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Results for “Optical Probe”

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 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
NASA NTRS2018

A Long-Lived Neutron Star Merger Remnant in GW170817: Constraints and Clues from X-ray Observations

Multimessenger observations of GW170817 have not conclusively established whether the merger remnant is a black hole (BH) or a neutron star (NS). We show that a long-lived magnetized NS with a poloidal field B ≈ 1012 G is fully consistent with the electromagnetic dataset, when spin-down losses are dominated by gravitational wave (GW) emission. The required ellipticity ε >~ 10−5 can result from a toroidal magnetic field component much stronger than the poloidal component, a configuration expected from an NS newly formed from a merger. Abrupt magnetic dissipation of the toroidal component can lead to the appearance of X-ray flares, analogous to the one observed in gamma-ray burst (GRB) afterglows. In the X-ray afterglow of GW170817, we identify a low-significance (>~3σ) temporal feature at 155 d, consistent with a sudden reactivation of the central NS. Energy injection from the NS spin-down into the relativistic shock is negligible, and the underlying continuum is fully accounted for by a structured jet seen off-axis. Whereas radio and optical observations probe the interaction of this jet with the surrounding medium, observations at X-ray wavelengths, performed with adequate sampling, open a privileged window on to the merger remnant.

gravitational waves↗
NASA NTRSDate not supplied

Experimental and Computational Investigation of Valve Motion in a Resonant Pulse Combustor

The motion of a passive reed-type valve and a poppet-style valve operating in a small scale, liquid-fueled pulse combustor is investigated experimentally. Valve position and combustion chamber pressure are simultaneously measured using an in-house fabricated optical position probe. The reed valve configuration is found to operate in a self-aspirated mode, generating significant pressure gain. The poppet valve configuration cannot operate without forced air, and does not generate pressure gain. Both type valves are tested in combustors of multiple lengths. Close examination of the respective valve motions indicate that the reed valve is highly non-linear, with unique attributes that appear essential for self-aspiration. Dynamic models for the motion of each valve are implemented in a computational fluid dynamic (CFD) simulation of the pulse combustor in order to assess if this unique valve motion is critical to successful operation. The results show that it is. The implications of these results are discussed. The need for active actuation with feedback control, rather than passive valve actuation is highlighted as a critical technology for practical resonant pulse combustors.

Combustion↗
NASA NTRSDate not supplied

Experimental and Computational Investigation of Valve Motion in a Resonant Pulse Combustor

The motion of a passive reed-type valve and a poppet-style valve operating in a small scale, liquid-fueled pulse combustor is investigated experimentally. Valve position and combustion chamber pressure are simultaneously measured using an in-house fabricated optical position probe. The reed valve configuration is found to operate in a self-aspirated mode, generating significant pressure gain. The poppet valve configuration cannot operate without forced air, and does not generate pressure gain. Both type valves are tested in combustors of multiple lengths. Close examination of the respective valve motions indicate that the reed valve is highly non-linear, with unique attributes that appear essential for self-aspiration. Dynamic models for the motion of each valve are implemented in a computational fluid dynamic (CFD) simulation of the pulse combustor in order to assess if this unique valve motion is critical to successful operation. The results show that it is. The implications of these results are discussed. The need for active actuation with feedback control, rather than passive valve actuation is highlighted as a critical technology for practical resonant pulse combustors.

Combustion↗
NASA NTRS2026

Ice in Convective Storm Environments: Assessing Impacts of Microphysics on Simulated Reflectivities

Satellite radar retrievals of clouds and precipitation rely on assumptions about the microphysical properties of hydrometeors such as particle size distributions (PSDs) and massdimensional relationships, which have been shown to vary in distinct environments. A deeper understanding of linkages between mass-dimensional relationships, ice crystal shape, and radar reflectivities across cloud and precipitation regimes is necessary for developing new retrievals for upcoming satellite radar missions, including the INvestigation of Convective UpdraftS (INCUS), as well as future missions that will feature space-borne radars observing clouds, convection, and precipitation. This study investigates ice microphysical characteristics through aircraft in-situ and remote sensing observations from two convective events during the Mid-latitude Continental Convective Clouds Experiment (MC3E) in the Southern Great Plains, and tests implications for ice particle habit in forward modeled radar observations. During MC3E, the Ka/Ku- band High Altitude Imaging Wind and Rain Airborne Profiler (HIWRAP) was onboard the NASA ER-2 aircraft, while in-situ measurements were taken onboard the University of North Dakota Citation. In-situ PSDs and particle shape information from optical array probe data are used to forward model radar reflectivities from particle scattering databases and are compared against HIWRAP reflectivities. Various particle combinations can be used to find agreement with HIWRAP observations, and the forward modeled reflectivities were sensitive to particle type. Varying the riming on the aggregate and graupel particles resulted in larger than 10 dB differences in reflectivities. The in-situ and radar observations imply the occurrence of aggregation, size sorting and lofting particles.

