The scientific objectives of multi-object fiber instruments on 8 m class telescopes may significantly depart from those carried out on 4 m class telescopes. Crude anticipation of future programs on these instruments allows to predict that targets will be mainly point sources or of low extension, with magnitudes up to approximately 22. With these characteristics, some observational aspects are investigated: (1) The (blind) positioning error budget constrains the astrometry to within 0.2' rms to keep photon losses at an acceptable level; (2) All-sky atlases from Schmidt plate scans, when available, will provide the relevant information for most programs; (3) Cross- identification or special observing procedures may be required for guide stars if they have a different origin than targets; (4) Atmospheric effects are investigated. Chromatic dispersion is shown impossible to calibrate out. The observation wavelength must be properly related to the acquisition and guiding wavelengths, constraining the use of filters; (5) Other observational constraints like sky subtraction or high spectral stability can lead to specific observational procedures. General observing modes are briefly reviewed. The impacts on the performances, described in terms of `Realizable Multiplex Advantage' (RMA) is described. At best, the RMA can reach one third of the number of fibers.

We describe the conversion of an existing f/8 Cassegrain spectrograph to a floor-mounted spectrograph fed by 94 fibers from the f/5 prime focus of the Shane 3-meter telescope at Lick Observatory. The spectrography forms part of the automated Multi- Object Spectrograph system developed as a collaboration between UCO/Lick Observatory and the Lawrence Livermore National Laboratory. Fibers from a robotic fiber-positioner at prime focus degrade the f/5.5 beam from the telescope (after it has passed through a wide-field prime focus corrector) into roughly a f/4.5 beam. If the 4/8 spectrograph were fed directly with this f/4.5 beam approximately 68% of the light would be lost. A simple optical system has been designed that converts the light from the fibers into the f/ratio expected by the spectrograph. The conversion optics are mounted at the entrance to the spectrograph. We describe focal ratio degradation tests of a variety of optical fibers and the design of the `pseudoslit' which mounts the fibers in a line at the input to the conversion optics.

Fiber-fed spectrographs have now been employed in astronomy for several years. They offer the principle advantages of increasing the number of objects with which simultaneous spectra may be recorded, better stability, an improvement in versatility, and factors associated with the mode-scrambling properties of fibers. However, the nature of these spectrographs pose new questions of certain design parameters. A traditional figure of merit for spectrographs is the throughput-resolution product (A(Omega) R). It is shown that A(Omega) R is no longer a constant as the entrance `slit' is varied. Here, `slit' has a new meaning. In both the first and higher order optics sense, A(Omega) R is investigated and compared with a better figure of merit. This new figure of merit maximizes the potential information content at the spectrograph focal plane. At a minimum, it incorporates the oft neglected instrument response and transmission/efficiency parameters (such as with a grating). Other refinements are made as well. Comparisons may be made both across spectrometer types and as a design guide within a family, where options must be evaluated.

The prime focus of the William Herschel telescope provides a wide field (one degree) for fiber spectroscopy. The production of the fiber feeds, which run from the prime focus to one of the Nasymyth platforms, has required the development of a multiple fiber to fiber connector together with techniques for mounting micro-lenses at the input to the spectrography. The protection of the fibers on the telescope, coupled with careful routing, has led to good focal ratio degradation (FRD) performance. A system for measuring the variation in transmission of the fibers on the telescope has been produced; the technique allows these measurements to be made under normal daytime lighting conditions.

WYFFOS is a spectrograph, currently being assembled, for multi- object spectroscopy using fiber-optic inputs. Initially 126 fibers, later 150 finer fibers (described in a separate paper) will enter it from the prime focus of the 4.2-meter William Herschel Telescope. WYFFOS uses the Baranne white-pupil, Littrow- mount optical system, given a wide 2D filed of view at the grating, high efficiency and a wide range of spectral resolutions. It has a twice-through lenticular collimator and a Schmidt-type cryogenic camera, operating from 350 nm to one micron. We shall install the spectrograph on an optical bench on one of the Nasmyth platforms of the telescope. One advantage of using the optical bench is that the spectrograph's components can be re-arranged, converting the reflection-grating instrument to a transmission-grating instrument. Possible future enhancements include increasing the number of fibers to 300 in the transmission grating mode, and adding a dioptric camera.

The 1.2-m United Kingdom Schmidt Telescope has operated a wide- field spectroscopy service for a number of years. A new common- user system has recently been completed. The instrument, known as FLAIR II, offers many more fiber channels than its predecessors, together with wider spectral coverage and faster turn-round of target fields. This paper describes FLAIR II in its present-day form, highlighting the most innovative aspects of its design, and giving a critical evaluation of its performance. Its impact has been significant, and large data-sets are being accumulated for a variety of object-classes.

The Anglo-Australian Telescope has just received a new prime- focus corrector, designed by Damien Jones (Prime Optics, Qld., Australia) and manufactured by Contraves, USA. The corrector is capable of producing aberration-corrected images over a full 2 degree diameter field of view. It is a 4-element design, the first two elements being rotatable cemented prismatic doublets approaching 1.0 m in diameter, which permit full atmospheric dispersion compensation to high zenith distances. The corrector is at the heart of a new powerful 400-fiber spectroscopic survey facility known as the 2dF. This A$2.3M project represents the largest investment in new technology and instrumentation the AAT has seen in its 20 year lifetime and will provide the telescope with a new and important role for large-scale statistical studies in the latter half of the decade and beyond. This paper will present the performance specifications for the corrector comparing them to the results of the recently complete telescope commissioning test.

