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The Dark Energy Survey Instrument (DESI) is a 5000-fibre optical multi object spectrograph for the 4m Mayall telecope at the Kitt Peak National Observatory. Ten identical three channel spectrographs will be equipped with 500-element fibre slits. Here we focus on the architecture of the science slits and the interchangeable auxiliary slits required for calibration.

The KPNO Nicholas U. Mayall 4-meter telescope is to be the host facility for the Dark Energy Spectroscopic Instrument (DESI). DESI will record broadband spectra simultaneously for 5000 objects distributed over a 3-degree diameter field of view; it will record the spectra of approximately 20 million galaxies and quasi-stellar objects during a five-year survey. This survey will improve the combined precision of measurement on the dark energy equation of state today (w 0 ) and its evolution with redshift (w a ) by approximately a factor of ten over existing spectroscopy baryon acoustic oscillation surveys (e.g., BOSS 1 ) in both co-moving volume surveyed and number of galaxies mapped. Installation of DESI on the telescope is a complex procedure, involving a complete replacement of the telescope top end, routing of massive fiber cables, and installation of banks of spectrographs in an environmentally-controlled lab area within the dome. Furthermore, assembly of the instrument and major subsystems must be carried out on-site given their size and complexity. A detailed installation plan is being developed early in the project in order to ensure that DESI and its subsystems are designed so they can be safely and efficiently installed, and to ensure that all telescope and facility modifications required to enable installation are identified and completed in time.

[The BigBOSS experiment is a redshift survey designed to map the large scale structure of the universe and probe the nature of dark energy. Using massively-multiplexed _ber spectroscopy over 14,000 deg2 of sky, the survey will deliver more than 20 million galaxy and quasar redshifts. The resulting three dimensional sky map will contain signatures from primordial baryon acoustic oscillations (BAO) that set a "standard ruler" distance scale. Using the BAO signature, BigBOSS will measure the cosmological distance scale to < 1% accuracy from 0.5

BigBOSS is a proposed ground-based dark energy experiment to study baryon acoustic oscillations (BAO) and the growth of structure with a 14,000 square degree galaxy and quasi-stellar object redshift survey. It consists of a 5,000- fiber-positioner focal plane feeding the spectrographs. The optical fibers are separated into ten 500 fiber slit heads at the entrance of ten identical spectrographs in a thermally insulated room. Each of the ten spectrographs has a spectral resolution (λ/Δλ) between 1500 and 4000 over a wavelength range from 360 - 980 nm. Each spectrograph uses two dichroic beam splitters to separate the spectrograph into three arms. It uses volume phase holographic (VPH) gratings for high efficiency and compactness. Each arm uses a 4096x4096 15 μm pixel charge coupled device (CCD) for the detector. We describe the requirements and current design of the BigBOSS spectrograph. Design trades (e.g. refractive versus reflective) and manufacturability are also discussed.

BigBOSS is a Stage IV dark energy experiment based on proven techniques to study baryon acoustic oscillations and the growth of large scale structure. The 2010 Astronomy and Astrophysics Decadal Survey labeled dark energy as a key area of exploration. BigBOSS is designed to perform a 14,000 square degree survey of 20 million galaxies and quasi-stellar objects. The project involves installation of a new instrument on the Mayall 4m telescope, operated by the National Optical Astronomy Observatory. The instrument includes a new optical widefield corrector, a 5,000 fiber actuator system, and a multi-object spectrometer. Systems engineering flowdown from data set requirements to instrument requirements are discussed, along with the trade considerations and a pre-conceptual baseline design of the widefield optical corrector, spectrometer and fiber positioner systems.

