Triggered-avalanche photon counting, recently demonstrated in cooled Silicon photodiodes, should also work in any other intrinsic semiconductor material. As carrier-trapping problems are solved, photon-counting diodes and arrays should become available throughout the mid-infrared. Possible applications to astronomical instruments abound.

Advanced infrared detector and detector array technology is being developed and characterized for future NASA space astronomy applications. Si:Bi charge-injection-device arrays have been obtained, and low-background sensitivities comparable to that of good discrete detectors have been measured. Intrinsic arrays are being assessed, and laboratory and telescope data have been collected on a monolithic InSb CCD array. For wavelengths longer than 30 gym, improved Ge:Ga detectors have been produced, and steps have been taken to prove the feasibility of an integrated extrinsic germanium array. Other integrated arrays and cryo-genic components are also under investigation.

Low temperature tests of the G. E. 32x1 and 32x32 InSb CID arrays were carried out to evaluate their potential for use in infrared astronomical instruments. The tests revealed that the arrays could be operated at⪅20°X. with dark currents low enough that integration times of up to 1 hour would be possible. Responsivities up to 1.8 AN for the linear array and 0.4 AN for the area array. at 3.6 microns were observed dropping to 0.9 AN and 1.2 AN respectively at 4.7 microns. The linear array exhibited a troublesome response lag at low flux levels which, limits its usefulness and the area array usefulness will be limited by its higher noise level.

The Canada-France-Hawaii Telescope Co. two-dimensional array of infrared detectors has been applied for the first time to the stellar speckle interferometry technique. Preliminary results are presented.

Detector Johnson-noise-limited operation of InSb photovoltaic detectors has previously been reported. Typically, a cooled, dual JFET is used to amplify the signal before passage to subsequent amplification electronics. Most configurations employ an arrangement in which the cooled JFET's and feedback resistors are packaged and cooled separately from the detector element. This can result in large amounts of pickup noise from the observatory environment. With the advent of higher quality InSb photodiodes the ultimate NEP's possible depend more upon the investigator's ability to shield the detector and initial amplification stage from outside sources than on detector properties. In this paper we describe InSb detector-hybrid configurations in which the detectors, dual JFET dies, and feedback resistors are mounted closely together in the same hybrid flatpack. This allows complete shielding of detector and initial-stage amplification electronics. With typical 0.25 mm and 0.5 mm detectors and R_oA products near 5 x 10⁶ Ω-cm2, theoretical-limit NEP's of approximately 5 x 10^-16 W/(Hz)1/2 at 77 K are obtained.

Stepper motors operating at temperatures below 16°K may be used extensively in high sensitivity infrared instruments. However, the behavior and reliability of Hators operating at cryogenic temperatures have not been extensively characterized. We summarize our experimental investigation of stepper motor performance in vacuum at LN₂ (76^oK) and LHe (4^oK) temperatures. Initial tests demonstrated that stepper motors fail at LN₂ temperatures due to differential thermal contraction arising from the use of different metals in the motor construction. The motors were then modified to compensate for thermal contraction differences and one of the modified motors was successfully tested at LHe temperatures. It ran normally for 112 hours without any significant degradation either in its voltage waveform pattern or with any significant differences between its pretest and post-test holding torques. These test results may aid cryogenic instrument designers who utilize electro-mechanical devices in planned facilities such as the Shuttle Infrared Telescope Facility (SIRTF).

We have developed a compact, stable, single-stage intensified photodiode array detector for photon-counting, far ultraviolet astronomy applications. The intensifier, constructed by ITT, employs a saturable, 'C'-type MCP (Galileo S. MCP 25-25) to produce high gain (≈10⁶) pulses with a narrowly peaked pulse height distribution. A high efficiency, opaque CsI photocathode is coated directly onto the MCP input surface. The P-20 output phosphor exhibits a very short (≈10μs) decay time, due to the high current density of the electron pulses. We are currently coupling this intensifier to a Reticon RL1024-SF self-scanning linear photodiode array, with 1024 - 25μ x 2.5 mm tall diodes. This device has a fiber optic input window which allows direct, rigid mechanical coupling with minimal light loss. Initial testing has been accomplished using the driver circuitry supplied by Reticon, followed by a 4 bit ADC and DMA interface with an HP 9845 desktop computer. The array was scanned at a 250 KHz pixel rate. The detector exhibits more than adequate signal-to-noise ratio for pulse counting and event location. Event location algorithms that compute the pulse centroids to 1/2 diode width accuracy have yielded detector spatial resolution limited by the MCP channel spacing (32μ). Designs for a fast amplifier/clock driver circuit and a bit-slice microprocessor device for real-time photon event location are now being implemented. We anticipate that the short phosphor decay time and use of a fast, dedicated microprocessor for event location will permit rapid scan speeds and hence large dynamic range. The small physical size, stability, insensitivity to environment, low bias voltage, wide dynamic range and independent pixel properties combine to make this detector very suitable for space flight astronomy applications.

One of the methods of enhancing the blue and UV sensitivity of a silicon array is the Viehmann technique of coating it with a thin plastic film which has been made fluorescent by the addition of one or more laser dyes. This report describes the preparation of such films and the performance characteristics of cooled silicon CIDs coated with them.

A computer-controlled intensified television detector, sensitive to Photons between 1μ and 0.05Å, has been built for a wide range of applications, including X-ray astrophysics and observational astronomy. A digitally controlled intensified SIT vidicon camera generates a high resolution image which is digitally processed in real time and integrated in a large, high-speed memory system. The camera electronics can also accommodate CCD arrays or any other raster readout detector or camera. A thin scintillator or phosphor convertor deposited on a fiber optics faceplate is used for X-ray and vacuum ultraviolet applications. Active areas from 4 to 80 mm square and larger can be selected and easily changed. For rates of up to 104 or 105 events/sec the centroid of each event can be computed, while rates of up to 10¹²/sec can be accommodated by continuously digitizing and storing the video signal at each pixel. The camera scan rates and formats and the size and location of the scanned and gated areas of the target are under software control. The data acquisition and processing parameters and operating modes are also under software control. Interactive control and monitoring allow the detector system to be optimally configured for each anplication. Any array size un to 4000x4000 pixels can be selected. The spatial resolution depends on the active area, operating mode, and TV tube resolution, and ranges from 10μ to 200μ. A typical low-cost 25 mm system has a resolution of about 30μ in the photon counting mode and 100μ in the A/D mode. The memory system accommodates up to 16M words of 12 to 24 bits, and can display the integrated image during and after accumulation. Modular construction allows the detector system or any of its subsystems to be easily duplicated at a low cost.