In this communication we describe two optical fiber systems contrived to perform simultaneous bidimensional spectroscopy of extended objects: 2D_FIS and HEXAFLEX II. The main component of 2D_FIS is an optical fiber bundle which links the auxiliary Cassegrain focus of the 4.2 m William Herschel Telescope (WHT) with the ISIS spectrograph. HEXAFLEX II has been designed for the Cassegrain focus of the 2.5 m Nordic Optical Telescope (NOT) and it uses the FLEX spectrograph. Both telescopes are at the Observatorio del Roque de los Muchachos, on the island of La Palma. The basic component, the fiber bundle, is similar in both systems although each one is adapted to the particular characteristics of the corresponding spectrograph and telescope. Each one of the bundles is composed of 125 fibers: 95 to observe the object and 30 to obtain the sky background signal. Details of the acquisition procedures are provided. These systems have been tested at the telescope with success. Some examples of results on astronomical objects are shown.

The KPNO fiber-fed, multi-object spectroscopic instrument, Hydra, is being moved from the Mayall to the WIYN telescope. The WIYN telescope has good concentricity between the focal surface radius and the exit pupil. The primary modification to the instrument will allow the fibers to align with the telescope exit pupil while lying along the curved focal surface. Maximum pupil alignment losses will be reduced from 15% at the Mayall to 5% at the WIYN. The new orientation of the instrument requires a different mechanism for accessing the fiber and focal plate for maintenance. We are also upgrading the manner in which the fibers are held in place around the focal plane in order to reduce neighboring fiber interactions beyond the pivot circle. The wavelength calibration assembly is being modified to take advantage of extra room in the instrument. For guiding, instead of using offset guide probes, we are developing an algorithm which will utilize the field orientation probes. The Bench Spectrograph associated with Hydra is also being moved over to the WIYN, however, we do not discuss the spectrograph in this paper.

Sky subtraction with fibres is known to be more difficult than with slits. The scientific objectives relevant to carry out with multifibre instruments, even in the new age of 8-10 m telescopes, mainly deal with objects of magnitude <EQ 22. The requirement in beam switching methods to reach the ultimate performances is controversial. In this paper, we present the results of sky subtraction tests that have been performed on the 3.6 m ESO telescope. The two basic points we wanted to address were the ability of fibres to allow sky subtraction up to the 22nd magnitude, and whether or not beam switching is required. We detail the data reduction steps we have employed. We define all the possible techniques that can be used for sky subtraction and give the corresponding expressions for spectrum extraction. Last, we present the results we have obtained, and conclude that sky subtraction with fibres is quite feasible, even on 4 m telescopes, up to b(subscript $japproximately equals 22 without resorting to beam switching techniques.

A 640 fiber feed for a pair of moderate resolution spectrographs is being constructed for the sloan digital sky survey. The spectrograph slits, optical fibers and plug-plates are mounted together in removable cartridges. The cartridges protect the optical fibers and provide quick-change interfaces to the telescope and the spectrographs. Ten cartridges will be made to allow plugging to occur during the day. The fibers are constructed in harnesses of 20. These are mass-terminated in v- groove blocks at the spectrograph slit. At the input end the fibers are terminated in simple ferrules and manually plugged into aluminum plug-plates. The plug-plates are deformed to match the best focal surface of the telescope, and the holes are drilled to be parallel to the principal ray after bending. We describe a simple technique for drilling accurate holes.

'FUEGOS' (Fibre Unit for European General Optical Spectroscopy) is one of the foreseen focal instruments for the future ESO VLT (very large telescope). The goal is to provide the european community with first class equipment allowing high and low resolution spectroscopy for stellar and extragalactic observations in a large field. This large field of view, 30 arcmin provided by the VLT, is quite unique on 8 m class telescopes. The instrument is made of two parts: a fibre positioner attached to the Nasmyth rotator and a spectrograph sitting on the Nasmyth platform. The two assemblies are linked together with optical fibres. The instrument will include two different modes: the MEDUSA mode for the multi-object spectroscopy and the ARGUS mode for the 2D spectroscopy for extended objects. The multi-object positioner is of the robot type, based on a design using two gripper heads travelling simultaneously on a X-Y carriage. It locks magnetically 80 independent optical fibre bundles at object coordinates on a metallic focal surface. 2D spectroscopy is provided through a fibre anamorphoser in three different fields and spatial samplings. The spectrograph is of the 'white pupil' type, based on a catadioptric design with spherical optics throughout. It gives access to spectral resolutions ranging from 1500 to 30000. The detector is a 2048 x 2048 CCD located inside the camera optics.

