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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2008

Micron-Accurate Laser Fresnel-Diffraction Ranging System

Two versions of an optoelectronic system undergoing development are depicted. The system is expected to be capable of measuring a distance between 2 and 10 m with an error of no more than 1 micrometer. The system would be designed to exploit Fresnel diffraction of a laser beam. In particular, it would be designed to take advantage of the fact that a Fresnel diffraction pattern is ultrasensitive to distance. The two versions would differ in the following respects: In version 1, the focus of the telescope would be in the Fresnel region, and the telescope would have a small depth of focus. As a consequence, the Fresnel pattern would be imaged directly onto the photodetector array; in version 2, a multielement lens module would displace the Fresnel region from the vicinity of the pinhole to the vicinity of the optical receiver. As the distance to be measured varied, the location of the receiver relative to the displaced Fresnel-diffraction region would vary, thereby causing the Fresnel diffraction pattern on the focal plane to vary. The multielement lens module would also correct for aberrations. The processing of the digitized Fresnel diffraction pattern in the computer might be accelerated by using only parts of the pattern or even only one small part - the central pixel. As the distance from the pinhole increased, the central pixel would rapidly cycle between maximum and minimum light intensity. This in itself would not be sufficient to uniquely determine the distance. However, by varying the size of the pinhole or the wavelength of the laser, one could obtain a second cycle of variation of intensity that, in conjunction with the first cycle, could enable a unique determination of distance. Alternatively, for a single wavelength and a single pinhole size, it should suffice to consider the data from only two different key pixels in the Fresnel pattern.

Lehner, David↗
DOE OSTI2025

Fresnel diffraction imaging of surface nanostructure using coherent resonant x-ray scattering

We investigated surface nanostructures on an antiferromagnet MnBi 2 Te 4 using a novel imaging technique, direct (real)-space and real time coherent x-ray imaging (direct-CXI). This technique has provided new insights into antiferromagnetic textures, including the formation of anti-phase antiferromagnetic (AFM) domains and thermal dynamics of AFM domains and domain walls. While this method produces real-space images of AFM textures without requiring a complex imaging retrieval process, its underlying imaging mechanism has not been fully understood, limiting a deep understanding of AFM textures and the information they contain. By investigating the well-defined structural characteristics of the nanostructures fabricated on MnBi 2 Te 4 ⁠, we elucidate the imaging principle of this novel technique. We find that the observed images can be well explained by the Fresnel diffraction integral. Using a simple model from classical optics, our calculations successfully reproduce the experimentally observed images of the nanostructures. This demonstrates that direct-CXI not only provides straightforward real-space imaging but also contains phase information through its Fresnel diffraction integral.

36 MATERIALS SCIENCE↗
NASA NTRS1989

Fresnel diffraction by spherical obstacles

Lommel functions were used to solve the Fresnel-Kirchhoff diffraction integral for the case of a spherical obstacle. Comparisons were made between Fresnel diffraction theory and Mie scattering theory. Fresnel theory is then compared to experimental data. Experiment and theory typically deviated from one another by less than 10 percent. A unique experimental setup using mercury spheres suspended in a viscous fluid significantly reduced optical noise. The major source of error was due to the Gaussian-shaped laser beam.

Hovenac, Edward A.↗
DOE OSTI2023

Developing a platform for Fresnel diffractive radiography with 1 μ m spatial resolution at the National Ignition Facility

An x-ray Fresnel diffractive radiography platform was designed for use at the National Ignition Facility. It will enable measurements of micron-scale changes in the density gradients across an interface between isochorically heated warm dense matter materials, the evolution of which is driven primarily through thermal conductivity and mutual diffusion. Here we use 4.75 keV Ti K-shell x-ray emission to heat a 1000 μm diameter plastic cylinder, with a central 30 μm diameter channel filled with liquid D 2 , up to 8 eV. This leads to a cylindrical implosion of the liquid D 2 column, compressing it to ~2.3 g/cm 3 . After pressure equilibration, the location of the D 2 /plastic interface remains steady for several nanoseconds, which enables us to track density gradient changes across the material interface with high precision. For radiography, we use Cu He- α x rays at 8.3 keV. Using a slit aperture of only 1 μm width increases the spatial coherence of the source, giving rise to significant diffraction features in the radiography signal, in addition to the refraction enhancement, which further increases its sensitivity to density scale length changes at the D 2 /plastic interface.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1967

Fresnel diffraction plates are simple and inexpensive

Fresnel plate demonstrates diffraction phenomena simply and inexpensively. A large number of identical diffracting apertures are made in random orientation on photographic film. When a small source of light is viewed through the plate, the diffraction pattern typical of the diffracting aperture is readily seen.

