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NASA NTRS1989

PC based graphic display real-time particle beam uniformity

A technique has been developed to support the study of the effects of cosmic rays on integrated circuits. The system is designed to determine the particle distribution across the surface of an integrated circuit accurately while the circuit is bombarded by a particle beam. The system uses photomultiplier tubes, an octal discriminator, a computer-controlled NIM quad counter, and an IBM PC. It provides real-time operator feedback for fast beam tuning and monitors momentary fluctuations in the particle beam. The hardware, software, and system performance are described.

Huebner, M. A.↗

NASA NTRS1990

A photoelectric astrometric telescope using a Ronchi ruling

A new generation of photoelectric astrometric telescopes promises significant advances for both semiglobal and differential astrometry. Some of these new telescopes have a Ronchi ruling at the prime focal plane. The images move relative to the ruling, behind which photomultipliers or similar detectors view the modulated transmitted light. When several stars are viewed simultaneously, this technique exploits correlations in the atmospheric seeing to significantly improve differential astrometric precision. This article presents some general design and analysis criteria for this type of telescope and describes the particular reflector telescope. This has a 29-cm aperture and has met a 4-milli-arc-second differential precision per 5-minute observation. The system is designed for a program of improved annual parallax and solar-system object measurements.

Buffington, Andrew↗

NASA NTRS1989

Hubble Space Telescope fine guidance sensor control system

The fine pointing information required for the extraordinary pointing stability of the Hubble Space Telescope (HST) is provided by the fine guidance sensor (FGS), which is capable of measuring extremely small pointing errors, of the order of 3 milliarcseconds. The FGS provides this fine pointing information over a relatively large, continuous range of angles of guide stars relative to the optical axis of the telescope. The FGS accomplishes this task by a judicious design involving the following: a two-axis high precision star selector servo system; an optical deflection system that provides high reduction from shaft angle to optical angle; a unique interferometer using Koester prisms and extremely sensitive photomultiplier tubes that enable the FGS to lock onto guide stars whose magnitude may be any value over a wide range of brightness (including 14.5 Mv and fainter); and the use the large aperture of the telescope itself to advantage. This paper describes the FGS control systems involved in achieving this performance, supported by test data.

Nurre, Gerald S.↗

NASA NTRS1990

A study of the scintillation light induced in liquid xenon by electrons and alpha particles

The time dependence and the intensity of the primary scintillation light in liquid Xe excited by Am-241 alpha particles and Bi-207 internal-conversion electrons were measured at different electric-field strengths. High-purity liquid Xe was used to fill a parallel-plate ionization chamber equipped with a CaF2 window coupled to a UV-sensitive photomultiplier tube. The effect of the specific ionization density on the scintillation light and the time correlation between the light signal and the charge signal is reported. It is demonstrated that the fast scintillation signal produced in liquid Xe by an ionizing particle provides an ideal trigger in a detector aiming at a complete three-dimensional event reconstruction with an excellent background rejection capability.

Aprile, Elena↗

NASA NTRS1989

Solar flare X-ray polarimeter utilizing a large area thin beryllium scattering disk

A model of a solar flare X-ray polarimeter utilizing a large-area thin beryllium scattering disk was developed using Monte Carlo techniques for several classes of solar flares. The solar-flare polarimeter consists of a 30-cm-diam Be disk of about 1/3 of a scattering length thickness, which is surrounded by a cylindrical detector composed of six segmented panels of NaI scintillators, each coupled to 15 photomultiplier tubes. The instrument is sensitive to X-rays from 10 to 100 keV. For a class-M-2 solar flare observed for 10 sec from a balloon at an altitude of 150,000 ft, the minimum detectable polarization at the 99 percent statistical confidence level was found to be 1-6 percent over the energy range 20-100 keV.

Gotthelf, E.↗

NASA NTRS1990

In situ measurements of scattering from contaminated optics in the Vacuum Ultraviolet

NASA's In Situ Contamination Effects Facility has been used to measure the time dependence of the angular reflectance from molecularly contaminated optical surfaces in the vacuum ultraviolet. The light scattering measurements are accomplished in situ on optical surfaces in real time during deposition of molecular contaminants. The measurements are taken using noncoherent VUV sources with the predominant wavelengths being the krypton resonance lines at 1236 and 1600 angstroms. Detection of the scattered light is accomplished using a set of three solar blind VUV photomultipliers. An in-plane VUV BRDF (bidirectional reflectance distribution function) experiment is described and details of the on-going program to characterize optical materials exposed to the space environment is reported.

Herren, Kenneth A.↗

NASA NTRS1991

Optical Receiver Based On Luminescent Light Trapping

Experiment demonstrates feasibility of optical-communication receiver based on luminescent light trapping. Light-gathering element plate of transparent material impregnated with laser dye. Light from distant laser transmitter falls on plate and absorbed by dye molecules, which become excited and reradiate. Reradiated light confined within plate by total internal reflection as it propagates toward edge of plate. Light arriving at edge escapes from plate and detected by small, high-speed, high-gain photomultiplier tubes or other photosensitive devices. Simple, inexpensive, and accepts light from almost any angle. Receiver of this configuration supports reception of data at rate of 13 MHz and higher.