BigBOSS is a Stage IV Dark Energy instrument based on the Baryon Acoustic Oscillations (BAO) and Red Shift Distortions (RSD) techniques using spectroscopic data of 20 million ELG and LRG galaxies at 0.5≤z≤1.6 in addition to several hundred thousand QSOs at 0.5≤z≤3.5. When designing BigBOSS instrumentation, it is imperative to maximize throughput whilst maintaining a resolving power of between R=1500 and 4000 over a wavelength range of 360-980 nm. Volume phase Holographic (VPH) gratings have been identified as a key technology which will enable the efficiency requirement to be met, however it is important to be able to accurately predict their performance. In this paper we quantitatively compare different modelling techniques in order to assess the parameter space over which they are more capable of accurately predicting measured performance. Finally we present baseline parameters for grating designs that are most suitable for the BigBOSS instrument.

We describe a non-contact optical measurement method used to determine the surface flatness of a cryogenic sensor array developed for the JDEM mission. Large focal planes envisioned for future visible to near infra-red astronomical large area point-source surveys such as JDEM, WFIRST, or EUCLID must operate at cryogenic temperatures while maintaining focal plane flatness within a few 10's of μm over half-meter scales. These constraints are imposed by sensitivity conditions that demand low noise observations from the sensors and the large-field, fast optical telescopes necessary to obtain the science yield. Verifying cryogenic focal plane flatness is challenging because μm level excursions need to be measured within and across many multi-cm sized sensors using no physical contact and while situated within a high-vacuum chamber. We have used an optical metrology Shack-Hartmann scheme to measure the 36x18 cm focal plane developed for the JDEM mission at the Lawrence Berkeley National Laboratory. The focal plane holds a 4x8 array of CCDs and HgCdTe detectors. The flatness measurement scheme uses a telescope-fed micro-lens array that samples the focal plane to determine slope changes of individual sensor zones.

Mission concepts for NASA's Wide Field Infrared Survey Telescope (WFIRST) 1,2 , ESA's Euclid 3,4 mission, as well as next-generation ground-based surveys require large mosaic focal planes sensitive in both visible and near infrared (NIR) wavelengths. We have developed space-qualified detectors, readout electronics and focal plane design techniques that can be used to intermingle CCDs and NIR detectors on a single, silicon carbide (SiC) cold plate. This enables optimized, wideband observing strategies. The CCDs, developed at Lawrence Berkeley National Laboratory, are fully-depleted, pchannel devices that are backside illuminated and capable of operating at temperatures down to 120K. The NIR detectors are 1.7 μm and 2.0 μm wavelength cutoff H2RG® HgCdTe, manufactured by Teledyne Imaging Sensors under contract to LBNL. Both the CCDs and NIR detectors are packaged on 4-side abuttable SiC pedestals with a common mounting footprint supporting a 44 mm mosaic pitch. Both types of detectors have direct-attached readout electronics that convert the detector signal directly to serial, digital data streams and allow a flexible, low cost data acquisition strategy to enable large data rates. A mosaic of these detectors can be operated at a common temperature that achieves the required dark current and read noise performance necessary for dark energy observations. We report here the qualification testing and performance verification for a focal plane that accommodates a 4x8 array of CCDs and HgCdTe detectors.

Fully depleted, back-illuminated, p-channel CCDs developed at Lawrence Berkeley National Laboratory exhibit high quantum efficiency in the near-infrared (700-1050nm), low fringing effects, low lateral charge diffusion (and hence small, well-controlled point spread function), and high radiation tolerance. Building on previous efforts, we have developed techniques and hardware that have produced space-qualified 4-side abuttable, high-precision detector packages for 10.5μm pixel, 3.5k x 3.5k p-channel LBNL CCDs. These packages are built around a silicon carbide mounting pedestal, providing excellent rigidity, thermal stability, and heat transfer. Precision fixturing produces packages with detector surface flatness better than 10μm P-V. These packages with active areas of 36.8mm square may be packed on a detector pitch as small as 44mm. LBNL-developed Front End Electronics (FEE) packages can mount directly to the detector packages within the same footprint and detector pitch. This combination, along with identically interfaced NIR detector/FEE packages offers excellent opportunities for high density, high pixel count focal planes for space-based, ground-based, and airborne astronomy.