We are currently testing an automated fibre positioner for the 4.2 m William Herschel Telescope (WHT). This instrument, known as Autofib-2, operates at the prime focus where it is able to utilize the full 1 degree field provided by the prime focus corrector (PFC). The robotic positioner is able to place 160 optical fibres in the focal plane of the WHT which feeds the light to a dedicated spectrograph (WYFFOS) located on the Nasmyth platform. This paper contains a description of the instrument which highlights the new techniques demanded by the prime focus plate scale and the scale distortions due to the PFC and its atmospheric dispersion compensator. These include robot vision to help achieve the high positioning accuracy and the use of two sky viewing probes to accurately determine the time dependent transformation from celestial coordinates to instrumental Cartesian coordinates. Also presented are the initial technical results on the performance of the instrument and the operational results of particular interest to the astronomical observer.

In this paper we describe the impact that instrument design can have on the overall performance of the Gemini Telescopes. We discuss the interaction between the instruments and some of the other telescope facilities such as A&G and Adaptive Optics. We also briefly describe the instruments that have been proposed for delivery during the construction phase of the project and list some of their features.

The instrumentation plans for the 8 m Japan National Large Telescope (approximately equals SUBARU) are reviewed. The topics described in this article are (1) the interface conditions between the telescope and the observational instruments at each focus, (2) Cassegrain auxiliary optics layout as an example to show the focal area layout, (3) scopes for optical and infrared detectors, (4) the outline of proposals for observational instruments, (5) the domains in the manifold of observational parameters covered by these instruments, and (6) the schedule of construction of instruments.

This article describes the design and construction of a CCD camera for the f/9 Cassegrain focus of the 200-inch (5m) Hale Telescope at Palomar Observatory. This instrument utilizes a set of 18-inch (0.45m) diameter lenses to change the Cassegrain focal ratio from f/16 to f/9, and the optical design prescription of these lenses is reported. For CCDs having 24 micrometers pixels, the f/9 focus gives a reciprocal plate scale of 9 pixels per arcsecond, which is well suited to precision photometry as well as future application to adaptive optics. In addition to the CCD and shutter, the instrument also incorporates an offset guider and an 8-position filter wheel.

The stellar coronograph built by STScl and the OATO operating at the SUSI focus of ESO's New Technology Telescope (NTT), described with particular emphasis on its optical and mechanical characteristics, is one of the most powerful coronographs in operation. Observations with angular resolutions of 0.6 arcsec over field of view of 45 arcsec diameter have been routinely achieved in the observing runs carried out so far. We describe the results from the application of the coronograph to the problem of observing the inner regions in the (beta) Pictoris dust disk.

The Low Resolution Imaging Spectrometer is designed for use at the Cassegrain focus of the Keck 10-m telescope. It provides the capability of acquiring low resolution (R equals 1000 to 5000) digital spectra, as well as 6 X 8 arc-minute moderately high spatial resolution (4.65 pixels/arc-second) direct images. Spectroscopy can be carried out with single slits which are 3 arc-minutes long. In addition punched multi-slits can also be employed which allow for the acquisition of at least forty spectra simultaneously. Since the instrument is designed to be as efficient as possible, it is a double spectrograph, with a dichroic splitting the blue and red light into separate optical paths after the collimator. Only the red side has been constructed thus far. With a 2048 by 2048 thinned Tektronix CCD as the detector the total efficiency of the red side at the peak of the grating blaze is predicted to be nearly 40%. Results of the commissioning observing runs will be described.

An infrared camera has been successfully coupled to the Fourier Transform Spectrometer (FTS) at the Canada-France-Hawaii Telescope (CFHT), making a unique infrared spectrometer. This instrument, the only one of its kind in the world, is capable of simultaneously acquiring both images and spectra of astronomical sources in the 1.0 to 2.5 micrometers wavelength range across its 24' field of view. Successful observations have been made of various targets, including planets and emission nebulae. A description of the instrument, data analysis, and scientific results, is presented below.

A specially designed faint object spectrograph in the near-IR region from 1 to 2 micrometers is proposed for the Japanese National Large Telescope: SUBARU. The proposed instrument called OHS for SUBARU is kind of a pre-optics system capable of eliminating most of intense OH airglow emission lines from the incident beam in the J- and H-passbands. The detectivity for objects in the faintest end is supposedly enhanced with this spectroscopic filter system by removing nearly 95% of the natural sky background: the non-thermal night airglow emission. The sensitivity gain in terms of limiting magnitude in these wavelength bands is expected to be 1 to 1.5 mag, depending on the modes of observations. The expected performance of the prototype OHS when attached to SUBARU will also be presented.

The requirements for medium/low resolution optical spectroscopy with the GEMINI telescopes are discussed. Two different modes have been identified to exploit the exceptional image quality expected from the telescope and its Adaptive Optics (AO) system while also providing a wide range of spectral resolution options over a larger field. Meeting these conflicting requirements within a single instrument poses a major challenge, and it may prove necessary to construct two devices.

The design and the expected performance of the FOcal Reducer/low- dispersion Spectrograph (FORS) for the Very Large Telescope (VLT) of the European Southern Observatory (ESO) are described. FORS is an all dioptric focal reducer designed for direct imaging, low- dispersion multi-object spectroscopy (MOS), imaging polarimetry and spectro-polarimetry of faint objects in the spectral range from 330 nm to 1.1 (mu) $m. The field of view is 6.83 X 6.83 arcmin² with an image scale of 0.2 arcsec/pixel. To take full advantage of excellent seeing, a configuration with an image scale of 0.1 arcsec/pixel can be selected. In the MOS mode, simultaneous spectroscopy of up to 19 objects is possible. Two copies of the instrument (denoted `FORS I' and `FORS II', respectively) are under construction and will be installed at the Cassegrain foci of the VLT unit telescope Nos. 1 and 3.