Hoover, R. B.↗
NASA NTRS1999

Micron Accurate Absolute Ranging System: Range Extension

The purpose of this research is to investigate Fresnel diffraction as a means of obtaining absolute distance measurements with micron or greater accuracy. It is believed that such a system would prove useful to the Next Generation Space Telescope (NGST) as a non-intrusive, non-contact measuring system for use with secondary concentrator station-keeping systems. The present research attempts to validate past experiments and develop ways to apply the phenomena of Fresnel diffraction to micron accurate measurement. This report discusses past research on the phenomena, and the basis of the use Fresnel diffraction distance metrology. The apparatus used in the recent investigations, experimental procedures used, preliminary results are discussed in detail. Continued research and equipment requirements on the extension of the effective range of the Fresnel diffraction systems is also described.

Smalley, Larry L.↗
NASA NTRS2015

Linear Fresnel Spectrometer Chip with Gradient Line Grating

A spectrometer that includes a grating that disperses light via Fresnel diffraction according to wavelength onto a sensing area that coincides with an optical axis plane of the grating. The sensing area detects the dispersed light and measures the light intensity associated with each wavelength of the light. Because the spectrometer utilizes Fresnel diffraction, it can be miniaturized and packaged as an integrated circuit.

Choi, Sang Hyouk↗
NASA NTRS2010

SUB 1-Millimeter Size Fresnel Micro Spectrometer

An ultra-small micro spectrometer with less than 1mm diameter was constructed using Fresnel diffraction. The fabricated spectrometer has a diameter of 750 nmicrometers and a focal length of 2.4 mm at 533nm wavelength. The micro spectrometer was built with a simple negative zone plate that has an opaque center with an ecliptic shadow to remove the zero-order direct beam to the aperture slit. Unlike conventional approaches, the detailed optical calculation indicates that the ideal spectral resolution and resolving power do not depend on the miniaturized size but only on the total number of rings. We calculated 2D and 3D photon distribution around the aperture slit and confirmed that improved micro-spectrometers below 1mm size can be built with Fresnel diffraction. The comparison between mathematical simulation and measured data demonstrates the theoretical resolution, measured performance, misalignment effect, and improvement for the sub-1mm Fresnel micro-spectrometer. We suggest the utilization of an array of micro spectrometers for tunable multi-spectral imaging in the ultra violet range.

Park, Yeonjoon↗
DOE OSTI2022

Diffraction enhanced imaging utilizing a laser produced x-ray source

Image formation by Fresnel diffraction utilizes both absorption and phase-contrast to measure electron density profiles. The low spatial and spectral coherence requirements allow the technique to be performed with a laser-produced x-ray source coupled with a narrow slit. This makes it an excellent candidate for probing interfaces between materials at extreme conditions, which can only be generated at large-scale laser or pulsed power facilities. Here, we present the results from a proof-of-principle experiment demonstrating an effective ~2 μm laser-generated source at the OMEGA Laser Facility. This was achieved using slits of 1 × 30 μm 2 and 2 × 40 μm 2 geometry, which were milled into 30 μm thick Ta plates. Combining these slits with a vanadium He-like 5.2 keV source created a 1D imaging system capable of micrometer-scale resolution. The principal obstacles to achieving an effective 1 μm source are the slit tilt and taper—where the use of a tapered slit is necessary to increase the alignment tolerance. We demonstrate an effective source size by imaging a 2 ± 0.2 μm radius tungsten wire.