Their large dynamic range (> 10⁴), high quantum efficiency (QE ≈, 50%), and large format 103x103 pixels) make charge coupled devices (CCD) ideally suited to the high signal to noise demands of differential imaging (e.g. polarimetry, narrow-band photometry, fast-chopping ultra-deep imaging). However, if the CCD is read once for every phase in the chopping cycle, the readout noise is comparable to the signal in most astronomical applications (σ ≈ 30 RMS electrons/pixel), F ≈ 10 electrons/pixel -s, chopping rate ≈ 0.1 Hz). We describe herein a technique which allows long integration periods between readouts (t ≈ 10³s) together with moderate chopping rates (0.1 - 1.0 Hz). During each phase of a differential chopping cycle, one set of charge images is shifted to the center of the chip, which is light sensitive. At the same time the other set(s) of charge images is shifted under one of two masked areas which serve as charge-storage sites. Since the vertical shifting between phases can be accomplished in much less time than the typical exposure per phase, there is negligible image smearing and, therefore, no shuttering is required except during readout. In order to achieve efficient charge transfer efficiency in both the normal and reversed vertical directions, three phase or four phase vertical electrode structures are required. For a given light level and chopping rate the performance of this technique is limited primarily by the readout noise and the vertical charge-transfer inefficiency (η ≈10^-4 per shift). If, in order to achieve sufficient signal to be photon-noise-limited (S > σ²/η, many transfer cycles are required between readouts, the charge transfer inefficiency will diffuse the accumulated charge images along the,vertical columns. The diffusion time scale in terms of vertical shifts is ≈ 0.5 λ_o²'in where ^λ_o is the intrinsic image scale in picture elements (pixels). The figure of merit for a given CCD is, therefore, proportional to QE/σ²η. A more detailed discussion of the theoretical performance of the technique, including the effects of poor charge-transfer efficiency at low light levels, is presented. We also present laboratory and astronomical data obtained with this technique using the Steward Observatory CCD Camera and the 2.3m telescope on Kitt Peak.

The effect of readout noise from CCD output stages can be reduced by paying attention to the design of the external circuitry. Techniques are described, with particular reference to GEC devices, for the reduction of capacitance and improvement in the gain of the output stage. The characteristics of several correlated double sampling schemes are reviewed and values for the output noise are predicted.

A liquid nitrogen cooled CCD camera utilising the RCA 53612 thinned CCD is described. It was constructed primarily for direct imaging at the prime focus of the Anglo Australian Telescope and is now installed as a common user instrument. The camera head, drive electr-onics and microprogrammable controller are briefly described. The camera has been designed to accommodate other CCD chips with minimum modification: many operating modes are available under software control. Operating characteristics and some astronomical results are presented.

A fully portable self-contained charge-coupled device system has been constructed for shared use with the Galileo Project Imaging Team. The detector currently incorporated in the system is a Texas Instruments (TI) 500x500 three-phase CCD that has been thinned to operate in the backside illuminated mode. The detector and camera mainframe electronics were provided by the Jet Propulsion Laboratory (JPL). We constructed the support electron-ics and control interfaces necessary to operate the mainframe. We also integrated the data system, which is built around a DeAnza Visacom VC-5000 Image Processor with an imbedded LSI-ll minicomputer. The capability to do image processing in real-time at the telescope has proved to be extremely valuable. The overall system read noise has been measured at 25 electrons. Full-well capacity is 40,000 electrons. Some results from laboratory tests and initial observing runs at the Mauna Kea 2.2-m telescope are presented.

Because of the considerable interest in a space probe mission to a near-Earth asteroid, we are developing the techniques necessary for a ground-based telescopic survey to increase the known number of such objects. The faintness (apparent magnitude = 18 to 21) and angular speed (up to 1 arcsec per second) make the techniques of detection different from the photographic and vidicon methods currently being used to observe distant asteroids and artificial satellites. The geometric stability and regularity of the pixels in a CCD will allow better measurements of relative positions of stars and asteroids than are possible with film or vidicons, but to take full advantage of CCD's we have considered the effects of the earth's atmosphere, the image scale (arcsec/pixel), the spectral bandpass, the exposure time, the detective quantum efficiency of the CCD, the direction of asteroid motion with respect to the CCD channel boundaries, and the time between the two scans from which the asteroid motion is to be inferred. Two interesting tradeoffs are (i) the high signal-to-noise ratio of a broad spectral bandpass versus the sharper images due to the small atmospheric dispersion associated with a narrow bandpass and (ii) the greater sensitivity to motion resulting from a long time interval between the two scans versus the greater changes of atmospheric dispersion, seeing, and anomalous refraction over long time intervals.

This paper discusses the development of the GSU speckle camera system. Primary consideration was given to stability, reliability, observing efficiency, portability and sensitivity. The optical and mechanical design allows the high gain, two-dimensional detector to be used for both field acquisition and speckle recording. The detector package consists of a proximity focus, dual microchannel plate intensifier, fiberoptically coupled to a two-dimensional CCD operating at standard video rates. The camera head control electronics are based on a 6809 microprocessor. The microprocessor based electronics controls the various motor driven optical components for the two observational modes (speckle and acquisition), adjusts the atmospheric dispersion compensation elements, positions the narrow bandpass optical filters, controls the field integration time, controls the number of recorded data fields per object and handles various other house-keeping functions. A separate micro-computer stores the observing program on floppy disks and calculates the position settings for the atmospheric dispersion compensation elements. The raw observational data is recorded, real time, on a special video cassette recorder. The video tape is positioned by stepper motors and tape position is servo controlled relative to the video read heads to maximize stability and minimize guard band noise in the "still frame" read mode. The present system concept incorporates a near real time digital autocorrelator for processing the video taped data.