The MOF is a compact device (15 cm max dimension) displaying a very narrow-band spectral transmission (20 to 70 m$angstrom, single or multiple bands) with intrinsic absolute spectral reference and stability, high peak transmission (close to 50%) and imaging capability. It has been used so far mainly in solar astronomy to detect solar magnetic and velocity fields. Doppler shifts as low as 1 cm/sec equivalent velocity can be measured on the sun (whole disk) using 2 cm aperture telescope and 1 sec exposure time. Its working principle is based on magneto-optical effects on metallic vapors in a magnetic field. An overview of the theoretical model compared with experimental spectroscopic measurements is discussed in the first part. Applications in astronomy, namely helio and astero seismology and magnetographic observations are shown in the second part of this paper.

A multimode spectrograph for tridimensional spectroscopic observations of faint extended objects is under development. The spectrograph has four modes, i.e., the imager mode with narrow (or wide) band filters, the long-slit spectrograph mode for area spectroscopy by means of spacial scans, the Fabry-Perot interferometer imager mode, and the microlens-array (MLA) spectrograph mode. Selection of the mode is made by moving optical parts relevantly in the spectrograph. The principles of the optics of the first three modes are ordinary ones. In the imager mode, a field lens is inserted behind the telescope focus and filters are set between the collimator and the camera lenses, while a Fabry-Perot etalon is inserted instead of the filters in the Fabry-Perot imager mode. In the long-slit mode, a slit is set at the telescope focus, and a grism replaces the filters or the etalon. The principle of the MLA spectrograph mode is essentially same as that of TIGER for the Canada-France-Hawaii telescope. Our spectrograph, however, is equipped with a dual-channel preoptics system for the MLA, one channel acquiring a target object and the other the neibouring sky appreciabily apart from the target object. The image of the sky is projected on the microlenses along a side of the array of the microlenses. The spectra of the sky are used to eliminate of contamination by sky background from spectra of the target object. The design of this spectrograph is primarily optimized for the MLA spectrograph mode at the 1.88 m telescope at Okayama. With this telescope, about eighty spectra of an area about 9# x 15 of an object and fourteen spectra of the nearby sky are obtained with a spacial resolution of 1.3" which matches the average seeing size at the telescope site. Performances of this spectrograph when it is used for other telescopes, including the SUBARU, are also presented.

The VIMS-V is a passive remote sensing instrument under development for the Italian Space Agency to perform high resolution spectral imaging in the optical waveband. Its unique design relies substantially on conventional materials and fabrication techniques to obtain high sensitivity and versatility in a compact, lightweight, and low power instrument suitable for deep space missions. The prototype will fly on the Cassini spacecraft and operate in unison with the Jet Propulsion Laboratory's IR channel to map the surface spatial distribution of mineral and chemical species of Saturn, its rings, and its satellites.

A fundamental problem of adaptive optics systems is the very narrow corrected field-of-view (FOV) which can be obtained due to the fact that turbulence is extended in altitude throughout the atmosphere. The correctable FOV is on the order of 5 to 10 microradians in the visible. Previous concepts to broaden the corrected FOV have been hardware-oriented, requiring multiple wavefront sensors (WFS) and multiple deformable mirrors. In this paper we analyze the average performance of an image measurement and post processing technique which uses simultaneous measurements of a short exposure compensated image measured in an off-axis direction, and an additional WFS measurement taken in the off-axis direction. Results are presented for infinite altitude WFS beacons driving both the WFS for the adaptive optics and the WFS looking in the off-axis direction, a variety of seeing and WFS light level conditions, and off-axis angles from two to six times the isoplanatic angle. We find that this technique provides a significant boost in the average effective transfer function out to at least six times the isoplanatic angle.

The optical design of a general-purpose 1 to 5 micrometers cryogenic IR camera and spectrograph (IRCS) for the 8.2-m Subaru telescope is described. The camera section serves the essential purpose of a slit-viewer in order to permit efficient use of the spectrograph on faint objects. It will also serve as a multipurpose IR camera. The spectrograph section will have a resolving power of (lambda) /(Delta) (lambda) equals 660 to 1600. 1 to 2.5 micrometers or 3 to 5 micrometers will be observed in a single exposure by using gratings and cross-dispersing prism combinations. The slit length will be 3 to 5'. The camera section will have 3 pixel scales (0'.030, 0'.056, and 0'.125) that provide high spatial imaging, 1:1 imaging (high throughput), and `wide-field' (about 2' X 2'). The spectrograph section will have 2 pixel scales: 0'.05/pixel and 0'.125/pixel. The important features of the IRCS are: (1) Two pixel scales are available, one matched to the tip-tilt secondary and the other matched to the adaptive optics system. (2) Switching between imaging and spectroscopic modes is possible. Therefore observational programs can be optimized for the seeing, availability of guide stars, and weather conditions. (3) In some cases deep imaging can be undertaken while long exposures are made in the spectroscopic mode.

