity for fiber-optic pressure sensors, a microbend pressure sensor for high-temperature environments, and linear position sensing by light exchange between two lossy waveguides. Also discussed are two-mode elliptical-core fiber sensors for measurement of strain and temperature, a fiber-optic interferometric X-ray dosimeter, fiber-optic interferometric sensors using multimode fibers, and optical fiber sensing of corona discharges.

Depaula, Ramon P.↗
NASA NTRS1987

Fiber optic and laser sensors IV; Proceedings of the Meeting, Cambridge, MA, Sept. 22-24, 1986

The conference presents papers on industrial uses of fiber optic sensors, point and distributed polarimetric optical fiber sensors, fiber optic electric field sensor technology, micromachined resonant structures, single-mode fibers for sensing applications, and measurement techniques for magnetic field gradient detection. Consideration is also given to electric field meter and temperature measurement techniques for the power industry, the calibration of high-temperature fiber-optic microbend pressure transducers, and interferometric sensors for dc measurands. Other topics include the recognition of colors and collision avoidance in robotics using optical fiber sensors, the loss compensation of intensity-modulating fiber-optic sensors, and an embedded optical fiber strain tensor for composite structure applications.

De Paula, Ramon P.↗
NASA NTRS2018

Optical Measurement System for Strain Field Ahead of a Crack Tip for Lattice Structures

The aim of the ARAMADAS project is to automate the construction of cuboctahedral lattice structures. Lattice materials are appealing for aerospace applications due to their strength and stiffness at ultra-light densities. However, in order for any material to be realistically considered for such environments, it must also be damage tolerant. The ability of a material to absorb damage is characterized by its fracture toughness, which remains poorly characterized for lattice materials. Consequently, the objective of this research is to develop an optical measurement system to experimentally validate the strain field ahead of a crack tip in architecture lattice materials. Although the ability to predict the strain field ahead of a crack tip has been investigated for continuum materials, such behaviour of three-dimensional architectures is under-investigated. As such, we will use a custom optical measurement system to track deformation of the voxels in a side-cracked plate fracture specimen. The system shall use 3D pose estimation, stereo imaging, and possibly color tracking, in combination with optical flow algorithms, to compute information regarding the three-dimensional movement movement of the lattice nodes during mechanical testing. Bench top experiments will validate the optical measurement system and characterize precision. Additionally, the effect of multiple cameras on precision, as well as system scalability will be investigated. Final results will compare measured lattice deformation with finite element predictions.

Lennig, Miriam↗
DOE OSTI2023

Exciton–Polaritons in CsPbBr 3 Crystals Revealed by Optical Reflectivity in High Magnetic Fields and Two-Photon Spectroscopy

Cesium lead bromide (CsPbBr3) is a representative material of the emerging class of lead halide perovskite semiconductors that possess remarkable optoelectronic properties. Its optical properties in the vicinity of the bandgap energy are greatly contributed by excitons, which form exciton polaritons due to strong light–matter interactions. Exciton–polaritons in solution-grown CsPbBr 3 crystals are examined by means of circularly polarized reflection spectroscopy measured in high magnetic fields up to 60 T. The excited 2P exciton state is measured by two-photon absorption. Comprehensive modeling and analysis provides detailed quantitative information about the exciton–polariton parameters: exciton binding energy of 32.5 meV, oscillator strength characterized by longitudinal–transverse splitting of 5.3 meV, damping of 6.7 meV, reduced exciton mass of 0.18$m$ 0 , exciton diamagnetic shift of 1.6 μeV T -2 , and exciton Landé factor $g$ x = + 2.35. It is shown that the exciton states can be described within a hydrogen-like model with an effective dielectric constant of 8.7. From the measured exciton longitudinal–transverse splitting, Kane energy of E p = 15 eV is evaluated, which is in reasonable agreement with values of 11.8–12.5 eV derived from the carrier effective masses.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Numerical Analysis of Radiation Effects on Fiber Optic Sensors