Julia A. Shates↗
DOE OSTI2019

An End-to-end Deep Convolutional Neural Network for a Multi-scale Image Matching and Localization Problem

Abstract Diverse imaging techniques are utilized in many scientific domains to acquire a rich description of the subject under study and to further discover a variety of its proper- ties. Especially, in sample systems, by probing with optical, electron or x-ray beams, the captured images describe the sample in an extremely large range of length scales. This makes the correlation from one image to another very difficult in addition to the intrinsic appearance complexity of those scientific images. In this paper, we aim to tackle this multi-scale image matching and localization problem by proposing an end-to-end deep convolutional neural net- work. Our proposed network is designed to first generate different filters according to the two queried images originated from different length scales. Then, to compute the correlation map, we use these filters to predict the correspondence between the two images. For the training and evaluation, we collect a number of electron microscopy experiments to form a multi-scaled image patch dataset comprised of various material structures. We observe about 90% accuracy for multi-scale image matching and localization while a triplet-based network shows about 78% accuracy.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2019

Frequency-based detection of chemical expansion dynamics in thin films

Current techniques for measuring chemical expansion in thin film structures are too slow, too imprecise, or require synchrotrons. In contrast, nanoscale electrochemomechanical spectroscopy (NECS) can be used to make nanoscale measurements at time scales of seconds with simple contact or non-contact sensors. In a NECS measurement, a sample, such as thin-film oxide structure, is subjected to a temporally modulated stimulus, such as a sinusoidally alternating voltage. The stimulus causes the sample to expand, contract, deflect, or otherwise deform. A sensor, such as a contact probe or optical sensor, produces an electrical signal in response to this deformation that is correlated with the temporal modulation of the stimulus. Because the stimulus and deformation are correlated, the temporal modulation of the stimulus can be used to filter the deformation signal produced by the sensor, producing a precise, sensitive measurement of the deformation.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Imaging grain microstructure in a model ceramic energy material with optically generated coherent acoustic phonons

Characterization of microstructure, chemistry and function of advanced energy materials remains a challenge for instrumentation science with tremendous opportunity for new discoveries. This active area of research is starting to make considerable strides with examples ranging from methodologies that employ bright X-rays, electron microscopy and optical spectroscopy. However, further development of instruments, capable of multimodal measurements, is necessary to fully reveal complex microstructure evolution in realistic environments and dynamical systems that are far from equilibrium. In this regard, laser-based instruments have a unique advantage as multiple measurement methodologies are easily combined into a single instrument using standard optics. A new pump-probe method that uses optically generated acoustic phonons is expanding standard optical characterization by providing depth resolved information. Here we report on a noteworthy extension of this pump-probe method to image grain microstructure in ceria. Rich information regarding the orientation of individual crystallites is obtained by monitoring acoustic phonon velocities and noting how the polarization of the probe beam influences the detected signal amplitude. When paired with other optical microscopies, this methodology will provide new perspectives for optical characterization of ceramic materials.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Hybrid catadioptric system for advanced optical cavity velocimetry

A probe including reflector is disclosed to measure the velocity distribution of a moving surface along many lines of sight. Laser light, directed to the surface by the probe and then reflected back from the surface, is Doppler shifted by the moving surface, collected into probe, and then directed to detection equipment through optic fibers. The received light is mixed with reference laser light and using photonic Doppler velocimetry, a continuous time record of the surface movement is obtained. An array of single-mode optical fibers provides an optic signal to one or more lens groups and a reflector, such as a parabolic reflector having a mirrored interior surface.

