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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Flow-induced birefringence measurement system using dual-crystal transverse electro-optic modulator for microgravity fluid physics applications

We have developed a new instrument that can measure fast transient birefringence and polymer chain orientation angle in complex fluids. The instrument uses a dual-crystal transverse electro-optic modulator with the second crystal's modulation voltage applied 180 deg out of phase from that of the first crystal. In this manner, the second crystal compensates for the intrinsic static birefringence of the first crystal, and it doubles the modulation depth. By incorporating a transverse electro-optic modulator with two lithium-niobate (LiNbO3) crystals oriented orthogonal to each other with a custom-designed optical system, we have produced a very small robust instrument capable of fast transient retardation measurements. By measuring the sample thickness or optical path length through the sample, we can calculate the transient birefringence. This system can also measure dichroism. We have compared the calibration results and retardation and orientation angle measurements of this instrument with those of a photoelastic modulator (PEM) based system using a quarter wave plate and a high-precision 1/16-wave plate to simulate a birefringent sample. Transient birefringence measurements on the order of 10(exp -9) can be measured using either modulator.

Mackey, Jeffrey R.↗
DOE OSTI2022

A Pockels cell enabled heterodyne phase contrast imaging diagnostic for detection of ion cyclotron emission

This work describes a novel optical heterodyne detection scheme that significantly extends the frequency response of the phase contrast imaging method to detect electron density fluctuations in tens of megahertz frequency range. The system employs a variable frequency electro-optic modulator to allow operation at any frequency in the range 10–40 MHz without the need to realign the system. The frequency coverage of the system makes it suitable to measure the radial structure of the electron density component of ion cyclotron emission on devices having confining magnetic field of a few tesla, thus extending the purely temporal measurements provided so far by magnetic probes.

47 OTHER INSTRUMENTATION↗
NASA NTRSDate not supplied

Enhanced Far Ultra-Violet Optical Properties of Physical Vapor Deposited Aluminum Mirrors Through Fluorination

Astronomical instrumentation for measurements in the Far Ultra-Violet (FUV, 90-200 nm) typically use aluminum (Al) thin films due to their high reflectance over this wavelength range. However, the native aluminum oxide layer that forms on Al upon exposure to the atmosphere is strongly absorbing in this wavelength range, requiring that the films be protected with a dielectric that inhibits oxidation. Typically, magnesium fluoride (MgF 2 ) or lithium fluoride (LiF) coatings are used as protective layers, but each has shortcomings. For example, MgF 2 has an absorption cutoff at 115 nm reducing performance in a critical part of the FUV spectrum of observational interest. A viable option to access these lower wavelengths could be the use of the LiF overcoat as it has a lower absorption cutoff at 102.5 nm, but it is hygroscopic and thus susceptible to degradation in humid conditions. An approach to reduce the hygroscopic nature of LiF would be to implement a passivation process during the deposition of both Al+LiF coatings. Our team at GSFC has developed a new reactive Physical Vapor Deposition (rPVD) process that consists of a fluorination process with XeF 2 gas combined with our traditional PVD process. We have found that this new rPVD coating process offers a protected version of Al+LiF with a more environmentally stable and more transparent LiF layer, along with unprecedent reflectivity. The process starts with a bare optically smooth substrate that is coated with Al in an ultra-high vacuum (UHV) chamber by the conventional PVD process. Then, the bare Al mirror is immediately exposed to a reactive XeF 2 gas before and after the application of the flash PVD evaporated LiF layer. We have also been investigating the use of this rPVD coating process for potential efficiency enhancements of Si-based gratings. Since it is known that the XeF 2 vapor is a strong Si etchant, we are investigating if the native SiO 2 layer on Si is sufficient to protect the groove profile of e-beam-ruled Si gratings from degradation. We will report on the characterization of various Al+LiF witness mirror coatings (both on borosilicate and Si) performed under various deposition conditions using the XeF 2 passivation process. These tests include XPS to determine film stoichiometry and AFM/SEM to measure surface roughness and any etching on the Si substrate. We will also report on FUV reflectance and spectroscopic ellipsometry to characterize optical constants of these passivated films in the UV/Visible/NIR spectral ranges.

Engineering (General)↗
NASA NTRSDate not supplied

Enhanced Far Ultra-Violet Optical Properties of Physical Vapor Deposited Aluminum Mirrors Through Fluorination