We present a status report on CHIPS, the Cosmic Hot Interstellar Plasma Spectrometer. CHIPS is the first NASA University-Class Explorer (UNEX) project. CHIPS was selected in 1998 and is now scheduled for launch in December of 2002. The grazing incidence CHIPS spectrograph will survey the sky and record spectra of diffuse emission in the comparatively unexplored wavelength band between 90 and 260 a. These data will provide important new constraints on the temperature, ionization state, and emission measure of hot plasma in the "local bubble" of the interstellar medium.

We describe the performance results for the Galaxy Evolution Explorer (GALEX) far ultraviolet (FUV) and near ultraviolet (NUV) detectors. The detectors were delivered to JPL/Caltech starting in the fall of 2000 and have undergone approximately 1000 hours of pre-flight system-level testing to date. The GALEX detectors are sealed tube micro-channel plate (MCP) delay line readout detectors. They have a 65 mm diameter active area, which will be the largest format on orbit. The FUV detector has a spectral bandpass from 115 - 180 nm and the NUV detector has a bandpass from 165 - 300 nm. We report here on the performance of the detectors before and after integration into the instrument. Characteristics measured include the background count rate and distribution, gain vs. applied high voltage, spatial resolution and linearity, flat fields, and quantum efficiency.

We will describe the development of the design and processing of the near ultraviolet (NUV, 1800 - 3000A) and far ultraviolet (FUV, 1350 - 1800A) sealed tube microchannel plate (MCP) cross delay line (XDL) detectors for the NASA Galaxy Evolution Explorer Satellite (GALEX). Specifications for the two detector systems for GALEX define a large 65mm diameter circular format, with high spatial resolution ( 2 x 10 5 events sec -1 . We have implemented a detector design using a microchannel plate Z stack to amplify the signals detected by the photocathodes, and a cross delay line anode to provide the photon event position encoding. These detectors were produced using a new sealed tube production facility installed at the Space Sciences Laboratory, University of California, Berkeley. The basic designs for both the NUV and FUV detectors are nearly identical. They differ only in the entrance window material (MgF 2 for the FUV and SiO 2 for the NUV), and the photocathode type and configuration (NUV is proximity focus CsTe. FUV is CsI opaque on the MCP). The vacuum process chamber design, process tooling, and procedures were substantially different, however. We will discuss the two procedural approaches and describe the significance of the techniques employed.

The GALEX instrument consists of a 50cm normal incidence mirror telescope in combination with a grism, and a dichroic beamsplitter system projecting images onto two detectors simultaneously. The objective of this instrument is to provide sensitive high resolution imaging of galaxies in two bandpasses, with the option of the modest resolution spectroscopy. We are currently developing the microchannel plate, delay line, sealed tube detectors for the Galaxy Evolution Explorer mission to be launched in 2001.

We report the fabrication and evaluation of silicon diffraction gratings for use in the far- and extreme- ultraviolet. An interference technique was used to expose a layer of photoresist on a 10 cm silicon wafer in a series of parallel strips. V-shaped grooves were then etched into the wafer anisotropically. Diffraction efficiencies for a first pair of gratings at groove periods of 1.0 and 2.5 micrometers were measured. The process leaves much room for refinement, but shows promise in that the gratings produce clear diffraction orders with reasonable efficiency and have groove facets free of pitting or sharp ridges.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

On future astronomical instruments for the soft x-ray to FUV, stray light may be a significant cause of background events. Currently, we are engaged in an ongoing program to identify materials that are suitable for use as low- reflectance surfaces in space based instruments. As a result, we have measured the scattering performance in this spectral region, of wide a selection of low-reflectivity materials, produced with a range of processes. We present preliminary measurements of the absolute bidirectional reflectance distribution function (BRDF) for a selection of seven of these materials. Measurements were obtained at a five spectral lines, including strong geocoronal lines, over the wavelength range 44 to 1216 angstrom at near grazing incidence. We find that in most cases for constant incident and scatter angles, the total variation of BRDF with wavelength over this range is only a factor of order ten. We also find that although we have identified materials which in many instances have lower reflectances than bead blasted aluminum, it is still a good choice for most applications given its low cost and convenience.