36 MATERIALS SCIENCE↗
NASA NTRS2023

A Multi-Sensor, Low Volume, Automated Culture System for Space Biology Experiments

Optical density (absorbance) is commonly used in microbiology to measure cell concentration and other colorimetric indicators. It is the main type of bioscience data returned from the BioSentinel small spacecraft mission, which was recently launched as a secondary payload on Artemis I. The flight unit takes absorbance measurements of yeast cultures at 570 nm, 630 nm, and 850 nm to track cell concentration and oxidation-reduction (redox) state of the metabolic indicator dye alamarBlue over time [1]. Because the data returned from a small spacecraft mission is necessarily limited, BioSentinel uses a specialized ground-based experiment apparatus to map the absorbance data onto several other parameters. This culture apparatus is composed of a polycarbonate base and lid which contain ports for several commercial sensors, including a standard 12 mm dissolved oxygen probe, gaseous CO2, fluid pressure, and two micro-probes for measuring pH and redox potential. It also contains a pressure relief valve, a rubber membrane for culture interaction, and a 12mm port for the custom optical probe designed to match in-flight measurements. Modules in two corners expand the culture volume into narrow columns, enabling solid-state optical density measurement and dielectric spectroscopy. The apparatus can be fit to a plate for magnetic stirring. The apparatus’s optical probe allows mapping between the flight unit’s optical data and the additional parameters measured by the ground-based experiments. Within the probe, a linear actuator pulls a plunger, drawing culture volume into the optical path. The actuator then pushes out the plunger and culture volume, cleaning any stray yeast from the inside surface of the probe. The probe chassis is 3D-printed from biocompatible resin with the optoelectronics cured inside an optically clear conformal coat which functions as a lens. To optimize the probe’s dimensions, including optical path, a test harness was developed to manipulate and measure distance while the LED light sources and photodiode detector are in operation. The test harness was composed of two 3/64” thick polycarbonate plates mounted to a set of calipers. The LEDs and photodiode were mounted on the outside of each plate. A cuvette of sample fluid was then clamped between the plates in line between the LEDs and photodiode. The test harness generated a 78% signal change between water and a dye standard for the green (570 nm) LED, a 90% signal change for the red (630 nm) LED, and a 25% signal change between water and overgrown yeast for the infrared (850 nm) LED. The improvements to the ground experiment apparatus (culture volume reduction, inclusion of an optical probe to measure flight-like optical data, and magnetic stirring for culture homogeneity) allow for more flight-like measurements to be taken and more accurate mapping of these additional parameters to the optical data returned from the flight unit. This enhancement to mission science return will give insight into how deep space radiation may affect human biology for future long-term space exploration.

Multi-Sensor↗
DOE OSTI2022

Hyperspectral imaging of exciton confinement within a moiré unit cell with a subnanometer electron probe

Electronic and optical excitations in two-dimensional systems are distinctly sensitive to the presence of a moiré superlattice. Here we used cryogenic transmission electron microscopy and spectroscopy to simultaneously image the structural reconstruction and associated localization of the lowest-energy intralayer exciton in a rotationally aligned WS 2 -WSe 2 moiré superlattice. In conjunction with optical spectroscopy and ab initio calculations, we determined that the exciton center-of-mass wave function is confined to a radius of approximately 2 nanometers around the highest-energy stacking site in the moiré unit cell. Our results provide direct evidence that atomic reconstructions lead to the strongly confining moiré potentials and that engineering strain at the nanoscale will enable new types of excitonic lattices.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Campanile Near-Field Probes Fabricated by Nanoimprint Lithography on the Facet of an Optical Fiber

One of the major challenges to the widespread adoption of plasmonic and nano-optical devices in real-life applications is the difficulty to mass-fabricate nano-optical antennas in parallel and reproducible fashion, and the capability to precisely place nanoantennas into devices with nanometer-scale precision. In this study, we present a solution to this challenge using the state-of-the-art ultraviolet nanoimprint lithography (UV-NIL) to fabricate functional optical transformers onto the core of an optical fiber in a single step, mimicking the 'campanile' near-field probes. Imprinted probes were fabricated using a custom-built imprinter tool with co-axial alignment capability with sub < 100 nm position accuracy, followed by a metallization step. Scanning electron micrographs confirm high imprint fidelity and precision with a thin residual layer to facilitate efficient optical coupling between the fiber and the imprinted optical transformer. The imprinted optical transformer probe was used in an actual NSOM measurement performing hyperspectral photoluminescence mapping of standard fluorescent beads. The calibration scans confirmed that imprinted probes enable sub-diffraction limited imaging with a spatial resolution consistent with the gap size. This novel nano-fabrication approach promises a low-cost, high-throughput, and reproducible manufacturing of advanced nano-optical devices.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Reduced lattice thermal conductivity of Fe-bearing bridgmanite in Earth's deep mantle: Reduced Conductivity of Fe-Bridgmanite