Perry, Joseph W.↗

NASA NTRS1991

Laboratory investigation of visible shuttle glow mechanisms

Laboratory experiments designed to uncover mechanistic information about the spectral and spatial characteristics of shuttle glow were conducted. The luminescence was created when a pulse of O atoms traveling at orbital velocities was directed toward NO molecules previously adsorbed to aluminum, nickel, and Z306 Chemglaz (a common baffle black) coated surfaces held at various temperatures. Spectral and spatial measurements were made using a CCD imaging spectrometer. Corroborative spectral information was recorded in separate measurements using a scanning monochromator and gated photomultiplier arrangement. The e-folding distance at several temperatures was calculated from images of the surface glow using the photometrics image processing capability of the imaging spectrometer. The e-folding distance was not altered as a function of incoming O beam velocity. The results are presented and the observations provide direct evidence that the visible shuttle glow results from recombination of oxygen atoms and surface bound NO.

Leone, A.↗

NASA NTRS1990

Fabry-Perot observations of comet Austin

Preliminary results of a program to observe Comet Austin (1990c1) from 16 April to 4 May and from 11 May to 27 May 1990 using the West Auxiliary of the McMath Solar Telescope on Kitt Peak, Arizona were presetned. The observations were made with a 15 cm duel-etalon Fabry-Perot scanning and imaging spectrometer with two modes of operation: a high resolution mode with a velocity resolution of 1.2 km/s and a medium resolution mode with a velocity resolution 10 km/s. Scanning data was obtained with an RCA C31034A photomultiplier tube and imaging data was obtained with a Photometrics LN2 cooled CCD camera with a 516 by 516 Ford chip. The results include: (1) information on the coma outflow velocity from high resolution spectral profiles of (OI)6300 and NH2 emissions, (2) gaseous water production rates from medium resolution observation of (OI)6300, (3) spectra of H2O(+) emissions in order to study the ionized component of the coma, (4) spatial distribution of H2O(+) emission features from sequences of velocity resolved images (data cubes), and (5) spatial distribution of (OI)6300 and NH2 emissions from medium resolution images. The field of view on the sky was 10.5 arcminutes in diameter. In the imaging mode the CCD was binned 4 by 4 resulting in 7.6 sec power pixel and a subarray readout for a field of view of 10.5 min.

Schultz, David↗

NASA NTRS1991

Bevalac studies of magnet Cerenkov spectroscopy

The attempt was made to identify the various contributions to the velocity resolution of Cerenkov detectors such as might be used in Astromag, to measure the magnitude of these contributions and assess their effect on the mass resolution of an isotope spectrometer for Astromag, and to perform Bevalac tests of magnet/Cerenkov spectroscopy. A first version of a new 5 in. photomultiplier tube was also tested that is designed for use in large magnetic fields.

Source record↗

NASA NTRS1991

Airborne lidar research

The planetary boundary layer (PBL) is the lowest layer of the atmosphere in contact with the Earth's surface. It plays an important role in atmospheric circulation and dynamics by influencing surface fluxes of moisture, heat, and momentum. The PBL is characterized by its turbulence structure. Organized convection within the PBL may generate gravity waves within the free troposphere. These waves can propagate vertically, modifying global circulation. Remote sensing of the PBL using a downward-looking lidar is providing new insight into dynamic processes of this important layer and its connection with wave generation. An airborne lidar is an ideal tool to study the PBL. The lidar is installed on the NASA Electra aircraft. It consists of a frequency doubled Nd:YAG laser aligned with a 40 cm diameter telescope. As the laser beam propagates downward from the aircraft toward the surface, it is scattered by the aerosols and molecules in the atmosphere. Generally, there is a sharp gradient of aerosol scattering associated with the PBL top, with high aerosol scattering from within the PBL, and generally very low scattering from the free atmosphere above. It is this gradient in aerosol scattering that is used to visualize the structure of the PBL. A small portion of the scattered radiation is collected by the telescope, filtered, detected by a photomultiplier, and digitized at 100 nsec rate. The horizontal resolution is typically around 13 m, using a 10 Hz laser and a nominal aircraft moves, the resolution of features in the atmosphere below the aircraft is about 15 x 13 m. Results from several studies are presented and discussed.

Melfi, S. Harvey↗

NASA NTRS1990

Active optical sensor technology

An account is given of the development status, performance capabilities, and prospective applications of lidar systems in earth remote sensing, as envisioned by researchers at NASA-Marshall, NASA-Goddard, NASA-Langley, and NASA-Wallops Island. Lidar systems can conduct measurements in research efforts concerned with wind fields, altimetry, ozone depletion, water vapor mixing ratios, temperature and pressure, phytoplankton chlorophyll fluorescence, forest folliage, and ice sheets. It is in all cases that lidar lasers be lightweight, compact, and efficient; most lasers need to be tunable. Detectors used range from photomultipliers to photodiodes.