Following the availability on the market of IR arrays able to perform ground-based astronomical observations in the atmospheric windows longward of 2.5 micrometers , we started at the Torino Astronomical Observatory a new project aimed at the construction of a thermal IR camera to be installed at the TIRGO telescope. Located in the Swiss alps at 3100 m a.s.l., this Italian facility (1.5 m f/20 IR optimized) provides during the winter months a relatively high number of nights (20%) with first-rate conditions (low temperature and emissivity) for medium-IR observations. In order to fully exploit this potential, we designed an instrument, named Two-Channel Medium IR Camera (TC-MIRC) operating over the entire 1 to 14 micrometers region and optimized for the 2.5 to 14 micrometers thermal bands. TC-MIRC covers such a broad range of wavelengths using two IR array detectors: an InSb device for the 1 to 5 micrometers region and a Si:Ga device for the 8 to 14 micrometers band. The main characteristic of the camera is that both arrays can simultaneously observe the same region. In this way, we can not only approach an almost double observing efficiency (time really spent `on target'), but also use both detectors for correlated observations and testing of unconventional acquisition techniques. It follows that TC-MIRC is a complex instrument presenting several interesting features. Thanks to the presence of two independent optical channels, the user can change the filters, adjust the focus and vary the optical scale on a channel without affecting the acquisition running on the other array. In particular, the possibility of adjusting the optical scale on each detector during the observations allows the user to select the most convenient sampling and field of view on the basis of the actual seeing or diffraction conditions, background level and scientific needs. Moreover, the adopted cryogenic system is entirely based on a mechanical closed-cycle cooler and allows very low-cost operations and easy maintenance on the mountain for long periods of time. In this paper we present the opto/mechanical design and construction, the general structure of the control system and the software architecture. We report the performances reached by the most critical parts of the instrument during the test carried out in the laboratory and at the telescope during the first engineering run in January 1994.

This paper describes the performance of a unique new IR array camera system which provides simultaneous imaging at two wavelengths in the near IR. Two-color imaging is achieved with a dichroic beam splitter which yields two independent beams, one short-wave (SW) from 1 to 2.5 micrometers and one long-wave (LW) from 2 to 5 micrometers . A Rockwell NICMOS 3 256 by 256 HgCdTe array is used in the SW channel and the LW channel has an InSb 256 by 256 array from SBRC. The instrument, which is designed for the University of California's Lick Observatory 3-m telescope and for the f/15 focus of the 10-m W.M. Keck telescope, employs a closed cycle refrigerator and a compact array control/data acquisition system based on transputers with a host 486 PC. On the Lick 3-m telescope the pixel size is 0.7' which gives a field of view of about 180' by 180'. Facilities are also provided for spectroscopy and polarimetry. Recent observational results are reported to illustrate the performance of this system.

We present data on the image quality achieved with the near IR array spectrometer cooled grating spectrometer 4 (CGS4) on the UK IR telescope (UKIRT) on Mauna Kea. A design spot size of 30 micrometers was specified for CGS4, to maintain acceptable image quality with both the 58 by 62 pixel array with which it is currently equipped and the 256 by 256 array which CGS4 was also designed to accommodate. Details are given of the design, construction and alignment method which allow linear tolerances of 50 micrometers and angular tolerances of 25 mrad to be met and maintained at cryogenic temperatures. The instrumental flexure is also discussed. Both laboratory spectra and those taken at the telescope illustrate that design spot sizes of 30 micrometers have been achieved in the near IR. It will be demonstrated that the theoretical resolution of the instrument is attained for resolving powers from approximately 200 to 20,000.

We describe a slitless spectrograph designed for use in the IR region between 2.6 and 5.2 micrometers . The dispersing element is a grism fabricated in silicon by binary-optical techniques. This approach permits the incorporation of aberration correction into the grating element. When combined with simple, all-silicon field and camera optics, the grism forms zero-order images and 3.5 mm- long dispersed spectra on a 256 by 256 element array of 38 micrometers InSb detectors. Interchangeable field lenses provide for 8:1, 6:1, and 4:1 reduction to a final focal ratio of f/2.5.

We present a description of the mid-IR camera system (MIRCAM) currently under development at the University of California, Irvine. MIRCAM is a portable imaging system, specifically designed for diffraction-limited, broadband imaging in the 4.7 micrometers (M band), 10 micrometers (N band), and 20 micrometers (Q band) atmospheric windows. MIRCAM is designed for operation with the new generation of high-background 256 by 256 Si:As IBC arrays currently under development by both Rockwell International and Hughes Aircraft. However, initial operation will proceed with a 128 by 128 Si:As IBC array manufactured by Rockwell International. We have also designed a state-of-the-art control and data-acquisition system that is capable of reading out the 256 by 256 array at a rate of 500 frames per second, or 2000 frames per second for the 128 by 128 array. The fully-reflective optics are designed for Nyquist-sampling at the telescope diffraction limit, and exhibit spot sizes that are considerably smaller than the pixel size over the entire 256 by 256 array. Four interchangeable optical configurations permit use of MIRCAM on the Lick 1-m, IRTF 3-m, UKIRT 4-m, and Keck 10-m telescopes.