Optical fiber sensors (OFS) are a potential candidate for monitoring physical parameters in nuclear environments. However, under an irradiation field the optical response of the OFS is modified via three primary mechanisms: (i) radiation-induced attenuation (RIA), (ii) radiation-induced emission (RIE), and (iii) radiation-induced compaction (RIC). For resonance-based sensors, RIC plays a significant role in modifying their performance characteristics. In this paper, we numerically investigate independently the effects of RIC and RIA on three types of OFS widely considered for radiation environments: fiber Bragg grating (FBG), long-period grating (LPG), and Fabry-Perot (F-P) sensors. In our RIC modeling, experimentally calculated refractive index (RI) changes due to low-dose radiation are extrapolated using a power law to calculate density changes at high doses. The changes in RI and length are subsequently calculated using the Lorentz–Lorenz relation and an established empirical equation, respectively. The effects of both the change in the RI and length contraction on OFS are modeled for both low and high doses using FIMMWAVE, a commercially available vectorial mode solver. An in-depth understanding of how radiation affects OFS may reveal various potential OFS applications in several types of radiation environments, such as nuclear reactors or in space.

42 ENGINEERING↗
NASA NTRS1992

An optical study of grain formation: Casting and solidification technology (2-IML-1)

By studying the unidirectional growth of a metal-model material in microgravity, an attempt is made to characterize alloy solidification. Using holograms and supporting temperature measurements obtained during processing in the Fluids Experiment System (FES), the solute and thermal fields associated with the dendrite growth front and extraneous nucleation will be measured and compared to a theoretical (computational) model. Ground based supporting experiments include particle tracking to measure the velocity fields, and optical phase shift techniques (confocal optical signal processing, interferometry, and Schlieren) to study thermal and solutal fields.

Mccay, Mary H.↗
DOE OSTI2020

Optical evidence of the chiral magnetic anomaly in the Weyl semimetal TaAs

Chiral pumping from optical electric fields oscillating at terahertz frequencies is observed in the Weyl material TaAs with electric and magnetic fields aligned along both the $\textit{a}$ and $\textit{c}$ axes. In this work, free-carrier spectral weight enhancement is measured directly, confirming theoretical expectations of chiral pumping. A departure from linear field dependence of the Drude weight is observed at the highest fields in the quantum limit, providing evidence of field-dependent Fermi velocity of the chiral Landau level. Implications for the chiral magnetic effect in Weyl semimetals from the optical $\textit{f}$-sum rule are discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Near-field imaging of plasmonic nanopatch antennas with integrated semiconductor quantum dots

Plasmonic nanopatch antennas that incorporate dielectric gaps hundreds of picometers to several nanometers thick have drawn increasing attention over the past decade because they confine electromagnetic fields to grossly sub-diffraction-limited volumes. Substantial control over the optical properties of excitons and color centers confined within these plasmonic cavities has already been demonstrated with far-field optical spectroscopies, but near-field optical spectroscopies are essential for an improved understanding of the plasmon–emitter interaction at the nanoscale. Here, we characterize the intensity and phase-resolved plasmonic response of isolated nanopatch antennas by cathodoluminescence microscopy. Furthermore, we explore the distinction between optical and electron beam spectroscopies of coupled plasmon–exciton heterostructures to identify constraints and opportunities for future nanoscale characterization and control of hybrid nanophotonic structures. While we observe substantial Purcell enhancement in time-resolved photoluminescence spectroscopies, negligible Purcell enhancement is observed in cathodoluminescence spectroscopies of hybrid nanophotonic structures. The substantial differences in measured Purcell enhancement for electron beam and laser excitation can be understood as a result of the different selection rules for these complementary experiments. Overall, these results provide a fundamentally new understanding of near-field plasmon–exciton interactions in nanopatch antennas, which is essential for myriad emerging quantum photonic devices.

36 MATERIALS SCIENCE↗