3D printing↗
DOE OSTI2024

Source size of x rays from self-modulated laser wakefield accelerators

A comparative study of x-ray sources generated with different mechanisms from self-modulated laser wakefield acceleration (SM-LWFA) electrons was performed to compare the source size or spatial resolution for use in high energy density science applications. We examine the source size of betatron, inverse Compton scattering, and bremsstrahlung radiation with a Fresnel diffraction based formalism and a modified x-ray ray tracing model. We observe the dependence of source size on the radiation generation process, laser parameters, and compare to what is possible in other regimes of LWFA, as well as current methods. This information is significant as we begin to explore the use of light sources driven by SM-LWFA for use as a diagnostic at large-scale laser facilities where blowout regime LWFA is not possible.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1987

Power and charge dissipation from an electrodynamic tether

The Plasma Motor-Generator project utilizes the influence of the geomagnetic field on a conductive tether attached to a LEO spacecraft to provide a reversible conversion of orbital energy into electrical energy. The behavior of the current into the ionospheric plasma under the influence of the geomagnetic field is of significant experimental and theoretical interest. Theoretical calculations are reviewed which start from Maxwell's equations and treat the ionospheric plasma as a linear dielectric medium. These calculations show a charge emitting tether moving in a magnetic field will generate electromagnetic waves in the plasma which carry the charge in the direction of the magnetic field. The ratio of the tether's speed to the ion cyclotron frequency which is about 25 m for a LEO is a characteristic length for the phenomena. Whereas for the dimensions of the contact plasma much larger than this value the waves are the conventional Alfven waves, when the dimensions are comparable or smaller, diffraction effects occur similar to those associated with Fresnel diffraction in optics. The power required to excite these waves for a given tether current is used to estimate the impedance associated with this mode of charge dissipation.

Hite, Gerald E.↗
NASA NTRS1999

Investigation of Next-Generation Earth Radiation Budget Radiometry

The current effort addresses two issues important to the research conducted by the Thermal Radiation Group at Virginia Tech. The first research topic involves the development of a method which can properly model the diffraction of radiation as it enters an instrument aperture. The second topic involves the study of a potential next-generation space-borne radiometric instrument concept. Presented are multiple modeling efforts to describe the diffraction of monochromatic radiant energy passing through an aperture for use in the Monte-Carlo ray-trace environment. Described in detail is a deterministic model based upon Heisenberg's uncertainty principle and the particle theory of light. This method is applicable to either Fraunhofer or Fresnel diffraction situations, but is incapable of predicting the secondary fringes in a diffraction pattern. Also presented is a second diffraction model, based on the Huygens-Fresnel principle with a correcting obliquity factor. This model is useful for predicting Fraunhofer diffraction, and can predict the secondary fringes because it keeps track of phase. NASA is planning for the next-generation of instruments to follow CERES (Clouds and the Earth's Radiant Energy System), an instrument which measures components of the Earth's radiant energy budget in three spectral bands. A potential next-generation concept involves modification of the current CERES instrument to measure in a larger number of wavelength bands. This increased spectral partitioning would be achieved by the addition of filters and detectors to the current CERES geometry. The capacity of the CERES telescope to serve for this purpose is addressed in this thesis.

Coffey, Katherine L.↗
DOE OSTI2022

Diffraction and thermal effect of a Bessel-Gaussian laser for Ag nanoparticle deposition

Nanoparticles are known to sinter at much lower temperatures than the corresponding bulk or micro size particles. A laser-assisted sintering process is considered in this study to sinter Ag nanoparticles by dispensing Ag paste onto an indium tin oxide-coated Si substrate. The Gaussian beam of a CO 2 laser source is propagated through axicon and biconvex lenses, and the resulting hollow beam is focused on the Ag paste with a hollow parabolic mirror. A Bessel-Gaussian irradiance distribution is obtained at the focal plane of the parabolic mirror due to the interference of the hollow laser cone. The Fresnel diffraction approximation is considered to determine the phasor of the laser and an analytical approach is implemented to calculate the irradiance distribution of the Bessel-Gaussian beam. This irradiance distribution is utilized as a heat source in a heat conduction model and the temperature distribution is analyzed for thin Ag films formed during the laser sintering of Ag nanoparticles. An analytical expression is obtained for the temperature distribution by solving the heat conduction equation using Fourier transform for finite media. The widths of the deposited Ag lines are predicted from the temperature profiles and the model predictions compare well with the experimental results. The isotherms are found to be geometrically noncongruent with convex and concave tips depending on the locally maximum and minimum irradiances of the Bessel-Gaussian beam, respectively. The convex and concave tips, however, appear in the same isotherm for sufficiently high substrate speed relative to the laser beam.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS2007

Can the Hypothesis 'Photon Interferes only with Itself' be Reconciled with Superposition of Light from Multiple Beams or Sources?