Melfi, Harvey↗

NASA NTRS1991

SIGHT - A balloon borne hard X-ray telescope

The authors report on progress toward developing a large-area, high-pressure xenon gas scintillator for use in hard X-ray astrophysics. Proof test results for a low-mass pressure vessel are presented. The design of a high-voltage multiplier board operating inside the scintillation chamber is discussed. The development of tetrakis-dimethylamine-thylene (TMAE)-based proportional tubes for detecting primary scintillation in the xenon is described. Finally, Monte Carlo tests of a scheme to use conventional photomultiplier tubes are discussed.

Wilkerson, J.↗

NASA NTRS1991

Plastic scintillator block as photon beam monitor for EGRET calibration

The EGRET (Energetic Gamma Ray Experiment Telescope) detector has been calibrated at SLAC (Stanford Linear Accelerator) and, to a lesser degree, at the MIT Bates Linear Accelerator Center. To monitor the photon beams for the calibration, a plastic scintillator block, 5 cm x 5 cm in cross section, 15 cm in length, and viewed by a single photomultiplier tube, was used for the entire beam energy range of 15 MeV to 10 GeV. The design operation, and method of analysis of the beam intensity are presented. A mathematical framework has been developed to treat the general case of a beam with multiphoton beam pulses and with a background component. A procedure to deal with the fluctuations of the beam intensity over a data-taking period was also developed. The photon beam monitor is physically sturdy, electronically steady, simple to construct, and easy to operate. Its major merits lie in its sheer simplicity of construction and operation and in the wide energy range it can cover.

Lin, Y. C.↗

NASA NTRS1991

Coherent backscatter model for the unusual radar reflectivity of icy satellites

The coherent backscatter model is investigated experimentally by means of an analog to examine the nature of the radar reflectivity of icy satellites. The laboratory analog involves the examination of He-Ne laser light with a wavelength of 0.633 microns reflected from 0.497-micron polystyrene beads suspended in water. A photomultiplier and a polarizing filter are employed to observe the radar at phase angles greater than zero which are extrapolated to infer observation at zero phase angle. The polarization angles measured at optical frequencies are found to be equivalent to those observed in the radar data. The results suggest that the regoliths of the icy satellites consist of matrices of small complex refractive indices which contain scatterers separated by distances of the order of a wavelength. The experiment explains the high reflectivity of Jupiter's icy satellites which results in the observation of narrow opposition-effects peaks at optical frequencies.

Hapke, Bruce↗

NASA NTRS1992

Phosphor Scanner For Imaging X-Ray Diffraction

Improved optoelectronic scanning apparatus generates digitized image of x-ray image recorded in phosphor. Scanning fiber-optic probe supplies laser light stimulating luminescence in areas of phosphor exposed to x rays. Luminescence passes through probe and fiber to integrating sphere and photomultiplier. Sensitivity and resolution exceed previously available scanners. Intended for use in x-ray crystallography, medical radiography, and molecular biology.

Carter, Daniel C.↗

NASA NTRS1990

Contamination study

The time dependence of the angular reflectance from molecularly contaminated optical surfaces in the Vacuum Ultraviolet (VUV) is measured. The light scattering measurements are accomplished in situ on optical surfaces in real time during deposition of molecular contaminants. The measurements are taken using non-coherent VUV sources with the predominant wavelengths being the Krypton resonance lines at 1236 and 1600 A. Detection of the scattered light is accomplished using a set of three solar blind VUV photomultipliers. An in-plane VUV BRDF (Bidirectional Reflectance Distribution Functions) experiment is described and details of the ongoing program to characterize optical materials exposed to the space environment is reported.

Johnson, R. Barry↗

NASA NTRS1991

Investigation of the excited state iodine lifetime in the photodissociation of perfluoroalkyl iodides

An evaluation of prospective laser materials for a space-based solar pumped laser system over the past decade has resulted in the identification of the iodine photodissociation laser as that system best suited to solar-pumped high energy operation. The active medium for the solar-pumped iodine photodissociation laser is from the family of perfluoroalkyl iodides. These lasants have the general form C(n)F(2n + 1)I, often abbreviated as RI. These iodides are known to exhibit photodissociaiton of the C-I bond when irradiated by near UV photons. The focus was on the experimental determination of the lifetime of the excited iodine atom following photodissociation of C4F9I, and also to monitor fluorescence from the iodine molecule at 500 nm to determine if I2 is being produced in the process. Photodissociation is achieved using an XeCl excimer laser with an output wavelength of 308 nm. The XeCl beam is focused into the middle of a cylindrical quartz cell containing the lasant. The laser pulse is detected with a fast risetime photomultiplier tube as it exits the cell. Other aspects of the investigation are discussed.

Cobb, Stephen H.↗