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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 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Lens Design Using Group Indices of Refraction

An approach to lens design is described in which the ratio of the group velocity to the speed of light (the group index) in glass is used, in conjunction with the more familiar phase index of refraction, to control certain chromatic properties of a system of thin lenses in contact. The first-order design of thin-lens systems is illustrated by examples incorporating the methods described.

optical glass interferometry ultrashort pulses↗
NASA NTRS2000

Asronomical refraction: Computational methods for all zenith angles

It is shown that the problem of computing astronomical refraction for any value of the zenith angle may be reduced to a simple, nonsingular, numerical quadrature when the proper choice is made for the independent variable of integration.

Computing numerical methods refractions↗
DOE OSTI2020

Refractive Imaging of Air Shock Above Microscale Defects in Pentaerythritol Tetranitrate (PETN) Films

Physical vapor deposition (PVD) of high explosives can produce energetic samples with unique microstructure and morphology compared to traditional powder processing techniques, but challenges may exist in fabricating explosive films without defects. Deposition conditions and substrate material may promote microcracking and other defects in the explosive films. Here, we investigate effects of engineered microscale defects (gaps) on detonation propagation and failure for pentaerythritol tetranitrate (PETN) films using ultra-high-speed refractive imaging and hydrocode modelling. Observations of the air shock above the gap reveal significant instabilities during gap crossing and re-ignition.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Porous Silicon Gradient Refractive Index Micro-Optics

We see the emergence and growth of transformation optics over the past decade has revitalized interest in how a gradient refractive index (GRIN) can be used to control light propagation. Two-dimensional demonstrations with lithographically defined silicon (Si) have displayed the power of GRIN optics and also represent a promising opportunity for integrating compact optical elements within Si photonic integrated circuits. Here, we demonstrate the fabrication of three-dimensional Si-based GRIN micro-optics through the shape-defined formation of porous Si (PSi). Conventional microfabrication creates Si square microcolumns (SMCs) that can be electrochemically etched into PSi elements with nanoscale porosity along the shape-defined etching pathway, which imparts the geometry with structural birefringence. Free-space characterization of the transmitted intensity distribution through a homogeneously etched PSi SMC exhibits polarization splitting behavior resembling that of dielectric metasurfaces that require considerably more laborious fabrication. Coupled birefringence/GRIN effects are studied by way of PSi SMCs etched with a linear (increasing from edge to center) GRIN profile. The transmitted intensity distribution shows polarization-selective focusing behavior with one polarization focused to a diffraction-limited spot and the orthogonal polarization focused into two laterally displaced foci. Optical thickness-based analysis readily predicts the experimentally observed phenomena, which strongly match finite-element electromagnetic simulations.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Interferometric measurements of refractive index and dispersion at high pressure

Abstract We describe a high precision interferometer system to measure the pressure dependence of the refractive index and its dispersion in the diamond anvil cell (DAC). The reflective Fabry–Perot fringe patterns created by both a white light and a monochromatic beam are recorded to determine both the sample thickness and its index at the laser wavelength and to characterize the dispersion in the visible range. Advances in sample preparation, optical setup, and data analysis enable us to achieve $$10^{-4}$$ 10 - 4 random uncertainty, demonstrated with an air sample, a factor of five improvement over the best previous DAC measurement. New data on $${\text{H}}_{2}\text{O}$$ H 2 O liquid water and ice VI up to 2.21 GPa at room temperature illustrate how higher precision measurements of the index and its optical dispersion open up new opportunities to reveal subtle changes in the electronic structure of water at high pressure.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Thermal transport in warm dense matter revealed by refraction-enhanced x-ray radiography with a deep-neural-network analysis

Abstract Transport properties of high energy density matter affect the evolution of many systems, ranging from the geodynamo in the Earth’s core, to hydrodynamic instability growth in inertial confinement fusion capsules. Large uncertainties of these properties are present in the warm dense matter regime where both plasma models and condensed matter models become invalid. To overcome this limit, we devise an experimental platform based on x-ray differential heating and time-resolved refraction-enhanced radiography coupled to a deep neural network. We retrieve the first measurement of thermal conductivity of CH and Be in the warm dense matter regime and compare our measurement with the most commonly adopted models. The discrepancies observed are related to the estimation of a correction term from electron-electron collisions. The results necessitate improvement of transport models in the warm dense matter regime and could impact the understanding of the implosion performance for inertial confinement fusion.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Monolithic graded-refractive-index glass-based antireflective coatings. Broadband/omnidirectional light harvesting and self-cleaning characteristics

The design of multifunctional coatings impact impact the performance of many optical systems and components. Such coatings should be mechanically robust, and combine user-defined optical and wetting functions with scalable fabrication formulations. By taking cues from the properties of some natural biological structures, we report here the formation of low-refractive index antireflective glass films that embody omni-directional optical properties over a wide range of wavelengths, while also possessing specific wetting capabilities. The coatings comprise an interconnected network of nanoscale pores surrounded by a nanostructured silica framework. These structures result from a novel fabrication method that utilizes metastable spinodal phase separation in glass-based materials. The approach not only enables design of surface microstructures with graded-index antireflection characteristics, where the surface reflection is suppressed through optical impedance matching between interfaces, but also facilitates self-cleaning ability through modification of the surface chemistry. Based on near complete elimination of Fresnel reflections (yielding >95% transmission through a single-side coated glass) and corresponding increase in broadband transmission, the fabricated nanostructured surfaces are found to promote a general and an invaluable ~3–7% relative increase in current output of multiple direct/indirect bandgap photovoltaic cells. Moreover, these antireflective surfaces also demonstrate superior resistance against mechanical wear and abrasion. Unlike conventional counterparts, the present antireflective coatings are essentially monolithic, enabling simultaneous realization of graded index anti-reflectivity, self-cleaning capability, and mechanical stability within the same surface. Moreover, the concept represents a fundamental basis for development of advanced coated optical quality products, especially where environmental exposure is required.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Imidazole-graphyne: a new 2D carbon nitride with a direct bandgap and strong IR refraction

