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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Optimized mirror shape tuning using beam weightings based on distance, angle of incidence, reflectivity, and power

For glancing-incidence optical systems, such as short-wavelength optics used for nano-focusing, incorporating physical factors in the calculations used for shape optimization can improve performance. Wavefront metrology, including the measurement of a mirror's shape or slope, is routinely used as input for mirror figure optimization on mirrors that can be bent, actuated, positioned, or aligned. Modeling shows that when the incident power distribution, distance from focus, angle of incidence, and the spatially varying reflectivity are included in the optimization, higher Strehl ratios can be achieved. Following the works of Maréchal and Mahajan, optimization of the Strehl ratio (for peak intensity with a coherently illuminated system) occurs when the expectation value of the phase error's variance is minimized. We describe an optimization procedure based on regression analysis that incorporates these physical parameters. This approach is suitable for coherently illuminated systems of nearly diffraction-limited quality. Mathematically, this work is an enhancement of the methods commonly applied for ex situ alignment based on uniform weighting of all points on the surface (or a sub-region of the surface). It follows a similar approach to the optimization of apodized and non-uniformly illuminated optical systems. Significantly, it reaches a different conclusion than a more recent approach based on minimization of focal plane ray errors.

47 OTHER INSTRUMENTATION↗
DOE OSTI2016

Measurement and models of bent KAP(001) crystal integrated reflectivity and resolution (invited)

The Advanced Light Source beamline-9.3.1 x-rays are used to calibrate the rocking curve of bent potassium acid phthalate (KAP) crystals in the 2.3-4.5 keV photon-energy range. Crystals are bent on a cylindrically convex substrate with a radius of curvature ranging from 2 to 9 in. and also including the flat case to observe the effect of bending on the KAP spectrometric properties. As the bending radius increases, the crystal reflectivity converges to the mosaic crystal response. The X-ray Oriented Programs (XOP) multi-lamellar model of bent crystals is used to model the rocking curve of these crystals and the calibration data confirm that a single model is adequate to reproduce simultaneously all measured integrated reflectivities and rocking-curve FWHM for multiple radii of curvature in both 1st and 2nd order of diffraction.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Porous Nanomaterials for Ultrabroadband Omnidirectional Anti‐Reflection Surfaces with Applications in High Concentration Photovoltaics

Materials for nanoporous coatings that exploit optimized chemistries and self‐assembly processes offer capabilities to reach ≈98% transmission efficiency and negligible scattering losses over the broad wavelength range of the solar spectrum from 350 nm to 1.5 µm, on both flat and curved glass substrates. These nanomaterial anti‐reflection coatings also offer wide acceptance angles, up to ±40°, for both s‐ and p‐polarization states of incident light. Carefully controlled bilayer films have allowed for the fabrication of dual‐sided, gradient index profiles on plano‐convex lens elements. In concentration photovoltaics platforms, the resultant enhancements in the photovoltaics efficiencies are ≈8%, as defined by experimental measurements on systems that use microscale triple‐junction solar cells. These materials and their applications in technologies that require control over interface reflections have the potential for broad utility in imaging systems, photolithography, light‐emitting diodes, and display technologies.

Yao, Yuan↗
DOE OSTI2012

Reflection-asymmetric nuclear deformations within the Density Functional Theory

Within the nuclear density functional theory (DFT) we study the effect of reflection-asymmetric shapes on ground-state binding energies and binding energy differences. To this end, we developed the new DFT solver AXIALHFB that uses an approximate second-order gradient to solve the Hartree-Fock-Bogoliubov equations of superconducting DFT with the quasi-local Skyrme energy density functionals. Illustrative calculations are carried out for even-even isotopes of radium and thorium.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Direct measurement of the static and transient magneto-optical permittivity of cobalt across the entire M -edge in reflection geometry by use of polarization scanning

The microscopic state of a magnetic material is characterized by its resonant magneto-optical response through the off-diagonal dielectric tensor component ε xy . However, the measurement of the full complex ε xy in the extreme ultraviolet spectral region covering the M absorption edges of 3d ferromagnets is challenging due to the need for either a careful polarization analysis, which is complicated by a lack of efficient polarization analyzers, or scanning the angle of incidence in fine steps. Here, we propose and demonstrate a technique to extract the complex resonant permittivity ε xy simply by scanning the polarization angle of linearly polarized high harmonics to measure the magneto-optical asymmetry in reflection geometry. Because this technique is more practical and faster to experimentally implement than previous approaches, we can directly measure the full time evolution of ε xy (t) during laser-induced demagnetization across the entire M 2,3 absorption edge of cobalt with femtosecond time resolution. We find that for polycrystalline Co films on an insulating substrate, the changes in ε xy are uniform throughout the spectrum, to within our experimental precision. This result suggests that, in the regime of strong demagnetization, the ultrafast demagnetization response is primarily dominated by magnon generation. Here, we estimate the contribution of exchange-splitting reduction to the ultrafast demagnetization process to be no more than 25%.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Design and laser damage properties of a dichroic beam combiner coating for 22.5-deg incidence and S polarization with high transmission at 527 nm and high reflection at 1054 nm

We designed a dichroic beam combiner coating with 11 HfO 2 /SiO 2 layer pairs and deposited it on a large substrate. It provides high transmission (HT) at 527 nm and high reflection (HR) at 1054 nm for a 22.5-deg angle of incidence (AOI), S polarization (Spol), and uses near half-wave layer thicknesses for HT at 527 nm, modified for HR at 1054 nm. The two options for the beam combiner each require that a high intensity beam be incident on the coating from within the substrate (from glass). We analyze the laser-induced damage threshold (LIDT) differences between the two options in terms of the 527- and 1054-nm E-field behaviors for air → coating and glass → coating incidences. This indicates that LIDTs should be higher for air → coating than for glass → coating incidence. LIDT tests at the use AOI, Spol with ns pulses at 532 and 1064 nm confirm this, with glass → coating LIDTs about half that of air → coating LIDTs. Lastly, these results clearly indicate that the best beam combiner option is for the high intensity 527 and 1054 nm beams to be incident on the coating from air and glass, respectively.

36 MATERIALS SCIENCE↗