The MegaCam is a multi-purpose, wide-field, two-color camera being designed for use at the UH 2.2m telescope. The camera will utilize a Rockwell 1024 x 1024 HgCdTe detector array for 1-2.5 micrometers imaging, and a 2048 x 4096 frame-store CCD (2048 x 2048 active area) for optical imaging. The optics are based on a modified Offner relay design with additional lenses to give a 2:1 magnification in the infrared channel for a field of view of 5'.8 x 5'.8 (0.34 arcsec/pixel) using the f/10 telescope secondary, or a scale of 1'.9 x 1'.9 (0.15 arcsec/pixel) at f/31. This design provides a simple, high-throughput, and compact optical layout. A beamsplitter is placed in front of the IR optics at a low angle of incidence to form the optical image at 1:1 magnification on the CCD, for a field of view of 4'.7 x 4'.7 and 1'.5 x 1'.5 at f/10 and f/31, respectively. The optics and filters are to be housed in a LN₂-cooled dewar. The CCD and IR arrays will be operated with modified SDSU-design controllers. The user interface will have several modes to make simultaneous optical/IR imaging simple to configure and perform at the telescope.

We describe an IR multi-fibre system we are currently building for UKIRT. SMIRFS (Spectroscopic multiple infrared fibre system) will feed the CGS4 spectrograph, providing it with a multi-object capability in the J, H and K bands. For efficient coupling the inputs and outputs of the fibres are microlensed. Because the telescope is normally focused inside CGS4 for conventional spectroscopy the SMIRFS fibre slit is projected in to CGS4 by a spherical mirror. IR optimised Silica fibres are used for the J and H bands and Zirconium Fluoride fibres are used for the K band.

This paper describes the design of an IR cold coronagraph (CoCo) built by SETS Technology, Inc., for use at the NASA 3 m IR Telescope Facility (IRTF) at Mauna Kea Observatory, for the imaging of faint IR sources in proximity to bright sources. The coronagraph is designed to obtain high contrast photometric images by use of an occulting mask and a pupil mask. The coronagraph is to be used in combination with the IRTF NSFCAM, which covers 1-5 micrometers and uses a 256x256 InSb array. The platescale can be varied from 0.06'/pixel to 0.15'/pixel, covering a field of view of 14' and 38', respectively. Selectable apodized and hard occulting masks are mounted on a wheel as the first element in the system to reduce scattered light. Selectable pupil masks are cooled to 77K within the CoCo cryostat. The cryostat consists of a liquid nitrogen can for cooling the optics, masks, and baffles. The CoCo dewar is mounted on a slide in a housing to allow it to move out of the beam path so that the NSFCAM may be used with or without the coronagraph during the same observing period.

The design of a multichannel occultation photometer built under NASA contract to SETS Technology, Inc., for the NASA 3-m IR telescope facility (IRTF) and the JPL Table Mountain telescope is described. This instrument acquires data in four selectable passbands (two 1 to 5 micrometers channels and two 10 to 20 micrometers channels), with very high sensitivity and approximately 100% duty cycle on-source during chopping. The optics are optimized for uniform response across an aperture of up to 20 arcseconds on the IRTF. The cryogenic system is a two-can cryostat with one liquid nitrogen can for cooling the radiation shields, optics, filters, and baffles, and a liquid helium can for cooling the IR detectors. The instrument operates two types of IR detector technologies. The 1 to 5 micrometers detectors are low-capacitance, single-element InSb detectors. The 10 micrometers detectors are blocked impurity band detectors. The instrument also has a 64 by 64 visible CCD array as an additional channel for guiding and visible photometry. A global positioning system unit is incorporated into the system for time and location stamping of occultation events. The instrument design and construction are discussed.

We constructed a near IR camera PICNIC equipped with the 2D array detector NICMOS-3 manufactured by Rockwell. Employing a four aspherical metal mirror system for reimaging optics, PICNIC is an IR imager distinguished with high throughput and small chromatic aberration. In addition to normal imaging mode, the camera has a prism spectroscopy mode and a polarimetry mode. A direct view prism, which can be optionally inserted in front of the camera, make it possible to obtain multiobject low resolution spectroscopy in the wavelength range from 1 to 2.5 micrometers at resolving power of approximately 50. Linear polarization can be measured with combination of the filters and/or the prism. We realized user-friendly operating environment as well as automated observation.

We have just recently commissioned a new 1.0-5.5 micrometers IR array camera for the NASA IR Telescope Facility based upon the Santa Barbara Research Center 256x256 InSb array. The primary features of this new instrument are three user-selected platescales, a variety fo fixed bandpass filters, 1 to 2% spectral resolution circular variable filters, coronagraph masks, polarization imaging capability, an optical guider/imager, and a grism. In this paper we briefly outline the design and performance of the camera system, describe some unique operating modes, and show some recent images.

The present state of the art in scientific InSb focal plane arrays is defined by the Santa Barbara Research Center (SBRC) 256x256 device. In this paper we will discuss the status of the USNO-NOAO 1024x1024 focal plane development effort at SBRC. The project is in its ealy phases, and so this report consists of the device description, design goals, testing plans, and schedule. Drivers for even larger IR arrays include plans for large (8 meter class) telescopes, high resolution spectroscopy, astrometry of large fields, and wide field imaging amongst others. Focal planes of 640x480 have already been demonstrated, and so the step up to 124x1024 seems reasonable at this time.