The microchannel plates for the detectors in the SUMER (Solar Ultraviolet Measurements of Emitted Radiation) and UVCS (Ultraviolet Coronograph Spectrometer) instruments aboard the Solar Orbiting Heliospheric Observatory (SOHO) mission to be launched in late 1995 are described. A low resistance Z stack of microchannel plates (MCP's) is employed in a detector format of 27 mm x 10 mm using a multilayer cross delay line anode (XDL) with 1024 x 360 digitized pixels. The MCP stacks provide gains of greater than 2 x 10(exp 7) with good pulse height distributions (as low as 25% FWHM) under uniform flood illumination. Background rates of approx. 0.6 event cm(exp -2) sec(exp -1) are obtained for this configuration. Local counting rates up to about 800 events/pixel/sec have been achieved with little drop of the MCP gain. MCP preconditioning results are discussed, showing that some MCP stacks fail to have gain decreases when subjected to a high flux UV scrub. Also, although the bare MCP quantum efficiencies are close to those expected (10%), we found that the long wavelength response of KBr photocathodes could be substantially enhanced by the MCP scrubbing process. Flat field images are characterized by a low level of MCP fixed pattern noise and are stable. Preliminary calibration results for the instruments are shown.

The Extreme Ultraviolet Explorer (EUVE), launched on June 7, 1992, is an extremely successful NASA astrophysics mission that contains three extreme ultraviolet (EUV) spectrometers designed to be used in pointed spectroscopic observations of astrophysical sources in the 70-760 angstrom wavelength region. The spectrometers utilize a slitless design based on grazing- incidence optics and variable line-space gratings. Detailed wavelength scales determined from ground-based calibrations and refined with in-orbit data are used to assign wavelengths for each detected photon to within half a resolution element (less that 0.8 angstrom in all cases). Spectral resolving power (FWHM of non-Gaussian profiles) varies in the range R approximately 150-450. Spectrometer throughputs were determined from an extensive laboratory calibration and then were adjusted slightly based on in-flight calibration spectra of known astrophysical continuum sources (hot DA white dwarf stars). We also have measured count rates from the detector and the geocoronal and distributed backgrounds, parameters critical to assessment of accurate flux levels from the astrophysical sources.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Microchannel plate based detectors with cross delay line image readout have been rapidly implemented for the SUMER and UVCS instruments aboard the Solar Orbiting Heliospheric Observatory (SOHO) mission to be launched in July 1995. In October 1993 a fast track program to build and characterize detectors and detector control electronics was initiated. We present the detector system design for the SOHO UVCS and SUMER detector programs, and results from the detector test program. Two deliverable detectors have been built at this point, a demonstration model for UVCS, and the flight Ly (alpha) detector for UVCS, both of which are to be delivered in the next few weeks. Test results have also been obtained with one other demonstration detector system. The detector format is 26mm x 9mm, with 1024 x 360 digitized pixels,using a low resistance Z stack of microchannel plates (MCP's) and a multilayer cross delay line anode (XDL). This configuration provides gains of approximately equals 2 X 10 7 with good pulse height distributions ( -2 sec -1 ). Local counting rates up to approximately equals 400 event/pixel/sec have been achieved with no degradation of the MCP gain. The detector and event encoding electronics achieves approximately equals 25 micrometers FWHM with good linearity (+/- approximately equals 1 pixel) and is stable to high global counting rates (>4 X 10 5 events sec -1 ). Flat field images are dominated by MCP fixed pattern noise and are stable, but the MCP multifiber modulation usually expected is uncharacteristically absent. The detector and electronics have also successfully passed both thermal vacuum and vibration tests.

The vacuum calibration facilities of the Space Sciences Laboratory, University of California at Berkeley are designed for the calibration and testing of EUV and FUV spaceborne instrumentation (spectral range 44-2500 A). The facility includes one large cylindrical vacuum chamber (3 x 5 m) containing two EUV collimators, and it is equipped with a 4-axis manipulator of angular-control resolution 1 arcsec for payloads weighing up to 500 kg. In addition, two smaller cylindrical chambers, each 0.9 x 1.2 m, are available for vacuum and thermal testing of UV detectors, filters, and space electronics hardware. All three chambers open into class-10,000 clean rooms, and all calibrations are referred to NBS secondary standards.