A modified Fairchild CCD-221 detector has been installed in the coude spectrograph of the KPNO 2.1-m telescope for use in obtaining high dispersion stellar spectra. The system can be used to obtain spectra in the wavelength region from 4900 - 9900 A with resolutions ranging from 70 - 470 mA. The instrument system features a newly designed "universal" dewar, which may be used to mount the CCD in most any orientation, and an integrated observing and data reduction software system, which automates most of the routine data processing steps.

We have previously reported on the conceptual design and predicted performance of a new type of dedicated astronomical telescope to be used for a deep photometric survey for galactic and extragalactic variability and polarization. Data derived from this survey will be useful for a wide variety of astronomical investigations including the definition of a complete sample of QSOs, based on their variability and nonstellar colors, the detection of supernovae on the rising branch of their light curves, and the determination of the super-nova production rate as a function of galaxy color, morphology and redshift. The telescope we are producing to accomplish this survey is a transit instrument. It will incorporate a 1.8 m primary mirror of very high quality, fabricated as part of the program to develop the Space Telescope mirror technology, and, as its detectors, two RCA CCDs (512 x 320 x 30 micron pixels) used in the time-delay and integration (TDI) mode. By means of a dichroic beamsplitter the two CCDs view the same region of the sky, subtending about 8.2 arcminutes in declination. The effective integration time on the sky using this technique is about one minute, resulting in a faint limiting magnitude of about 22 per night. The data from the digitized strip of sky is recorded and analyzed in real-time for specific events such as supernovae. The CCD/transit technique has been demonstrated using the Steward Observatory (SO) 2.3 m telescope with the drive switched off. The results of this demonstration are shown and discussed. We report on progress in all aspects of the CTI development including the design of the transit telescope, which is optimized for wide-field, seeing-limited imaging. In particular, we describe a two-mirror field corrector system which realizes the potential image quality of the high precision primary mirror over a wide field and over the wide spectral bandpass of the CCDs.

A new procedure has been developed of using a Charge-Coupled Device (CCD) that entirely eliminates the need for flat field calibration exposures and therefore avoids the limitations inherent in conventional flat fielding methods. This paper describes the procedure, its advantages and disadvantages and the data processing steps that are needed. Examples of images at various stages are given as are the first results of background galaxy counts to an equivalent J magnitude of about 25^m6.

The Texas Instruments' Virtual Phase CCD imager has been successfully operated in the frontside electron-bombarded mode. The entire active area of the imager was covered with 130 nm of thermally grown gate oxide while only the clocked half of each pixel was addi-tionally covered with a 500 nm polysilicon electrode. No protective overcoat was grown over the imager. A 20 kV electron beam was focused onto the imager to a total dose in excess of 120,000 primary electrons per pixel. Both the parallel and serial clocks were operated between -15 V and +2 V throughout, and no adjustment in any of the operating parameters was required. However, flat band shifts on the order of 2 V were detected. Single primary electron events were clearly detected with a signal-to-noise ratio exceeding 10. In excess of 90% of the secondary charge generated by a primary event was collected in a single pixel. The standard virtual phase imager with only the protective overcoat deleted can be used with a photocathode in the electron-bombarded mode for observing low-to-moderate light levels and can act as a true photon counter.

An infrared staring mode imaging sensor was designed to operate with the NASA Infrared Telescope Facility (IRTF) at Mauna Kea, Hawaii. The sensor has a 0.5 arc sec spatial resolution over a 10 arc sec field and is matched to the f/35 focal ratio of the telescope. The focal plane device is a back-side illuminated Schottky infrared charge-coupled-device (IRCCD) mosaic with a photoresponse from 1 to 5 μm. Astronomical observations are reported at 2.2 μm where the IRCCD auantum efficiency is substantially greater than values normally reported for the 3.4 to 4.2 μm thermal imaging band.

The newly designed Zeiss spectrophotometers cover the total spectral range used in ground based astronomy. The first instrument for 1-5 pm contains an In:Sb photovoltaic detector and the second instrument for 5-14 pm a Si:Ga photoconductor. The instruments are nearly identical in their configuration. They are independent of liquid cryogens due to their closed cycle refigerator system. The internal cooled field optics has been optimized for minimum thermal background radiation. The medium spectral resolution of 50 - 100 is achieved by circular variable filters. The instruments fully operate under microprocessor control which provides rough data eva-luation (Lock In procedure) as well as data storing.

A grating spectrometer, designed to illuminate an array of 122 InSb photodiodes with minimum aberrations and maximum speed, has been constructed. The instrument will be used on the 5 meter Hale telescope at Palomar Observatory, and is easily adaptable to telescopes of various focal ratios. A resolving power of 100-1000 can be obtained at wavelengths between 0.6 pm and 5 pm with remotely interchangeable gratings. The spectrometer is sufficiently compact to fit on the 8-inch work surface of a commercially available dewar, and uses simple on-axis spherical and paraboloidal optical elements. The camera mirror produces an f/2.5 beam which, with the 0.2 mm detectors, allows a 3" focal-plane aperture on the 5 meter telescope. All rays fall within a 100 μm blur circle at all points along the array. Distortions have been corrected with a tilted field flattening lens in front of the detector.

A 128-element InSb linear detector array read out with a field effect transistor (FET) multiplexing scheme has been developed at the Jet Propulsion Laboratory: State-of-the-art NEP, uniform response, on-detector charge integration, and very low focal plane heat load compared to that of discreet detector arrays allows this type of array to open new possi-bilities for spaceborne near-infrared imaging spectrometers. Large number of cooled detector elements are feasible with the new technology, making it practical to design sensitive spectrometers even for spinning spacecraft where simultaneous wavelength coverage is necessary to avoid confusion of spatial with spectral variations.

