Engineering topics

Hoover, Richard B.

Publications and source records attributed to Hoover, Richard B..

At least 127 records · Page 7

NASA NTRS1993

Imaging Schwarzschild multilayer X-ray microscope

We have designed, analyzed, fabricated, and tested Schwarzschild multilayer X-ray microscopes. These instruments use flow-polished Zerodur mirror substrates which have been coated with multilayers optimized for maximum reflectivity at normal incidence at 135 A. They are being developed as prototypes for the Water Window Imaging X-Ray Microscope. Ultrasmooth mirror sets of hemlite grade sapphire have been fabricated and they are now being coated with multilayers to reflect soft X-rays at 38 A, within the biologically important 'water window'. In this paper, we discuss the fabrication of the microscope optics and structural components as well as the mounting of the optics and assembly of the microscopes. We also describe the optical alignment, interferometric and visible light testing of the microscopes, present interferometrically measured performance data, and provide the first results of optical imaging tests.

Hoover, Richard B.↗

NASA NTRS1993

Design and Fabrication of the All-Reflecting H-Lyman alpha Coronagraph/Polarimeter

We have designed, analyzed, and are now fabricating an All-Reflecting H-Lyman alpha Coronagraph/Polarimeter for solar research. This new instrument operates in a narrow bandpass centered at lambda 1215.7 A-the neutral hydrogen Lyman alpha (Ly-alpha) line. It is shorter and faster than the telescope which produced solar Ly-alpha images as a part of the MSSTA payload that was launched on May 13, 1991. The Ly-alpha line is produced and linearly polarized in the solar corona by resonance scattering, and the presence of a magnetic field modifies this polarization according to the Hanle effect. The Lyman alpha Coronagraph/Polarimeter instrument has been designed to measure coronal magnetic fields by interpreting, via the Hanle effect, the measured linear polarization of the coronal Ly-alpha line. Ultrasmooth mirrors, polarizers, and filters are being flow-polished for this instrument from CVD silicon carbide substrates. These optical components will be coated using advanced induced transmission and absorption thin film multilayer coatings, to optimize the reflectivity and polarization properties at 1215.7 A. We describe some of the solar imaging results obtained with the MSSTA Lyman alpha coronagraph. We also discuss the optical design parameters and fabrication plans for the All-Reflecting H-Lyman alpha Coronagraph/Polarimeter.

Hoover, Richard B.↗

NASA NTRS1992

X-ray monochromator

An x-ray monochromator is described, wherin a housing supports a plurality of mirrors forming a plurality of opposed mirror faces in parallel with each other and having thereon multilayer coatings, with each of said pairs of mirror faces being provided with identical coatings which are different from the coatings on the other pairs of mirror faces such that each pair of mirror faces has a peak x-ray reflection at a different wavelength regime. The housing is moveable to bring into a polychromatic x-ray beam that pair of mirror faces having the best x-ray reflection for the desired wavelength, with the mirrors being pivotable to move the mirror faces to that angle of incidence at which the peak reflectivity of the desired wavelength x-rays occurs.

Hoover, Richard B.↗

NASA NTRS1992

Multispectral variable magnification glancing incidence x ray telescope

A multispectral, variable magnification, glancing incidence, x-ray telescope capable of broadband, high resolution imaging of solar and stellar x-ray and extreme ultraviolet radiation sources is discussed. The telescope includes a primary optical system which focuses the incoming radiation to a primary focus. Two or more rotatable mirror carriers, each providing a different magnification, are positioned behind the primary focus at an inclination to the optical axis. Each carrier has a series of ellipsoidal mirrors, and each mirror has a concave surface covered with a multilayer (layered synthetic microstructure) coating to reflect a different desired wavelength. The mirrors of both carriers are segments of ellipsoids having a common first focus coincident with the primary focus. A detector such as an x-ray sensitive photographic film is positioned at the second respective focus of each mirror so that each mirror may reflect the image at the first focus to the detector at the second focus. The carriers are selectively rotated to position a selected mirror for receiving radiation from the primary optical system, and at least the first carrier may be withdrawn from the path of the radiation to permit a selected mirror on the second carrier to receive the radiation.

Hoover, Richard B.↗

NASA NTRS1992

Multilayer Monochromator For Hard X Rays And Gamma Rays

Compact monochromator for hard x rays and gamma rays provides high spectral resolution with high throughput. Resembles instruments in "Compact X-Ray and Extreme-Ultraviolet Monochromator" (MFS-28499), "Scanning X-Ray or Extreme-Ultraviolet Monochromator" (MFS-28492), "Ultra-High-Spectral-Resolution X-Ray/EUV Monochromator" (MFS-28500), and "Four-Mirror X-Ray and Extreme-Ultraviolet Monochromator" (MFS-28498). Operates on principle of multilayer Bragg reflector. Used in nuclear, astronomical, and biomedical research, x-ray crystallography, research on processing materials, research in x-ray lasers, and x-ray lithography.

