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NASA NTRS1979

Wide-field electrographic cameras for imagery and spectrography at visual and middle-UV wavelengths

The use of a Kron electrographic detector for wide-field, narrow-band imagery of faint emission nebulosity in the near-UV and visual (3100-6000 A) wavelength interval is described. As an example of the photometric quality of the imagery and of the sensitivity of the instrumentation to diffuse, low-contrast objects, imagery of the Cygnus Loop supernova remnant in the high excitation forbidden line of Ne V 3426 A is presented. In addition, a program to develop electrographic detectors which use cesium telluride photocathodes for broad-band imagery and spectrography in the middle-UV (1650-3100 A) wavelength range is described.

Heckathorn, H. M.↗

NASA NTRS1980

Hydrogen production by photoelectrolytic decomposition of H2O using solar energy

Photoelectrochemical systems for the efficient decomposition of water are discussed. Semiconducting d band oxides which would yield the combination of stability, low electron affinity, and moderate band gap essential for an efficient photoanode are sought. The materials PdO and Fe-xRhxO3 appear most likely. Oxygen evolution yields may also be improved by mediation of high energy oxidizing agents, such as CO3(-). Examination of several p type semiconductors as photocathodes revealed remarkable stability for p-GaAs, and also indicated p-CdTe as a stable H2 photoelectrode. Several potentially economical schemes for photoelectrochemical decomposition of water were examined, including photoelectrochemical diodes and two stage, four photon processes.

Rauh, R. D.↗

NASA NTRS1980

Circular Scan Streak Tube Development

A streak tube having circular scan was designed, built and tested. Continuous circular scan, easily derived from out of phase sine waves applied to the conventional deflection plates, permits the timing of pulses traveling long baselines. At the tube's output a circular array of 720 elements is scanned to provide 30 to 40 picosecond resolution. Initial difficulties with electron bombarded silicon arrays were circumvented by using microchannel plates within the streak tube to provide the needed electronic amplification and digital sensitivity and coupling the 720 element arrays to the electron beam by means of a phosphor on a fiber optics. Two ceramic body tubes with S-20 photocathodes were tested and delivered.

Nevin, S.↗

NASA NTRS1979

Detector arrays for photometric measurements at soft X-ray, ultraviolet and visible wavelengths

The construction and modes of operation of the Multi-Anode Microchannel Array (MAMA) detectors are described, and the designs of spectrometers utilizing them are outlined. MAMA consists of a curved microchannel array plate, an opaque photocathode (peak quantum efficiency of 19% at 1216 A), and a multi-anode (either discrete- or coincidence-anode) readout array. Designed for use in instruments on spaceborne telescopes, MAMA can be operated in a windowless configuration in extreme-ultraviolet and soft X-ray wavelengths, or in a sealed configuration at UV and visible wavelengths. Advantages of MAMA include low applied potential (less than 3.0 kV), high gain (greater than 10 to the 6th electrons/pulse), low sensitivity to high-energy charged particles, and immunity to external magnetic fields of less than 500 Gauss

Timothy, J. G.↗

NASA NTRS1980

Circular-scan streak tube with solid-state readout

A circular-scan streak tube designed for use in a laser ranging system is described. Electrostatic focusing is used between the photocathode and a microchannel plate, and electrons from the microchannel plate are proximity focused onto an output phosphor screen. Electron beam deflection is achieved by driving two orthogonal sets of deflection plate assemblies in phase quadrature at a frequency of 200 MHz. The light intensity in the output beam trace is measured by using a circular Reticon array of 720 photodiodes, which is fiber-optically coupled to the output phosphor screen of the tube. Sample measurements of frequency-doubled Nd:YAG laser-pulse waveforms are given. Also the output beamwidth has been measured at the 200-MHz deflection frequency. The results suggest a limiting resolution of 33 psec for the circular-scan streak tube used for these tests.

Johnson, C. B.↗

NASA NTRS1981

Development and testing of 2-dimensional photon counter

The development of a commercially available two dimensional photon counter into an operational system for speckle imaging of astronomical objects is described. The system includes digital recording for field observations. The counter has a bialkali photocathode with a field size of 18 by 18 mm over which it resolves about 100 by 100 pixels. The system records photon positions as 16 bit words at rates up to 14,400 per second. Field tests at observatories verifying the operation of the system are described.