We report on the development, fabrication and performance of a new class of thermal sensors for far IR and millimeter wave detection. These devices consist of small single crystal samples of ultra-pure, natural or isotopically engineered germanium which have been doped by the neutron transmutation doping (NTD) technique. The concentrations of the acceptor and donor dopants (N_A,N_D) can be accurately controlled with this technique. They depend on the thermal neutron fluence, the neutron absorption cross sections and the atomic fractions of ⁷⁰Ge (for the Ga acceptors) and ⁷⁴Ge (for the As donors), respectively. The values of N_A and N_D and their ratio result in a predictable resistivity of the Ge crystals down to temperatures of a few milliKelvin. The excellent control of the resistivity down to very low temperatrues, together with the development of ohmic contacts working at the lowest temperatures, allows the fabrication of high sensitivity bolometer arrays with over 100 pixels and highly uniform response.

We describe the design and manufacture of SCUBA, which is undergoing laboratory testing prior to commissioning on the James Clerk Maxwell Telescope on Mauna Kea, Hawaii. It contains two arrays, one of 91 pixels optimised for 450 micrometers and the second of 37 pixels optimised for 850 micrometers in close-packed arrays, with each pixel having diffraction-limited angular resolution. Some of the original design features of the instrument are described: the cryogenic system operating at 100mK; the optical layout; bolometer manufacture; and array integration. We illustrate the performance of the instrument with test results obtained during the laboratory commissioning.

Over the past 6 years the instrumentation team at the NASA IR Telescope Facility (IRTF) has designed and built 3 major facility instruments, two cameras and a spectrometer, for use by the IR astronomical community. We will report on many new techniques for cryostat construction that have been developed that deviate from traditional practices. These include aluminum electron beam welded vacuum and cryogenic enclosures, rectangular cryostat formats, use of closed cycle coolers and their performance, use of all aluminum structures, optimization of cryogenic performance without super insulation, activated charcoal getters, and optomechanical mounting. Cryostat performance data and methods for estimating cryostat performance will also be included.

The University of Hawaii and the Rockwell International Science Center are developing a large format SWIR detector array optimized for low background astronomical imaging and spectroscopic observations. This so called HgCdTe astronomical wide area IR imager (HAWAII) device will be based on the technology developed for the NICMOS project, but will incorporate several modifications of this design to improve the performance.

The signal to noise ratio of very faint object spectroscopy is discussed in the context of the gain in limiting magnitude attainable on very large telescopes at low spectral resolution. It is shown that if the multiplicative errors resulting from the sky subtraction are not corrected, deeper spectroscopy will not be obtained by increasing the telescope size. A new CCD observing technique, which we call `Va et Vient' spectroscopy, is described in detail. This is a beam switching method where the elementary exposures are short enough to freeze the sky temporal fluctuations, and where the CCD is read only after a series of a few dozen of exposures. During the integration, the signals from the object field and the reference sky are separated by shifting the charges onto the CCD along the columns. Analytical evaluations are confirmed by laboratory tests and show that this technique is photon noise limited even at high flux and thus can lead to deeper spectroscopy. We give estimates of the results that can be achieved with the new generation of very large telescopes.

The enhancement of the quantum efficiency of charge-coupled devices (CCDs) can be accomplished by several methods. The most dramatic increase comes from thinning the CCD for use in the back illuminated mode. Techniques to improve the QE of back illuminated CCDs include the deposition of backside thin film coatings to reduce reflection losses, surface charging to eliminate the backside potential well, and several aspects of device packaging. We have developed processes in these areas which have led to the post-manufacture optimization of devices for astronomical observations. WE describe our backside oxidation results and the interaction of the oxide with backside charging, the effect of ion absorption on backside charging, the development of one and two-layer antireflection coatings, and a new packaging method to improve near-infrared quantum efficiency.

While large area scientific CCD imagers have high resolution and sensitivity in the visible region, the UV and near IR wavelength regions typically have a decreased response. Therefore, modified designs and advanced techniques are used to broaden the range for high quantum efficiency. For the UV band, deposition of a very thin polysilicon gate allows transmittance of shorter wavelength photons, and frontside coating a completed device with lumogen absorbs lower wavelength photons and re-emits them near the peak sensitivity of the CCD. For the near IR band, high-resisitivity, thick epitaxial material is used for collection of longer wavelength photons. Overall broad spectral band QE is enhanced with backside thinning and antireflective coatings of various dielectric layers. QE has been predicted by calculating the transmission, reflection, and absorption over a cross section of the CCD. Data is presented to confirm the QE increase from 120 to 1000 nm. Design and fabrication are discussed for each improvement technique, as well as trade-offs in cost, device performance, and yield.