Astronomical instrumentation for measurements in the Far Ultra-Violet (FUV, 90-200 nm) typically use aluminum (Al) thin films due to their high reflectance over this wavelength range. However, the native aluminum oxide layer that forms on Al upon exposure to the atmosphere is strongly absorbing in this wavelength range, requiring that the films be protected with a dielectric that inhibits oxidation. Typically, magnesium fluoride (MgF 2 ) or lithium fluoride (LiF) coatings are used as protective layers, but each has shortcomings. For example, MgF 2 has an absorption cutoff at 115 nm reducing performance in a critical part of the FUV spectrum of observational interest. A viable option to access these lower wavelengths could be the use of the LiF overcoat as it has a lower absorption cutoff at 102.5 nm, but it is hygroscopic and thus susceptible to degradation in humid conditions. An approach to reduce the hygroscopic nature of LiF would be to implement a passivation process during the deposition of both Al+LiF coatings. Our team at GSFC has developed a new reactive Physical Vapor Deposition (rPVD) process that consists of a fluorination process with XeF 2 gas combined with our traditional PVD process. We have found that this new rPVD coating process offers a protected version of Al+LiF with a more environmentally stable and more transparent LiF layer, along with unprecedent reflectivity. The process starts with a bare optically smooth substrate that is coated with Al in an ultra-high vacuum (UHV) chamber by the conventional PVD process. Then, the bare Al mirror is immediately exposed to a reactive XeF 2 gas before and after the application of the flash PVD evaporated LiF layer. We have also been investigating the use of this rPVD coating process for potential efficiency enhancements of Si-based gratings. Since it is known that the XeF 2 vapor is a strong Si etchant, we are investigating if the native SiO 2 layer on Si is sufficient to protect the groove profile of e-beam-ruled Si gratings from degradation. We will report on the characterization of various Al+LiF witness mirror coatings (both on borosilicate and Si) performed under various deposition conditions using the XeF 2 passivation process. These tests include XPS to determine film stoichiometry and AFM/SEM to measure surface roughness and any etching on the Si substrate. We will also report on FUV reflectance and spectroscopic ellipsometry to characterize optical constants of these passivated films in the UV/Visible/NIR spectral ranges.

Engineering (General)↗
NASA NTRSDate not supplied

Enhanced Far Ultra-Violet Optical Properties of Physical Vapor Deposited Aluminum Mirrors Through Fluorination

Astronomical instrumentation for measurements in the Far Ultra-Violet (FUV, 90-200 nm) typically use aluminum (Al) thin films due to their high reflectance over this wavelength range. However, the native aluminum oxide layer that forms on Al upon exposure to the atmosphere is strongly absorbing in this wavelength range, requiring that the films be protected with a dielectric that inhibits oxidation. Typically, magnesium fluoride (MgF 2 ) or lithium fluoride (LiF) coatings are used as protective layers, but each has shortcomings. For example, MgF 2 has an absorption cutoff at 115 nm reducing performance in a critical part of the FUV spectrum of observational interest. A viable option to access these lower wavelengths could be the use of the LiF overcoat as it has a lower absorption cutoff at 102.5 nm, but it is hygroscopic and thus susceptible to degradation in humid conditions. An approach to reduce the hygroscopic nature of LiF would be to implement a passivation process during the deposition of both Al+LiF coatings. Our team at GSFC has developed a new reactive Physical Vapor Deposition (rPVD) process that consists of a fluorination process with XeF 2 gas combined with our traditional PVD process. We have found that this new rPVD coating process offers a protected version of Al+LiF with a more environmentally stable and more transparent LiF layer, along with unprecedent reflectivity. The process starts with a bare optically smooth substrate that is coated with Al in an ultra-high vacuum (UHV) chamber by the conventional PVD process. Then, the bare Al mirror is immediately exposed to a reactive XeF 2 gas before and after the application of the flash PVD evaporated LiF layer. We have also been investigating the use of this rPVD coating process for potential efficiency enhancements of Si-based gratings. Since it is known that the XeF 2 vapor is a strong Si etchant, we are investigating if the native SiO 2 layer on Si is sufficient to protect the groove profile of e-beam-ruled Si gratings from degradation. We will report on the characterization of various Al+LiF witness mirror coatings (both on borosilicate and Si) performed under various deposition conditions using the XeF 2 passivation process. These tests include XPS to determine film stoichiometry and AFM/SEM to measure surface roughness and any etching on the Si substrate. We will also report on FUV reflectance and spectroscopic ellipsometry to characterize optical constants of these passivated films in the UV/Visible/NIR spectral ranges.

Engineering (General)↗
DOE OSTI2024

Real space iterative reconstruction for vector tomography (RESIRE-V)

Tomography has had an important impact on the physical, biological, and medical sciences. To date, most tomographic applications have been focused on 3D scalar reconstructions. However, in some crucial applications, vector tomography is required to reconstruct 3D vector fields such as the electric and magnetic fields. Over the years, several vector tomography methods have been developed. Here, we present the mathematical foundation and algorithmic implementation of REal Space Iterative REconstruction for Vector tomography, termed RESIRE-V. RESIRE-V uses multiple tilt series of projections and iterates between the projections and a 3D reconstruction. Each iteration consists of a forward step using the Radon transform and a backward step using its transpose, then updates the object via gradient descent. Incorporating with a 3D support constraint, the algorithm iteratively minimizes an error metric, defined as the difference between the measured and calculated projections. The algorithm can also be used to refine the tilt angles and further improve the 3D reconstruction. To validate RESIRE-V, we first apply it to a simulated data set of the 3D magnetization vector field, consisting of two orthogonal tilt series, each with a missing wedge. Our quantitative analysis shows that the three components of the reconstructed magnetization vector field agree well with the ground-truth counterparts. We then use RESIRE-V to reconstruct the 3D magnetization vector field of a ferromagnetic meta-lattice consisting of three tilt series. Our 3D vector reconstruction reveals the existence of topological magnetic defects with positive and negative charges. We expect that RESIRE-V can be incorporated into different imaging modalities as a general vector tomography method. To make the algorithm accessible to a broad user community, we have made our RESIRE-V MATLAB source codes and the data freely available at https://github.com/minhpham0309/RESIRE-V.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