The Near-Infrared Mapping Spectrometer (NIMS) is one of the science instruments in the Galileo Mission, which will explore Jupiter and its satellites in the late-1980's. The NIMS experiment will map geological units on the surfaces of the Jovian satellites, characterize their mineral content; and for the atmosphere of Jupiter, investigate cloud properties and the spatial and temporal variability of molecular abundances. All the optics are gold-coated reflective and consist of a telescope and a grating spectrometer. The balance of the instrument includes a 17-detector (silicon and indium antimonide) focal plane array, a tuning fork chopper, microprocessor-controlled electronics, and a passive radiative cooler. A wobbling secondary mirror in the telescope provides 20 pixels in one dimension of spatial scanning in a pushbroom mode, with 0.5 mr x 0.5 mr instantaneous field of view. The spectral range is 0.7 - 5.2μ; resolution is 0.025μ. NIMS is the first infrared experiment to combine both spatial and spectral mapping capability in one instrument.

An ultra-high resolution diode laser heterodyne spectrometer for observational and laboratory use has been developed for operation between 7.5 and 8.5 microns. The local oscillator is a PbSe tuneable diode laser kept continuously at operating temperatures of 12-60 K using a closed-cycle cooler. The laser output frequency is controlled and stabilized using a high-precision diode current supply, constant temperature controller, and a shock isolator mounted between the refrigerator cold tip and the diode mount. Reflecting optics are used whenever possible to minimize losses from internal reflection and absorption, and to eliminate chromatic effects. The spectrometer is used with a 64-channel RF spectral line receiver for a resolving power of 1.5 X 10° and an IF coverage of 1600 MHz. Heterodyne observations of the sunspot spectrum near 1200 cm1 have revealed fully resolved absorption features in the v = 1-0 and v = 2-1 rotation-vibration bands of silicon monoxide. The instrument has also been used for continuum observations of the infrared object IRC+10-216 as well as for measurements of terrestrial N₂O, 0₃ and CH₄.

We describe the design and use of an infrared Fourier transform spectrometer which has been used for observations of laboratory, stratospheric, and astronomical spectra. The spectrometer has a spectral resolution of 0.032 cm and has operated in the mid-infrared (12 to 13 microns) as well as the far-infrared (40 to 140 microns), using both bolometer and photoconductor cryogenic detectors. The spectrometer is optically sized to accept an f/9 beam from the multi-mirror telescope (MMT). The optical and electronic design are discussed, including remote operation of the spectrometer on a balloon-borne 102 cm telescope. The performance of the laser-controlled, screw-driven moving cat's-eye mirror is discussed. Segments of typical far-infrared balloon flight spectra, lab spectra, and mid-infrared MMT spectra are presented. Data reduction, interferogram processing, artifact removal, wavelength calibration, and intensity calibration methods are discussed. Future use of the spectrometer is outlined.

A spectrometer optimized for measurement of narrow spectral features in the 10 pm atmospheric window has been constructed and used for astronomical observations. The instrument consists of a LN₂ cooled, piezoelectrically scanned, Fabry-Perot interferometer and a LHe cooled grating monochromator and Si:As photoconductive detector. The Fabry-Perot has been used with a free spectral range of 3-10 cm^-1 and a resolution of 0.07-0.3 cm^-1. The grating, which isolates a single order of the Fabry-Perot, has a resolution of typically 2 cm^-1 with an entrance aperture corresponding to 6" on a 3m telescope. The system sensitivity, which is photon shot noise limited, is 2x10^-14WHz-1/2 , including all losses in the spec-trometer, telescope, and atmosphere, and due to chopping. The instrument can be used as a scanning spectrometer to measure line shapes and fluxes or as a monochromator to allow emission-line mapping of nebulae. Astronomical applications have included observations of the motion and distribution of the ionized gas in the Galactic center and first detections of H₂ S(2) at 12.28 μm and H I Humphreys a at 12.37 μm.

A high straylight cryogenic telescope has been developed to provide spatial definition for a Fourier Transform Spectrometer. The system is all-aluminum and uses off-axis super-polished parabolas with an advanced baffle system for high straylight performance at cryogenic temperatures. The all-reflective optical system is capable of better than 0.1 milliradian resolution over a half a degree field-of-view. The brazed mechanical structure is integrated with a careful thermal design, allowing the optics to maintain liquid helium region temperatures without the use of thermal straps. The telescope has been tested for stray light, optical performance at cryogenic temperatures and against shuttle environmental requirements. A discussion of the design analyses, test rechniques and measured results will be included in the paper.

A powerful high resolution spectrometer has been developed, and is installed at the Coude Focus of ESO's 3.6 m telescope. It can also be fed by a 1.4 m auxiliary telescope dedicated to the instrument. With this latter telescope magnitude 10 stars can be observed at a resolving power of 100.000 and with a good instrumental profile. The CES also features a single channel scanner mode which can attain a resolving power of 300.000 with an extremely high spectral purity.

The 1.4 m Coude Auxiliary Telescope (CAT) is designed for spectroscopy and will be used whenever the ESO 3.6 m telescope is not used in coude focus. The telescope is designed as an Alt-Alt mounting, which gives mechanically an attractive and inexpensive structure without any need for big counterweight systems. The optical configuration is of the Nasmyth type with a flat moveable third mirror mounted in the center of the telescope. The main mirror has a f-ratio of f/3. The exit f-ratio is f/120. The telescope is completely remote controlled, as it is placed in a tower separated from the operating center. Guiding is performed via a low light level TV-camera on the slit of the Coude Echelle Spectrograph (CES). The drive systems for the two axes in the Alt-Alt mounting are identical. They are of the direct drive type, with a torque motor, tacho generator and encoder connected directly to the shaft without any reduction gear. The positioning system is based to a great extent on microprocessors.

A "sun as a star" spectrometer is described which measures the variability of the core of Ca II 3933Å relative to the nearby continuum at 3953Å. The system is capable of 0.001% photometry but differential atmospheric extinction over the 20Å bandpass limits detectivity to 0.02%.