Source record↗

NASA NTRS1979

Space Telescope digicon technology

The objective of this program was to develop the technology and construct a number of tubes conforming to the chosen configuration. A total of ten starts were made and ten tubes went through to test. Of the ten tubes three were CsI on LiF, six were CsTe on MgF2 and one was KNaCsSb on SiO2. All three faceplate crystals sealed successfully using indium as the sealant. In addition, a number of test seals were made and two photocathode sample runs were made. The tasks E-field, faceplate, anti-corona and electron optical analysis were actively pursued and the results integrated into the BASD HRS project.

Alting-Mees, H. R.↗

NASA NTRS1980

Discovery of intrinsic linear polarization in SS433

Observations of variable linear polarization in the optical range in the unique radio and X-ray source SS 433, which is characterized by moving emission lines in its visible and near-IR spectra, are reported. The observations were made with an unfiltered GaAs photocathode covering the spectral region 3000-9000 A, with a passband characteristic wavelength near 7000 A. Measurements reveal the presence of both a long-term and a very short time-scale variation in linear polarization in the continuum and in H-alpha, which indicate that a substantial fraction of the polarization is intrinsic to SS 433 and not produced in the interstellar medium. It is suggested that the most likely source of polarization in the optical continuum is electron scattering, and constraints on models of SS 433 implied by the discovery of intrinsic polarization are considered.

Mclean, I. S.↗

NASA NTRS1981

Atmospheric emissions photometric imaging experiment /AEPT/ for Spacelab 1

The atmospheric emissions photometric imaging experiment (AEPI) to be flown on Spacelab 1 is designed to study faint natural and artificial atmospheric emission phenomena. Optical emissions are imaged in the region 2150 A to 7320 A using a television system consisting of two optical channels, one wide-angle and one telephoto. The detection system is an image-enhanced SEC vidicon. A third optical channel images onto the photocathode of a microchannel plate photomultiplier tube that has 100 discrete anodes. Photons are counted for each discrete anode, providing a direct measure of the luminosity of an object viewed by the TV telephoto lens, albeit with low spatial resolution. The AEPI detector is mounted on a two-axis gimbal comprised of a Modified Apollo Telescope Mount Star Tracker (MAST), which provides experiment pointing over a 40-deg x 80-deg range, exclusive of restrictions due to the proximity of other experiments. The pointing stability is 1 arcmin with respect to the spacecraft coordinate system for an exposure of 1 second. The tracking capability is 3.5 deg/s with a stability of 1 arcmin. The detector and pointing system are located on the Spacelab pallet. The experiment is controlled by stored programs resident in the Dedicated Experiment Processor located in the Spacelab module.

Sandie, W. G.↗

NASA NTRS1981

Lyman-alpha fluorescence from hydrogen photofragments of CH4 and H2O

The process of H-Lyman-alpha fluorescence produced through photodissociation of CH4 and H2O provides an example for the usefulness of the detection of fluorescence of dissociation fragments as an aid in identifying some high lying Rydberg states. In the first experiment reported, an electron storage ring synchrotron radiation source was used. The fluorescence produced was detected with a solar blind photomultiplier and a Cs photocathode with a spectral sensitivity in the wavelength range from 1050 to 1950 A. In the second experiment considered, an intense atomic line source was employed.

Wu, C. Y. R.↗

NASA NTRS1982

Low noise imaging photon counter for astronomy

The characteristics and performance of a Ranicon photon-counting system combined with digital tape recording are described. The most important features are a bialkali photocathode response over 256 X 256 digital pixels, with approximately 100 X 100 resolvable pixels at 50% MTF, a dead time of 16 microsec/count, a maximum recordable count rate of 14,400/sec, and a background of less than 1 count/digital pixel/h. A video cassette recorder serves for the digital recording which retains the temporal sequence of the registered photons. Astronomical applications will include low light level quantitative imaging and speckle imaging.

Mertz, L.↗

NASA NTRS1982

High-resolution imaging with a two-dimensional resistive anode photon counter

A method to achieve high spatial resolution readout of individual photoelectron events using microchannel plates and a resistive anode is presented. A clamped pair of microchannel plates is used, followed by a gap and a clamped triplet of microchannel plates in cascade to achieve a high stable electron gain of 3 x 10 to the 7th. The gain allows the position determination of each photoelectron event with a very high signal-to-noise ratio. A model consisting of a windowless vacuum-ultraviolet image sensor is presented to demonstrate 500 x 500 pixel images of 50 micron FWHM over a 25-mm circular field of view. The detector offers sufficient speed, sensitivity and resolution for a variety of applications, and the mount design is compatible with planar, remotely-processed, proximity-focused photocathodes.