Hoover, Richard B.↗

NASA NTRS1992

Water window imaging x ray microscope

A high resolution x ray microscope for imaging microscopic structures within biological specimens has an optical system including a highly polished primary and secondary mirror coated with identical multilayer coatings, the mirrors acting at normal incidence. The coatings have a high reflectivity in the narrow wave bandpass between 23.3 and 43.7 angstroms and have low reflectivity outside of this range. The primary mirror has a spherical concave surface and the secondary mirror has a spherical convex surface. The radii of the mirrors are concentric about a common center of curvature on the optical axis of the microscope extending from the object focal plane to the image focal plane. The primary mirror has an annular configuration with a central aperture and the secondary mirror is positioned between the primary mirror and the center of curvature for reflecting radiation through the aperture to a detector. An x ray filter is mounted at the stage end of the microscope, and film sensitive to x rays in the desired band width is mounted in a camera at the image plane of the optical system. The microscope is mounted within a vacuum chamber for minimizing the absorption of x rays in air from a source through the microscope.

Hoover, Richard B.↗

NASA NTRS1992

Multilayer and grazing incidence X-ray/EUV optics; Proceedings of the Meeting, San Diego, CA, July 22-24, 1991

The present conference discusses the Advanced X-ray Astrophysics Facility (AXAF) calibration by means of synchrotron radiation and its X-ray reflectivity, X-ray scattering measurements from thin-foil X-ray mirrors, lobster-eye X-ray optics using microchannel plates, space-based interferometry at EUV and soft X-ray wavelengths, a water-window imaging X-ray telescope, a graded d-spacing multilayer telescope for high energy X-ray astronomy, photographic films for the multispectral solar telescope array, a soft X-ray ion chamber, and the development of hard X-ray optics. Also discussed are X-ray spectroscopy with multilayered optics, a slit aperture for monitoring X-ray experiments, an objective double-crystal spectrometer, a Ly-alpha coronagraph/polarimeter, tungsten/boron nitride multilayers for XUV optical applications, the evaluation of reflectors for soft X-ray optics, the manufacture of elastically bent crystals and multilayer mirrors, and selective photodevices for the VUV.

Hoover, Richard B.↗

NASA NTRS1992

Design and analysis of soft X-ray imaging microscopes

The spherical Schwarzschild microscope for soft X-ray applications in microscopy and projection lithography consists of two concentric spherical mirrors configured such that the third-order spherical aberration and coma are zero. Since multilayers are used on the mirror substrates for X-ray applications, it is desirable to have only two reflecting surfaces in a microscope. To reduce microscope aberrations and increase the field of view, generalized mirror surface profiles are here considered. Based on incoherent and sine wave modulation transfer function calculations, the object plane resolution of a microscope has been analyzed as a function of the object height and numerical aperture (NA) of the primary for several spherical Schwarzschild, conic, and aspherical Head reflecting two-mirror microscope configurations. The Head microscope with a NA of 0.4 achieves diffraction limited performance for objects with a diameter of 40 microns. Thus, it seems possible to record images with a feature size less than 100 A with a 40x microscope when using 40 A radiation.

Shealy, David L.↗

NASA NTRS1992

Metrology of X-ray optics utilizing shearing interferometric techniques

This paper will discuss the optical testing of extreme grazing incidence mirror systems and normal incidence high-precision mirror systems during fabrication processing of the optical substrates. The optical metrology is closely coupled with an advanced material removal process which will be discussed in terms of the optical metrology. Interferometric data will be presented of the optical surfaces. Surface roughness data will be shown and discussed.

Baker, Phillip C.↗

NASA NTRS1992

Solar observations with the Multi-Spectral Solar Telescope Array

The Multi-Spectral Solar Telescope Array (MSSTA) is a sounding rocket-borne solar observatory which was succesfully launched on May 13, 1991, from the White Sands Missile Range, NM. Ultrahigh resolution, full-disk solar X-ray, EUV, and FUV images were obtained with the MSSTA Herschelian, Cassegrain, and Ritchey-Chretien telescopes. We describe the payload and provide some preliminary scientific results from the flight.

Hoover, Richard B.↗

NASA NTRS1992

Photographic films for the Multi-Spectral Solar Telescope Array

The rocketborne Multi-Spectral Solar Telescope Array (MSSTA) uses an array of Ritchey-Chretien, Cassegrain, and Herschelian telescopes to produce ultrahigh-resolution full-disk images of the sun within the soft X-ray, EUV, and FUV ranges. Such imaging of the solar disk and corona out to several solar radii placed great demands on the MSSTA's data storage capabilities; in addition, its photographic films required very low outgassing rates. Results are presented from calibration tests conducted on the MSSTA's emulsions, based on measurements at NIST's synchrotron facility.