The 4 metre, F/2.8, Ritchey-Chretien (R-C) telescope of Kitt Peak National Observatory (KPNO) is equipped with a "grism" (grating+prism) located after the 3-element Wynne R-C corrector to provide slitless spectra which are, unfortunately, restricted to a 30 arcmin field at the prime focus although its corrector is designed for a 50 arcmin field. The performance could be improved if the grating were located a maximum distance from the focal surface, preferably on the last element of the corrector: a grating-on-lens or "grens". The last surface of the corrector lens should be made flat if it is to be used as a blank for a transmission grating. Optical parameters are given for such a corrector having a slightly larger diameter but with a flat last surface for a 4 metre, F/2.8, R-C telescope. For use as a grens this third element must be interchanged with a wedged element with the transmission grating deposited thereon. Compared with the grism, the field increases to 50 arcmin with the grens, the spectral resolution improves at the extremes of the wavelength region and the transmission increases because only three instead of five elements are used. Even better performance could be achieved if, instead of being R-C, the telescope were Classical because the field could be increased to 1 degree and the spectral resolution improved with a modestly enlarged corrctor the diameter of which need not be larger than the modified Wynne Classical corrector of the 3.6 metre, Classical, F/3.8, Canada France Hawaii Telescope (CFHT). By comparison, enlargement of the Wynne R-C corrector decreases the resolution. However, a new corrector design for R-C telescopes can equal the Classical performance but requires an unprecedentedly large triplet lens.

We report the first application of an aberration corrected, concave holographic grating to a stellar spectrograph for conventional astronomy with telescopes of moderate aperature. The spectrograph is comprised. of three modules: the first contains field. viewing optics and physically interfaces the instrument with the telescope; the second holds a comparison source and optics for f/ratio matcLing and slit viewing; and the last is a modified commercial spectrometer incorporating an optimized concave holographic grating. Astronomical dispersion is 160 Å/mm. Wavelength range is 3700 to 6600Å. Performance of the instrument is illustrated by spectra of MK standards.

The Faint Object Spectrograph of the Space Telescope will be able to obtain spectro-polarimetric data on faint astronomical objects. This is done by introducing a Wollaston prism and rotating waveplate behind the spectrograph entrance apertures. Fabrication of the polarimeter assembly has now been completed at the Martin Marietta Aerospace Co. in Denver, Colorado. Recent tests of the polarimeter and its optics have demonstrated that the device is capable of excellent performance. The magnesium flouride optical components of the polarimeter permit measurements of linear and circular polarization throughout the ultraviolet, down to Lyman a at 1216 Å. The mechanical stability and repeatability of the mechanism are demonstrated to yield position angles of the incoming plane of polarization to better than ± 0.5°, and we anticipate that measurements of the degree of polarization could be made to an accuracy of at least 0.1%. The accuracy for faint objects will depend on the integration times available for the observations, because of noise from photoelectron statistics. A 20-minute integration at 15th magnitude gives typically errors of 1% in each 100 Å wide spectral band.

The Faint Object Spectrograph (FOS) designed for use with The Space Telescope (ST), is currently preparing for instrument assembly, integration, alignment, and calibration. Nearly all optical and detector elements have been completed and calibrated, and selection of flight detectors and all but a few optical elements has been made. Calibration results for the flight detectors and optics are presented, and plans for forthcoming system calibration are briefly described.

We have built and operated an instrument to obtain simultaneous spectra of many objects in the field of view of the Steward Observatory 2.3m telescope. Short lengths of optical fiber are used to bring light from galaxy images at the Cassegrain focus of the telescope into a line along the spectrograph slit. This multi-fiber instrument has been dubbed the Medusa Spectrograph. This instrument is presently producing ≈ 100 spectra of galaxies down to m_v ≈ 17.5 per clear night. A brief description of the instrument and observing procedure is given here. We are also developing an improved version of the instrument to record spectra at a much higher rate. In this new instrument, called the MX Spectrometer, gains in efficiency will be obtained by remotely positioning the fibers under computer control and by correctly matching the output of the fibers to the spectrograph optics. Focal ratio degradation of the f/9 beam in the fibers is suppressed by sneeding up the beam with a SELFOC lens before it enters a smaller fiber. Since the outnut of the fibers is now approximately f/4, a large collimator is placed in the spectrograph to collect the light from the fiber array at the slit. A Charge Coupled Device will replace the image tube and photographic plate detector system. The CCD will allow sky subtraction, give increased dynamic range and will provide more accurate wavelength calibration because of the fixed format detector. We are currently testing a CCD behind the image tube with the Medusa system.

A preliminary design of a fiber-optics feed for the prime-focus spectrograph of the Hale telescope using computer controlled movable fiber has been completed and a test of a proto-type configuration carried out. The complete design will divide a 76mm square field into 10 strips and will place two movable fibers in each strip. The fiber pickups, which are moved by stepper-motor driven lead screws, may be placed anywhere in the strip subject to the limitation that they not pass each other. The prototype consisted of a single strip with two fibers operated with manual input to the stepper motors. In tests performed at the 5 meter Hale telescope in April of 1981 spec-tra of two bright 0 stars (B = 8.5 mag) separated by 5 arc minutes were photographed with a 3 minute exposure using a 1200 line/mm grating and unbaked 103a0 plates. The performance of the prototype configuration was within a factor of two of the unmodified prime-focus spec-trograph indicating a potential for a ten-fold increase in the effective utilization of the telescope for spectrographic survey work when fitted with the 20-fiber feed.

Simultaneous observation of several astronomical sources can be an effective way to increase the efficiency of telescope use. A description of the scheme currently in use at Kitt Peak, employing multiple entrance apertures to spectrographs and digital array detectors, is presented. Typical uses include surveying fields of faint objects for peculiar sources, and deriving radial velocities and/or spectrophotometry of stars or galaxies in clusters.

We describe the results of a series of high-resolution spectroscopic observations undertaken with a linear (1 x 1024)-pixel visible-light Multi-Anode Microchannel Array (MAMA) detector on the Coude spectrograph of the 2.2-meter telescope at the Mauna Kea Observatory and on the vacuum spectrograph of the McMath Solar telescope at the Kitt Peak National Observatory. In addition, we briefly describe the two-dimensional MAMA detector systems with (16 x 1024)-pixel, (24 x 1024)-pixel, and (256 x 1024)-pixel formats which are now being readied for use in a series of ground-based, balloon, and sounding-rocket observing programs.