Complex seismic, thermal, and chemical features have been reported in Earth's lowermost mantle. In particular, possible iron enrichments in the large low shear-wave velocity provinces (LLSVPs) could influence thermal transport properties of the constituting minerals in this region, altering the lower mantle dynamics and heat flux across core-mantle boundary (CMB). Thermal conductivity of bridgmanite is expected to partially control the thermal evolution and dynamics of Earth's lower mantle. Importantly, the pressure-induced lattice distortion and iron spin and valence states in bridgmanite could affect its lattice thermal conductivity, but these effects remain largely unknown. Here we precisely measured the lattice thermal conductivity of Fe-bearing bridgmanite to 120 GPa using optical pump-probe spectroscopy. The conductivity of Fe-bearing bridgmanite increases monotonically with pressure but drops significantly around 45 GPa due to pressure-induced lattice distortion on iron sites. Our findings indicate that lattice thermal conductivity at lowermost mantle conditions is twice smaller than previously thought. The decrease in the thermal conductivity of bridgmanite in mid-lower mantle and below would promote mantle flow against a potential viscosity barrier, facilitating slabs crossing over the 1000 km depth. Modeling of our results applied to LLSVPs shows that variations in iron and bridgmanite fractions induce a significant thermal conductivity decrease, which would enhance internal convective flow. Our CMB heat flux modeling indicates that while heat flux variations are dominated by thermal effects, variations in thermal conductivity also play a significant role. The CMB heat flux map we obtained is substantially different from those assumed so far, which may influence our understanding of the geodynamo.

58 GEOSCIENCES↗
DOE OSTI2018

Frequency shift of an optical frequency standard as a function of probe modulation of the radiation frequency, pressure, and gas temperature in an absorbing cell

Frequency shifts of an optical Nd : YAG/I{sub 2}-standard are measured in a pressure range of molecular iodine 5 – 22 mTorr and deviation of probe modulation frequency 480 kHz – 4 MHz for the hyperfine structure component a1 of the molecular iodine absorption line R(56) 32 – 0. The frequency shift of the optical standard is estimated under varied temperatures of a cell and cell finger, which determines the pressure of the molecular iodine vapour. The requirements are defined to temperature stability of the cell and its finger for obtaining high long-term frequency stability of the optical frequency standard. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1992

Method and apparatus for determining the physical properties of materials using dynamic light scattering techniques

A system for determining the physical properties of materials through the use of dynamic light scattering is disclosed. The system includes a probe, a laser source for directing a laser beam into the probe, and a photodetector for converting scattered light detected by the probe into electrical signals. The probe includes at least one optical fiber connected to the laser source and a second optical fiber connected to the photodetector. Each of the fibers may adjoin a gradient index microlens which is capable of providing a collimated laser beam into a scattering medium. The position of the second optical fiber with respect to the optical axis of the probe determines whether homodyne or self-beating detection is provided. Self-beating detection may be provided without a gradient index microlens. This allows a very small probe to be constructed which is insertable through a hypodermic needle or the like into a droplet extending from such a needle. A method of detecting scattered light through the use of a collimated, Gaussian laser beam is also provided. A method for controlling the waist and divergence of the optical field emanating from the free end of an optical fiber is also provided.

Dhadwal, Harbans S.↗
DOE OSTI2023

Adaptive Optical Two-Photon Fluorescence Microscopy Probes Cellular Organization of Ocular Lenses In Vivo

The mammalian ocular lens is an avascular multicellular organ that grows continuously throughout life. Traditionally, its cellular organization is investigated using dissected lenses, which eliminates in vivo environmental and structural support. Therefore, in vivo optical imaging methods for studying lenses in their native context in live animals are urgently needed. Here, we demonstrated that two-photon fluorescence microscopy can visualize lens cells in vivo. To maintain subcellular resolution at depth, we used adaptive optics to correct aberrations owing to ocular and lens tissues, which led to substantial signal and resolution improvements. Imaging lens cells up to 980 µm deep, we observed novel cellular organizations including suture-associated voids, enlarged vacuoles, and large cavities, contrary to the conventional view of a highly ordered organization. We tracked these features longitudinally over weeks and observed the incorporation of new cells during growth. Taken together, noninvasive longitudinal in vivo imaging of lens morphology using adaptive optics two-photon fluorescence microscopy will allow us to observe the development or alterations of lens cellular organization in living animals directly.

60 APPLIED LIFE SCIENCES↗