Hoover, Richard B.↗

NASA NTRS1992

The Ultra High Resolution XUV Spectroheliograph. III - A modified configuration for a free flying platform

The Ultra-High Resolution XUV Spectroheliograph (UHRXS) is a comprehensive solar observatory capable of studying solar phenomena at soft X-ray, XUV, EUV, and VUV wavelengths with normal incidence imaging multilayer telescopes capable of very high angular resolution (about 0.1 arcsec), and spectrographs able to achieve high spectral resolution. This instrument has been selected by NASA for flight as an attached payload on the Space Station Freedom. Recent developments have made it clear that accommodations for attached payloads on Freedom will not become available during the initial operations of Freedom and may never be available. We have studied the changes that must be made to place the UHRXS instrument on a Free Flying Plafform such as the Delta Launched Explorer Bus. We report on the configuration, performance, and accommodation on a free flying platform of the revised UHRXS concept.

Walker, Arthur B. C., Jr.↗

NASA NTRS1992

The Solar/Stellar Coronal Explorer and the Solar/Stellar Coronal Observatory

The Solar/Stellar Coronal Explorer (SSCE) carries six identical Ritchey-Chretien Telescopes of 127 mm aperture each; their images will be recorded by multianode microchannel-array detectors. The mirrors of five of the telescopes are coated with multilayer reflecting structures that select narrow XUV wavelength bands corresponding to strong emission lines emitted by solar or stellar coronal plasmas. Also noted here is a larger explorer mission concept, that of the Solar/Stellar Coronal Observatory, which will undertake more extensive spectroscopic observations.

Walker, Arthur B. C., Jr.↗

NASA NTRS1992

Cosmic X-ray spectroscopy with multilayer optics

Multilayer optics operated at normal incidence offer a powerful new technology for the study of the solar spectrum in the XUV. The spectra of most cosmic X-ray sources are strongly extinguished at wavelengths above 40 A due to absorption and scattering by interstellar grains. We describe a number of configurations which allow multilayer optics to be used at nonnormal angles of incidence in conjunction with grazing incidence optics to analyze the spectra of cosmic X-ray sources in the wavelength interval between 1.5 and 40 A. These optical configurations utilize both multilayer mirrors and gratings, and permit the efficient observation of extended sources using stigmatic spectrographs. The response of the instruments described to typical cosmic X-ray sources is also discussed.

Walker, Arthur B. C., Jr.↗

NASA NTRS1992

Narrow band solar images in the soft X-ray regime with multilayer optics

High quality multilayers with 2d spacings as short as about 44 A have been used successfully for astronomical observations. Observation of both the sun and cosmic X-ray sources (for which radiation longward of the carbon edge at about 44 A is strongly attenuated by interstellar matter) are possible at wavelengths shorter than 40 A with current multilayer technology, if mirrors are used at nonnormal angles of incidence. We discuss several configurations which are suitable for high resolution solar imaging observations in the wavelength interval between 0.5 and 50 A. We also describe the design and anticipated performance of a multilayer optical system we are currently developing for a rocketborne solar observatory.

Walker, Arthur B. C., Jr.↗

NASA NTRS1992

The High Resolution Telescope Cluster. I - Overview and technical status

A major component of the Advanced Solar Observatory is the High Resolution Telescope Cluster (HRTC) for investigations of the solar atmosphere at soft X-ray, XUV, EUV, and VUV wavelengths, via high resolution spectroheliograms in lines and continuum emitted over the full, (4500 to 100,000,000 K) range of temperatures of the outer solar atmosphere; angular resolution may be as high as 0.03 arcsec. An analysis is conducted of a model HRTC instrument complement encompassing a 60-90 cm aperture VUV telescope, a 40-50 cm aperture EUV telescope, three 40-50 cm aperture XUV telescopes, and a 40-cm aperture soft X-ray telescope, as well as flare spectrometers and polarimeters and four coronagraph/spectrographs.

Walker, Arthur B. C., Jr.↗

NASA NTRS1992

Hydrogen Lyman-alpha coronagraph/polarimeter

The present treatment of vector magnetic field measurement in coronas by means of the Hanle effect of the Lyman-alpha line uses data from all-reflecting imaging coronagraph/polarimeters. The polarization sensitivity, bandpass, and spatial resolution of these instruments are defined through a modeling of the Hanle-effect signature in Lyman-alpha emission from coronal magnetic loops; the line-of-sight integration through an inhomogeneous coronal medium is taken into account. The use of the Hanle effect to measure solar corona vector magnetic fields is verified.

Fineschi, Silvano↗

NASA NTRS1992

Optical configurations of H I Lyman-alpha coronagraph/polarimeters

The Multi-Spectral Solar Telescope Array (MSSTA) has obtained numerous high-resolution soft X-ray/EUV/FUV solar images with multilayer telescopes; these show dramatic prominences, spicules, and threadlike limb structures. There is excellent correlation between faint Lyman-alpha coronal structures seen in the digitized MSSTA images and prominences seen in H-alpha images gathered by ground-based observatories. The MSSTA has established the feasibility of an all-reflecting, imaging Ly-alpha coronagraph/polarimeter.

Hoover, Richard B.↗