We describe our plans to combine the High Angular Resolution Imager/Spectrometer on the 4-meter Mayall telescope at the Kitt Peak National Observatory and the (256 x 1024)-pixel Multi-Anode Microchannel Array (MAMA) detector system, developed at the University of Colorado, to produce a unique instrument for speckle spectroscopy. The pulse-counting detector system will provide distortion-free imaging and will time tag each spatially-resolved photon event with an accuracy of 100 ns. The Imager/Spectrometer will provide a spatial resolution of 0.07 arcsec orthogonal to the plane of dispersion and 0.18 arcsec in the plane of dispersion.

We are developing a new instrument for McDonald Observatory designed to allow measurement of stellar radial velocity variations to a precision of ± 1 m/s. The prime scientific use of the instrument will be a search for planets around other stars, but it will also be extremely useful for studies of binary stars and for analysis of stellar atmospheric motions including the more complex modes of pulsation now being discovered in the sun and a few other stars. A pair of ultra stable Fabry-Perot etalons, used in reflection, will im-pose a set of fixed reference absorption lines on the stellar spectrum before it enters the coude spectrograph of the McDonald Observatory 2.7m telescope. The spectrum, covering 1500 ⟨ at 0.132 Å resolution, will be recorded by the Octicon detector. The etalons and optical isolator system will be rigidly mounted in an evacuated, thermostated chamber to prevent movement of the interference orders exceeding the desired precision. A double cross-correlation technique will be used to measure the shift of stellar spectral lines will respect to the artifical absorption lines introduced by the Fabry-Perot orders. Calibration methods have been developed to measure any motion of the etalons which might occur.

Astronomy in the ultraviolet at wavelengths shortward of 1200 A is a largely unexplored field, but one which holds tremendous potential. Efforts to study this region have, to date, been largely frustrated by the poor reflectivity of mirror surfaces. We point out that grazing incidence optics can solve this problem. We show that grazing optical designs are exceedingly versatile at wavelengths longer than 100 A. We discuss the design of spectrographs using grazing incidence components and estimate their performance parameters. We present a design for a hypothetical space observatory which uses grazing optics to study the 100-1500 A region of the spectrum. It has very high throughput and operates in a variety of modes which have resolution from as low as 10³ (λ/ΔΒλ) to as high as 10⁵.

The International Ultraviolet Explorer (IUE) satellite is an astronomical observatory which has obtained more than 25,000 spectral images since its launch in January 1978. A 45 cm f/15 cassegrain telescope feeds two echelle spectrographs of resolution 10⁴ with intensified SEC vidicon detectors. Sources are placed for observation using small slews of the spacecraft after positional measurement by an image dissector. Optimum performance requires that the effects of the fluctuating thermal environment be considered in the acquisition and processing of images. The performance of these systems, as evaluated from in-orbit engineering data, are discussed with particular emphasis on the geometrical characteristics.

I describe two critical subsystems of the UCLA Reticonm Spectrometer: the pulsed-reset charge-sensitive preamplifiers and the duty cycle invariant, temporally nonaligned clock drivers. I outline the evolution of the underlying design philosophies and present schematics and performance results.

A new photon sensitive camera has been developed that determines the position of each photon as it arrives. It is made from easily available parts, is reasonably compact, and modest in cost. The present version will supply 8-bit by 8-bit photon positions (256 x 256 pixels) at rates as high as 106/sec. It has a flexible two-dimensional format, allowing it to be used as a 256 x 256 pixel camera, a 64 x 1024 pixel camera, or any other format that keeps the total number of pixels constant, provided a linear resolution of about 10 microns is not exceeded. The present system records the sequence of photon positions digitally onto video tape using a portable VHS format video tape recorder. Two hours of data can be recorded on a single cassette tape. Although this recording scheme limits the camera to rates of only 105 detected photons/sec, it is still faster than direct digital recording onto portable computer tape drives. If there is no need to store the positions of the individual photons, and the photons are directly summed to form a picture, as in a computer memory, the camera can operate at its maximum rate. A microcomputer is used to monitor the performance of the camera by sampling the data at rates it can handle. The quantum efficiency of photon detection is that obtained with the usual photocathodes, namely about 10 to 20% at visible wavelengths. Since the camera counts photons it has a large dynamic range, and when the photocathode dark count is reduced by cooling, the noise in each pixel is that due to counting statistics alone even when the total count is small. The present application is directed towards speckle imaging of astronomical sources, high-resolution spectroscopy of faint galaxies in a crossed-dispersion spectrograph, and narrow-band direct imaging of galaxies, but other uses are clearly possible.

A compact, lightweight, photon-counting device with spatial capabilities will be described. Briefly, a photoelectron liberated at the photocathode is relayed, by a proximity focussed lens, to a triple microchannel plate intensifier, of which the first plate is filmed to protect the photocathode from damage by ion feedback. The resultant electron cascade is incident on one of a variety of possible position sensitive encoders. The position of arrival of the original photon is equated with the centroid of this charge cloud. Results obtained with present devices will be presented and major factors which limit the performance of such detectors, in terms of spatial resolution, count rate and lifetime, will be examined. This leads to the prediction of the ultimate limits achievable with practical devices of this nature.

A photon counting system has been developed as a common-user instrument for spectroscopy at SAAO (South Africa). A dual Reticon array with EMI and Varo intensifiers is used. The system is based on modular design using CAMAC. Frame subtraction and event centring to half a diode are incorporated. The hardware of the system, including the detector head, is described and details of setting up problems are discussed. Astronomical performance is summarised and some general performance tests are presented. Count rates up to 5 counts per pixel per second are achieved with negligible dark noise. Typical resolution is 25 microns (FWHM) over 20 mm.