Six-membered rings are common building blocks of many carbon structures. Recent studies have shown that penta-graphene composed of five-membered carbon rings have properties very different from that of graphene. This has motivated the search for new carbon structures. Among this is cp-graphyne, composed of carbon pentagons and bridged by acetylenic linkers. However, the bandgap of cp-graphyne, like that of graphene, is zero, making it unsuitable for applications in electronics. Herein, we show that a new two-dimensional (2D) carbon nitride structure formed by assembling the five-membered imidazole molecules with acetylenic linker can overcome this limitation. Named ID-GY, this new material not only has a direct band gap of 1.10 eV, but it is dynamically and mechanically stable and can withstand temperatures up to 1200 K. In addition, due to its porous and anisotropic geometry, the Young's modulus of ID-GY along the diagonal direction is lower than that of most 2D materials reported previously. Equally important, ID-GY exhibits strong refraction near infrared (IR) and has potential for applications in nanoelectronics and optical devices. These results, based on density functional theory, can stimulate experimental studies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Protecting against damage from refraction of high power microwaves in the DIII-D tokamak

Here, several new protective systems are being installed on the DIII D tokamak to increase the safety margins for plasma operations with injected ECH power at densities approaching cutoff. Inadvertent overdense operation has previously resulted in reflection of an rf beam back into a launcher causing extensive arcing and melt damage on one waveguide line. Damage to microwave diagnostics, which are located on the same side of the tokamak as the ECH launchers, also has occurred. Developing a reliable microwave based interlock to protect the many vulnerable systems in DIII-D has proved to be difficult. Therefore, multiple protective steps have been taken to reduce the risk of damage in the future. Among these is a density interlock generated by the plasma control system, with setpoint determined by the ECH operators based on rf beam trajectories and plasma parameters. Also installed are enhanced video monitoring of the launchers, and an ambient light monitor on each of the waveguide systems, along with a Langmuir probe at the mouth of each launcher. Versatile rf monitors, measuring forward and reflected power in addition to the mode content of the rf beams, have been installed as the last miter bends in each waveguide line. As these systems are characterized, they are being incorporated in the interlock chains, which enable the ECH injection permits. The diagnostics most susceptible to damage from the ECH waves have also been fitted with a variety of protective devices including stripline filters, thin resonant notch filters tuned to the 110 GHz injected microwave frequency, blazed grating filters and shutters. Calculations of rf beam trajectories in the plasmas are performed using the TORAY ray tracing code with input from kinetic profile diagnostics. Using these calculations, strike points for refracted beams on the vacuum vessel are calculated, which allows evaluation of the risk of damage to sensitive diagnostics and hardware.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Microfocused X-rays Beams Using Compound Refractive Lenses: Possibilities for Indus-2

For the generation of micro focused hard x-ray beams on Indus-2, with large depth of focus and large focal lengths, simulation studies have been performed using parabolic Be compound refractive lenses (CRLs). The use of these lenses is expected to open many new experimental possibilities widely used at other synchrotron sources.

43 PARTICLE ACCELERATORS↗
DOE OSTI2012

Refractive optical elements and optical system for high energy x-ray microscopy

In material science, X-ray radiation with photon energies above 25 keV is used because of its penetration into high density materials. Research of the inner structure of novel materials, such as electrodes in high power batteries for engines, require X-ray microscopes operating in the hard X-ray energy range. A flexible X-ray microscope for hard X-rays with photon energies higher than 25 keV will be realized at the synchrotron source ANKA in Karlsruhe, Germany. The device will use refractive X-ray lenses as condenser as well as objective lenses.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

Fabrication of compound refractive lens using soft and deep X-ray lithography beamline on Indus-2

X-ray compound refractive lenses (CRL) have been fabricated using Soft and Deep X-ray lithography (SDXRL) beamline on Indus-2. Upto 50 parabolic lenses are fabricated in PMMA using 1X X-ray mask. The mask contains of 20 micron thick gold absorbing pattern on polyimide membrane. The lens fabrication is done by exposing 500 {mu}m thick PMMA sheets to 5-12keV X-rays from Indus-2. The fabricated CRL will be suitable for generating focused X-ray beam of Indus-2 bending magnet source.

43 PARTICLE ACCELERATORS↗
DOE OSTI2012

Characterization of a one dimensional focusing compound refractive lens using the rotating shearing interferometer technique

A one dimensional (1D) compound refractive lens (CRL) has been characterized using the grating based rotating shearing interferometer technique. The method is based on the calculation of moire fringes orientation to sense wavefront information. The phase shift and the optical aberration introduced by the 1D CRL on an X-ray beam were retrieved from a single moire fringe image. The radius of curvature of the lens at the apex was derived. This physical radius of the CRL, which is also closely related to the focal length of the 1D CRL, was shown to vary with the incident angle of the incoming X-ray beam onto the CRL. The experimental measurement agreed very well with the theoretical expectations.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