Simulations of wavelength-multiplexed holography for single-shot spatiotemporal characterization of NIF’s advanced radiographic capability (ARC) laser

We simulate the use of a newly developed single-shot wavelength-multiplexed holography-based diagnostic, STRIPED FISH, to fully characterize the as-delivered laser pulses of the National Ignition Facility’s Advanced Radiographic Capability (NIF-ARC) laser. To that end, we have performed simulations of the NIF-ARC pulse incorporating (a) a time-integrated spatial-profile measurement and a complete temporal-intensity-and-phase measurement using a frequency resolved optical gating, but without any spatiotemporal pulse characterizations, and (b) simulated first-order spatiotemporal distortions, which could be measured on a single shot if a STRIPED FISH device were deployed.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

On the relative importance of the different initial conditions that seed the electrothermal instability

Electrothermal instability is responsible for degrading numerous applications of pulsed-power technology, yet the initial conditions from which it grows are not well understood. For the first time, metal surfaces have been tracked from characterization to self-emission. This reveals no clear correlation between non-uniform thermal emissions and surface metallurgical defects or crystallographic grains, while correlations are observed with surface topography for 5N metal but not 6061 metal. Finally, for 5N metal, surfaces with average roughness as small as 5nm still admit thermal perturbations with δT/T >0.1.

42 ENGINEERING↗
DOE OSTI2022

Chemical reactivity under collective vibrational strong coupling

Recent experiments of chemical reactions in optical cavities have shown great promise to alter and steer chemical reactions, but still remain poorly understood theoretically. In particular, the origin of resonant effects between the cavity and certain vibrational modes in the collective limit is still subject to active research. In this paper, we study the unimolecular dissociation reactions of many molecules, collectively interacting with an infrared cavity mode, through their vibrational dipole moment. We find that the reaction rate can slow down by increasing the number of aligned molecules, if the cavity mode is resonant with a vibrational mode of the molecules. We also discover a simple scaling relation that scales with the collective Rabi splitting, to estimate the onset of reaction rate modification by collective vibrational strong coupling and numerically demonstrate these effects for up to 10 4 molecules.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Laminography as a tool for imaging large-size samples with high resolution

Despite the increased brilliance of the new generation synchrotron sources, there is still a challenge with high-resolution scanning of very thick and absorbing samples, such as a whole mouse brain stained with heavy elements, and, extending further, brains of primates. Samples are typically cut into smaller parts, to ensure a sufficient X-ray transmission, and scanned separately. Compared with the standard tomography setup where the sample would be cut into many pillars, the laminographic geometry operates with slab-shaped sections significantly reducing the number of sample parts to be prepared, the cutting damage and data stitching problems. In this work, a laminography pipeline for imaging large samples (>1 cm) at micrometre resolution is presented. The implementation includes a low-cost instrument setup installed at the 2-BM micro-CT beamline of the Advanced Photon Source. Additionally, sample mounting, scanning techniques, data stitching procedures, a fast reconstruction algorithm with low computational complexity, and accelerated reconstruction on multi-GPU systems for processing large-scale datasets are presented. The applicability of the whole laminography pipeline was demonstrated by imaging four sequential slabs throughout an entire mouse brain sample stained with osmium, in total generating approximately 12 TB of raw data for reconstruction.

47 OTHER INSTRUMENTATION↗
NASA NTRS1984

The analysis of ocean optical data

A new oceanographic instrument to measure underwater optical, biological and physical properties simultaneously has been built and used extensively at sea. The Bio-Optical Profiling System (BOPS) was designed for the rapid acquisition of data to accommodate shipboard 'synoptic' sampling strategies, often in conjunction with concurrent aircraft and satellite sensors. The data rates and associated quantity of data from the BOPS are some orders of magnitude larger than those traditionally encountered in optical oceanography. The rapid acquisition of optical data in a wide range of environmental conditions requires new methodologies in ocean optical data analysis.

Smith, R. C.↗
NASA NTRS1981

Multichannel scanning radiometer for remote sensing cloud physical parameters

A multichannel scanning radiometer developed for remote observation of cloud physical properties is described. Consisting of six channels in the near infrared and one channel in the thermal infrared, the instrument can observe cloud physical parameters such as optical thickness, thermodynamic phase, cloud top altitude, and cloud top temperature. Measurement accuracy is quantified through flight tests on the NASA CV-990 and the NASA WB-57F, and is found to be limited by the harsh environment of the aircraft at flight altitude. The electronics, data system, and calibration of the instrument are also discussed.

Curran, R. J.↗