The slow-scan television camera being built for NASA's Galileo Jupiter orbiter spacecraft consists of a 1500-mm-focal-length telescope coupled to a camera head housing a newly developed 800 x 800 element charge-coupled device (CCD) detector based on "virtual phase" charge transfer technology. This detector results in a broad-band sensitivity over 100 times that of a comparable vidicon-tube camera while also yielding improved resolution, linearity, geometric fidelity, and spectral range. In the near-Jovian radiation belts, interactions of high-energy particles with the silicon CCD result in the production of unwanted charge, and special techniques have been implemented (e.g., tantalum and quartz shielding, rapid image readout, and 2 x 2 picture element on-chip averaging) to ensure adequate signal-to-noise performance for images acquired as close to Jupiter as five planetary radii. The images returned from Galileo will provide high-resolution (approximately 1 km) mapping coverage of most of the surface of the four large Galilean satellites of Jupiter with coverage of selected targets at resolutions as good as about 20 m. The broad spectral range of the instrument (0.4 to 1.1 pm) and use of special methane-absorption-band filters in the near-infrared will allow study of the Jovian atmospheric structure and dynamics. Excellent off-axis light rejection and high sensitivity of the instrument will permit study of low-light-level phenomena such as lightning and aurorae on Jupiter, and the Jovian ring.

The Wide Field and Planetary Camera instrument is being constructed at JPL as one of the instruments on Space Telescope. The instrument will be used to map the Universe and to study the outer planets. It will be able to see deeper into the heavens (by a factor of 1000) than has ever been seen before. The predicted performance will be reviewed along with a description of the instrument, and its current fabrication status.

A design approach for a camera to be used with the space telescope is given. Camera optics relay the system pupil onto an annular Gaussian ring apodizing mask to control scattered light. One and two dimensional models of ripple on the primary mirror were calculated. Scattered light calculations using ripple amplitudes between x/20 and x/200 with spatial correlations of the ripple across the primary mirror between 0.2 and 2.0 centimeters indicate that the detection of an object 109 times fainter than a bright source in the field is possible. Detection of a Jovian type planet in orbit about a Centauri with a camera on the space telescope may be possible.

Since two years a wide field prime focus camera is operating via remote control at the ESO 3.6m telescope. A description of this automatic plate and filter changer and the first tests of an automatic guider will be presented. The general plans for remote control of ESO instrumentation, including control from Europe, will be discussed.

Electrography is, in many respects, a nearly ideal electronic imaging technique. However, at very low light levels, although individual photoelectron events are in principle detectable in the film images, limitations are imposed by microphotometer and emulsion grain noise. The use of microchannel intensification allows individual photoelectron events to be unambiguously detectable and measurable, with little loss in achievable resolution. This significantly enhances the capabilities of electrographic detectors for use in imagery and spectrography of faint, diffuse objects or in applications which require a fast time response. We have conducted a quantitative study of the gains in detectivity and signal-to-noise ratio provided by this technique, through microphotometry and computer analysis of images of identical or similar laboratory light sources, using both unintensified and microchannel-intensified electrographic Schmidt cameras. We describe applications of the technique to far-ultraviolet wide-field-imaging and nebular spectrograph experiments, both of which have been used in sounding rocket flights and are planned for near-future Shuttle missions.

A review of the properties of classical image slicers is given and the description of a modification of the Bowen-Walraven device follows. This description includes light path, discussion of fabridation errors and assembly and testing of prototypes produced at Kitt Peak National Observatory. Considerations about further development of image slicers conclude the article.

A four channel photometer is in the final stages of construction at Steward Observatory. The instrument will obtain redshift estimates for distant (z,l) elliptical galaxies to at least 10% accuracy in short (15-20 minutes) integrations on the Multiple Mirror Telescope (MMT). Redshifts will be determined from comparison of visual and near infrared colors with those expected from a redshifted standard elliptical galaxy spectrum. The four channels are 0.4-0.7 microns (V_B), 0.7-0.95 microns (R_B), 1.4-1.8 microns (H), and 1.9-2.5 microns (K). Three dichroic filters allow these to be measured simultaneously. A silicon photodiode is used for R_B,indium antimonide diodes for H and K, and a photomultiplier for V_B. The diodes are all operated at liquid helium temperature to reduce thermal background and preamp noise, while the photomultiplier operates at room temperature using magnetic defocusing. Under these conditions the photometer will have sky background limited performance on the MMT, even in dark time, in all four detectors. Details of the instrument design are presented.

A solar corona photoelectric photometer has been constructed that operates at the three coronal lines, Fe XIV (5302.9 Å), Ca XV (5694.5 Å) and Fe X (6374.5 Å), using mica etalons and narrow-band interference filters. The photometer is used with a 40-cm coronagraph feed. In each case, the corona is discriminated from the sky background, by means of polarization-chopping between the line passband and a reference continuum passband. A mica etalon allows the reference passband to be arbitrarily located in the vicinity of the spectral line. Also, the width of the etalon passbands can be matched to that of the coronal line width, and the transmittance can be high if extremely transparent mica is used. A photomultiplier detects the two signals, their difference being proportional to coronal radiance. The photometer performance is illustrated by radiance plots derived from observations obtained at a fixed height in the corona at equally-incremented field points around the limb.

The idea of a photoelectric technique applied to differential astrometry has been around for about a decade. When developed such instruments promise increased accuracy and speed. Using linear detectors they can determine relative magnitudes and colors of all stars in the field at the same time that the relative positions are measured. Three such instruments have been proposed and have been developed to various degrees. These instruments and several variants will be reviewed. The current status of one instrument employing a rotating Ronchi linear grid, called the AMAS, will be discussed in detail. An accuracy of 5 μm in position is achieved routinely and proposed improvements project an improvement of a factor of ten to 0.5 μm. At this point the accuracy will be "seeing" limited and further improvement will be at the expense of observing time. The present instrument is sky limited at a magnitude of 11.5(V). A very minor change will increase this limit to 15.5(V) using two minute integration periods.