Any superposition effect as measured (SEM) by us is the summation of simultaneous stimulations experienced by a detector due to the presence of multiple copies of a detectee each carrying different values of the same parameter. We discus the cases with light beams carrying same frequency for both diffraction and multiple beam Fabry-Perot interferometer and also a case where the two superposed light beams carry different frequencies. Our key argument is that if light really consists of indivisible elementary particle, photon, then it cannot by itself create superposition effect since the state vector of an elementary particle cannot carry more than one values of any parameter at the same time. Fortunately, semiclassical model explains all light induced interactions using quantized atoms and classical EM wave packet. Classical physics, with its deeper commitment to Reality Ontology, was better prepared to nurture the emergence of Quantum Mechanics and still can provide guidance to explore nature deeper if we pay careful attention to successful classical formulations like Huygens-Fresnel diffraction integral.

Roychoudhuri, Chandrasekhar↗
DOE OSTI2022

Toward an integrated platform for characterizing laser-driven, isochorically heated plasmas with 1 µm spatial resolution

Warm dense matter is a region of phase space that is of high interest to multiple scientific communities ranging from astrophysics to inertial confinement fusion. Further understanding of the conditions and properties of this complex state of matter necessitates experimental benchmarking of the current theoretical models. We discuss the development of an x-ray radiography platform designed to measure warm dense matter transport properties at large laser facilities such as the OMEGA Laser Facility. Our platform, Fresnel Diffractive Radiography, allows for high spatial resolution imaging of isochorically heated targets, resulting in notable diffractive effects at sharp density gradients that are influenced by transport properties such as thermal conductivity. We discuss initial results, highlighting the capabilities of the platform in measuring diffractive features with micron-level spatial resolution.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1979

Stellar occultation studies of the solar system

The paper covers the principles, observational procedures, and results relating to occultations of stars by solar system bodies other than the moon. Physical processes involved in occultations are presented including (1) extinction by ring material, (2) differential refraction by a planetary atmosphere, (3) extinction by a planetary atmosphere, and (4) Fresnel diffraction by sharp edges. It is noted that from a sufficient number of immersion and emersion timings of a stellar occultation, the radius and ellipticity of the occulting body can be accurately determined. From an occultation by a planet having an atmosphere, temperature, pressure, and number density profiles can be obtained along with information about the composition of the atmosphere and the extinction.

Elliot, J. L.↗
NASA NTRS1988

Measurement and modeling of land mobile satellite propagation at UHF and L-band

A propagation experiment is described in which a stratospheric balloon served as a transmitter platform at 870 and 1502 MHz in simulation of a land mobile satellite. A vehicle followed the drifting balloon along roads of western Texas and New Mexico, collecting at L-band amplitude and phase, and at UHF amplitude information only for elevation angles between 25 and 45 deg. The data obtained have been analyzed and are presented along with results from modeling of multipath scattering and roadside tree attenuation. The signal, with variations caused by multipath propagation and tree shadowing, was reduced by 3 dB at L-band and 2 dB at UHF for one percent of all locations. A median ratio of 3.9 was found between peak-to-peak phase (degrees) and power (dB) fluctuations. The ratio between L-band and UHF dB attenuation averages varied from 1.3 to 1.0 at fade levels from 6 to 23 dB. Optical sky brightness was measured and used to predict fade distribution with great accuracy. A single-scatterer multipath model is introduced. It is used to duplicate some of the measured data and to show the dependence of power variations on satellite elevation angle. Using Fresnel diffraction theory, the attenuation caused by a model tree was calculated to be near 10 dB and the maximum fade was found to increase by the logarithm of the number of branches.

Vogel, Wolfhard J.↗