Firmani, C.↗

NASA NTRS1982

Rocket-borne instrument with a high-resolution microchannel plate detector for planetary UV spectroscopy

A telescope-spectrograph employing a photon-counting microchannel plate (MCP)-CODACON detector has been built, tested, and flown on a sounding rocket. The detector uses a curved-channel MCP proximity focused onto a coded anode array of 1024 channels spaced 25.4-mm center to center. High quantum efficiency is obtained by depositing a cesium iodide photocathode on the front surface of the MCP. The instrument has obtained an ultraviolet spectrum of Jupiter with a spectral resolution of 8 A, which is higher than that of any previously reported observation in this wavelength range.

Mcclintock, W. E.↗

NASA NTRS1982

Images of the future - Two decades in astronomy

Future instruments for the 100-10,000 A UV-wavelength region will require detectors with greater quantum efficiency, smaller picture elements, a greater wavelength range, and greater active area than those currently available. After assessing the development status and performance characteristics of vidicons, image tubes, electronographic cameras, digicons, silicon arrays and microchannel plate intensifiers presently employed by astronomical spacecraft, attention is given to such next-generation detectors as the Mosaicked Optical Self-scanned Array Imaging Camera, which consists of a photocathode deposited on the input side of a microchannel plate intensifier. The problems posed by the signal processing and data analysis requirements of the devices foreseen for the 21st century are noted.

Weistrop, D.↗

NASA NTRS1982

The phototron: A light to RF energy conversion device

The phototron, a photoelectric device that converts light to radio frequency energy, is described. It is a vacuum tube, free electron, device that is mechanically similar to a reflex klystron with the hot filament cathode replaced by a large area photocathode. The device can operate either with an external voltage source used to accelerate the photoelectrons or with zero bias voltage; in which case the photokinetic energy of the electrons sustains the R.F. oscillations in the tuned R.F. circuit. One basic design of the phototron was tested. Frequencies as high as about 1 GHz and an overall efficiency of about 1% in the biased mode were obtained. In the unbiased mode, the frequencies of operation and efficiences are considerably lower. Success with test model suggests that considerable improvements are possible through design refinements. One such design refinement is the reduction of the length of the electron flight path.

Freeman, J. W.↗

NASA NTRS1983

Electron-bombarded CCD detectors for ultraviolet atmospheric remote sensing

Electronic image sensors based on charge coupled devices operated in electron-bombarded mode, yielding real-time, remote-readout, photon-limited UV imaging capability are being developed. The sensors also incorporate fast-focal-ratio Schmidt optics and opaque photocathodes, giving nearly the ultimate possible diffuse-source sensitivity. They can be used for direct imagery of atmospheric emission phenomena, and for imaging spectrography with moderate spatial and spectral resolution. The current state of instrument development, laboratory results, planned future developments and proposed applications of the sensors in space flight instrumentation is described.

Carruthers, G. R.↗

NASA NTRS1982

Space Schmidt telescope

The complete survey takes in 3627 fields, each 4.87 deg in diameter, arranged in a hexagonal pattern superimposed on the celestial equatorial coordinate system. The declination bands are spaced every 3 deg, 20 min. The optical instrument is a folded all-reflecting Schmidt system with an aperture of 0.74 m, a focal length of 2.0 m (f/2.7), a circlar field with a diameter of 4.87 deg, and a limiting image diameter of less than 2 arcsec over the entire field. The detector is an electrographic camera having a photocathode diameter of 170 mm. In discussing the telescope structure, it is pointed out that the optical support system is to be of graphite-epoxy construction. The focal tolerance (the most critical optical tolerance) is to be + or - 12 microns. Regarding contamination control, it is expected that with appropriate design it will be possible to operate in sunlight for observations in a restricted portion of the sky, at least more than 90 deg from the sun, depending on the geometry and reflectivity of the platform or spacecraft configuration.

Wray, J. D.↗

NASA NTRS1982

Texas Instruments' virtual phase charge-coupled device (CCD) imager operated in the frontside electron-bombarded mode

The present investigation is concerned with the suitability of the virtual phase CCD imager for frontside detection of electrons up to 25 keV. The investigation has the objective to determine if the imager can be used in the frontside mode with a photocathode to detect very low light levels in astronomical applications, the ultimate goal being individual photon detection. It is found that the standard virtual phase imager will function properly over an extended period at low levels of 20 kV electron irradiation consistent with photon counting applications. The imager can detect individual primary electrons with nearly 100 percent efficiency. However, further studies are needed to determine the mechanisms for the flat band shifts so that the imager design may be modified to eliminate or at least reduce them.

Everett, P.↗