We have investigated three aspects of the performance of the MkII Camera for stellar photometry: (1) intrinsic errors from plate to plate; (2) variations in sensitivity across the field; and (3) the extent of color transformations required and their stability with time. All evaluations were performed using plate material obtained at the telescope. Although the detector in this case was an electrographic camera, the techniques described can be used with any panoramic detector system. Briefly, the general conclusions from this evaluation are: Relative magnitudes and colors can be determined to an accuracy of 0.02 magnitude over a 2-magnitude range in the non-sky-limited case. Only simple aperture integration algorithms need be used, and flat-field and geometric distortion corrections are not necessary to obtain reliable results with the camera. Color transformations are on the order of 0.1 mag/mag, and are quite stable in time and reproducible from cathode to cathode.

A new automated astronomical image classifier is described. The classifier is of the Bayesian type using maximum-likelihood template fitting with Poisson noise. The method's advantages are that there is no need for an explicit galaxy model, it provides a continuous spectnirn between totally unresolved objects and obviously diffuse resolved galaxies, and it can assign a probability to the classification. The continuous nature of the classifier allows identification of intermediate types such as stellar objects with faint nebulosity and galaxies with bright unresolved nuclei. The ability to assign a probability to each classification allows a determination of when the noise, plate quality, and scale of the images no longer gives a sensible division of stars and galaxies. Also the probability allows the weighting of objects in statistical studies relying on this separation. The method is applied to the catalog of 4-meter prime focus plates automatically reduced by the FO CA S system. It is compared with the hypersurface clustering classifier of Jarvis and Tyson.

In order to understand better the image description parameters generated by the FOCAS (Faint Object Classification and Analysis System) automatic astronomical image cataloging system, we have synthesized and analyzed images of dim galaxies. These simulated galaxy images were created from brighter galaxy images by geometric size reduction and intensity scaling followed by a convolution with a stellar image. The synthesized images are added at random locations to existing, digital images and the modified images are processed. The simulated galaxies are distinguished from the intrinsic images in the field by matching positions. The image parameters thus obtained serve to increase confidence in the automatic cataloging and calibrate various data reduction procedures.

In recent years, the demand for improved management of Earth resources has increased. At the same time, the proven ability of Earth-orbiting satellites to obtain accurate and timely information for this management has been demonstrated several times. Return Beam Vidicons (RBV) and Multispectral Scanners (MSS) are orbiting now, the Thematic Mapper (TM) is slated for a near-term Shuttle launch, and advanced definition is being done to determine technology capability of the next generation Earth resources satellites. This conceptual system will likely utilize "pushbroom" (linear arrays normal to orbital track using the orbital velocity to provide a 2-dimensional map) techniques with one linear array for each of the spectral bands required for information gathering. This discussion takes user requirements, as determined by NASA, and considers the possibility of using a preliminary system derived for those requirements to gather similar information on other planets. Relative levels of solar irradiance, planetary characteristics, and other solar system information have been used to find possible orbits, comparative signal-to-noise, ranges of sun-synchronous orbits, and other information regarding possible operation of this Earth-oriented system for other planets.

The Diffuse Infrared Background Experiment is a 10 band filter photometer that will operate at liquid helium temperatures. Diffuse galactic and extragalactic infrared radiation in the 1-300 micron wavelength range will be measured by the instrument. Polarization measurements for the 1 to 3.5 micron range will also be made. In this paper we present the conceptual optical design of the instrument.

A wide field photon counting array system proposed for the STARLAB space telescope detector system is described. Based on an Australian prototype, the Large Format Photon Counting Array offers 90 mm format, 12.5 micron resolution over a wide UV-optical wave-length region together with spatial stability and coherence at the 2 micron level.

Field correctors for a one-meter, f/15 cassegrainian telescope were designed as part of a NASA-funded study of an astronomical observatory on board of the space shuttle. By means of a Gasgoigne corrector and a biconcave field flattener, astigmatism and field curvature are corrected in a 0.6° field. Applicable wavelength ranges are limited by chromatic aberrations. The upper wavelength is selected to match a photocathode response limit. The lower wavelength limit is defined by a filter. Examples of usable wavelength ranges are: 210 nm - 1100 nm (multialkali photocathode, fused-silica corrector elements), 177 nm -320 nm (cesium telluride photocathode, calcium fluoride correctors); and possibly 134 nm -133 nm (cesium iodide photocathode, lithium fluoride correctors). Residual rms lateral color is smaller than 0.02 arc sec, and axial color is smaller than 0.25 arc sec (blur diameter at the ends of the wavelength range). The correctors introduce a small amount of coma. This is compensated by adjustment of the conic constants of the telescope mirrors.

The electronic control of astronomical instruments has become a very complex subject in recent years. The difficulty in dealing with these systems has, however, been significantly reduced through the use of microcomputers. The recent upsurge of commercially available microcomputer circuit boards and related peripheral devices has provided a convenient and cost effective base from which to develop space-borne astronomical instrument control systems. The use of a high level language (FORTH) for flight computer software development has further reduced costs to a minimal level. We report on the development of a flight computer system for the Ultraviolet Imaging Telescope (UIT) utilizing such an approach. Most of the breadboard version of the flight computer is assembled from commercially avail-able components, reducing the necessary circuit design to a few specialized interface and control cards. It is therefore possible to begin software development in parallel with flight hardware development, resulting in considerable time savings over traditional methods. The commercial boards are then re-fabricated on aluminum core heat conducting stock, using high reliability parts to produce the flight versions. The UIT Instrument Ground Support Equipment (IGSE) is comprised of a MINC-23 minicomputer. This system performs multiple functions such as flight computer software development, PROM programming, test and integration support, and flight operations support. We describe the implementation of these functions as they apply to the flight computer and telescope control concepts.

Through the years, astronomers have accumulated units and nomenclature that they understand and promulgate, but that are not understood by most engineers and some physicists. For example, astrowmers,use the term Jansky in place of the former "flux unit," which they define ag 10^-26 W/m₂ Hz. The,steps in converting to spectral areance [flux density] in watts/cm² μm or watts/cm² cm_-1 are described later. Other terms, which engineers should know, and their units are given in the Nomenclature.