Results are presented on the fabrication and characterization of a 4Kx2K three-side buttable CCD produced by Orbit Semiconductor, a silicon foundry in San Jose, California. This first run of wafers was produced to test the ability of Orbit to produce high quality scientific CCDs with the characteristics required for detectors to be used in optical instruments of the Keck Observatory. Also on the wafer are two 2Kx2K devices. Similar devices have been fabricated for us by Loral/Fairchild. Extensive characterization of the Loral devices has taken place over the past few years, so interest is high about the possibility that Orbit might become a second source for similar detectors. This paper presents the first results on the 4Kx2K CCDs, and those preliminary results include measurements of charge transfer efficiency, low-temperature dark current, on-chip amplifier read- out noise, localized charge traps, full well, and responsive quantum efficiency.

We describe the design of an ultra-format, 8192 x 8192 pixel CCD mosaic imager under construction for the Mauna Kea Observatory. The mosaic will be built from a 4 x 2 array of 3-edge-buttable 2048 x 4096 15 micrometers pixel CCDs fabricated by Loral Fairchild. We outline the scientific justification for such a mosaic and the technical details of the 3-edge-buttable 2048 x 4096 CCD design. We also present our strategy for imager packaging and subsequent mosaic construction which will result in a mosaic with individual elements that can easily be installed and removed. This particular CCD mosaic is intended for two existing MKO telescopes: the UH 2.2 m and the CFHT 3.6m. In either configuration, the imager will offer an enormous field of view with excellent spatial sampling.

As astonomical CCD image sensors have incorporated more pixels the total readout time of the arrays has increased to the point where it can significatly reduce overall available observing time. The incorporation of multiple readout circuits on CCDs and multiple readout capability in their associated controllers allow several pixels to be read out simultaneously, reducing the overall readout time of the array. A controller is used to operate a single CCD containing four readout circuits that operate simultaneously, giving a factor of three reduction in readout time, and a small increase in readout noise. Another tactic for reducing readout time is described, that is easily implemented with programmable CCD controllers that reads out only selected regions of interest and discards the uninteresting portions of the image, giving a considerable decrease in readout time and no readout noise penalty.

University College London and The Imperial College of Science, Technology & Medicine are together developing a new large area imaging photon counting system, BIGMIC, for use primarily on very large telescopes. This detector is designed for applications requiring the highest sensitivity and resolution such as, high dispersion Echelle spectroscopy. The system incorporates a specially designed 75mm active diameter image intensifier fibre- optically coupled to a fast scanning 770 x 576 pixel frame transfer CCD. Photon events at the intensifier output screen are centroided to 1/8 of a CCD pixel in both X and Y in order to sample adequately the point spread function of the intensifier, giving a data acquisition format of 6160 x 4608 sub-pixles. The area imaged onto the CCD is 61mm x 46mm with a data acquisition pixel size of 10 micrometers . A hardware windowing facility, built into the detector system, enables the astronomer to select a subset of the imaging area for data acquisition. This permits the user to match the system to specific applications; for example in a number of spectroscopic applications an essentially one dimensional image is required and a detector format of perhaps 6160 x 100 pixels could be utilized.

CCDs are widely used in astronomy for spectroscopy, photometry, astrometry, and many other applications. This array sensor has a periodic structure which defines individual picture elements (pixels). The stability and excellent overall response of this type of detector are well known. Less widely described is the fact that the internal structure of the array gives rise to intrapixel variations in responsivity. These response modulations are particularly relevant when the data is spatially undersampled; a situation that is not entirely uncommon in certain instruments. We have made detailed measurements of the response variations within CCDs, using an experimental arrangement that gave a 2 micron resolution. Optical response has been determined at all sample points within a pixel, at selected wavelengths in the range 400 to 900 nm. Measurements are presented for front-illuminated thick (EEV) devices and backside- illuminated thin (Tek) CCDs. Models of the internal structure have been constructed and used to calculate theoretical response data; these have been compared with the experimental results. An example of an extracted (FOS) spectrum which demonstrates these undersampling effects is discussed.

We describe an image intensifier tube of flexible design, capable of being used for a number of different ground and space-based applications. The tube was originally designed to meet a requirement for an optical photon-counting detector sensitive between 150 and 650 nm with a spatial resolution of less than 20 micrometers . Other performance criteria aimed for were a peak quantum efficiency of greater than 20% and a 200 kHz maximum count rate. The tube has a 25 mm diameter image format which is nominally 2D, though 1D and non-Cartesian imaging formats could be accommodated. Photon detection is via a semitransparent photocathode coated on the detector input window. Liberated photoelectrons are proximity focused on to a microchannel plate (MCP) stack which provides electron gain with a saturated pulse height distribution for photon counting. Imaging is accomplished with conductive charge division readout. The detector geometry is easily modified to accommodate different types of this generic readout type. The imaging electronics consist of several parallel charge measurement channels, the number depending on the readout type. A decoding algorithm provides an x,y photon event coordinate. The detector was manufactured by DEP bv, Holland. The original design utilized an S20 photocathode on a magnesium fluoride or fused silica window but recently detectors have been made with calcium fluoride windows and caesium telluride photocathodes. All detector variants built thus far use a stack of three MCPs in a Z configuration producing an electron gain of between 10⁶ and 2 X 10⁷ depending on MCP conditioning. We present images and performance data from the two types of detector so far built; the original optical intensifier design with a SPAN six electrode image readout, and a variant with a UV photocathode and wedge and strip anode readout. We discuss the problems encountered during the tube development and the solutions arrived at for each type of device.