A 1-meter normal incidence telescope, with a normal incidence concave diffraction grating spectrometer at its focus, has been developed. The instrument's spectral coverage is 350 to 1150A with a spectral resolution of 5A and a peak effective area of 6 sq cm at 500A. The instrument was launched on an Aries sounding rocket on November 27, 1983 in an effort to determine the hydrogen and helium abundance in the local interstellar medium. A description of this instrument, with the primary emphasis on the methods used to calibrate it, is presented.

The Extreme Ultraviolet Explorer (EUVE) has a spectrometer which utilizes variable line-spaced, plane diffraction gratings in the converging beam of a Wolter-Schwarzschild type II mirror. The gratings, microchannel plate detector, and thin film filters have been calibrated with continuum radiation provided by the NBS SURF II facility. These were calibrated in a continuum beam to find edges or other sharp spectral features in the transmission of the filters, quantum efficiency of the microchannel plate detector, and efficiency of the gratings. The details of the calibration procedure and the results of the calibration are presented.

The paper reports measurements of the extreme ultraviolet reflectivity of gold from 44 to 920 A at grazing incidence. Gold was deposited using vacuum evaporation and electroplating on substrates of glass and polished nickel, respectively. Measurements are also presented of the extreme ultraviolet reflectivity of electroless nickel in the same wavelength region, where one of the polished nickel substrates was used as a sample. Derived optical constants for evaporated and electroplated gold and electroless nickel are presented. Additional studies of the effects of various contaminants on the EUV reflectivity are also reported. The variations of the optical constants are discussed in terms of density variations, surface roughness and contamination effects. These results ae reported as part of studies for the Extreme Ultraviolet Explorer satellite program to determine acceptance criteria for the EUV optics, contamination budgets and calibration plans.

A Penning discharge lamp for use in the calibration of instruments and components for the extreme ultraviolet has been developed. This source is sufficiently light and compact to make it suitable for mounting on the movable slit assembly of a grazing incidence Rowland circle monochromator. Because this is a continuous discharge source, it is suitable for use with photon counting detectors. Line radiation is provided both by the gas and by atoms sputtered off the interchangeable metal cathodes. Usable lines are produced by species as highly ionized as Ne IV and Al V. The wavelength coverage provided is such that a good density of emission lines is available down to wavelengths as short as 100A. This source fills the gap between 100 and 300A, which is inadequately covered by the other available compact continuous radiation sources.

Designing optics for photometry in the long-wavelength portion of the EUV spectrum (400-900) A) poses different problems from those arising for optics, operating shortward of 400 A. The available filter materials which transmit radiation longward of 400 A are also highly transparent at wavelengths shortward of 100 A. Conventional EUV optics, with grazing engles of less than about 10 deg, have very high throughput in the EUV, which persists to wavelengths shortward of 100 A. Use of such optics with the longer-wavelength EUV filters thus results in an unacceptably large soft X-ray leak. This problem is overcome by developing a mirror design with larger graze angles of not less than 20 deg, which has high throughput at wavelengths longer than 400 A but at the same time very little throughput shortward of 100 A.

Reflectivity and scattering measurements on samples of SiC manufactured by a variety of processes. Measurements were made from near-normal to grazing incidence at wavelengths in the range of 114 to 1216 A. CVD SiC displays the highest reflectivity at EUV wavelengths and normal incidence. At grazing incidence, Si-rich samples show reflectivity cutoff identical to polycrystalline Si. From the limited data available for single-crystal material, it is concluded that CVD material has comparable performance.

The calibration of photon counting imaging detectors for satellite based EUV astronomy is a complex process designed to ensure the validity of the data received 'in orbit'. The methods developed to accomplish calibration of microchannel plate detectors for the Extreme Ultraviolet Explorer are described and illustrated. The characterization of these detectors can be subdivided into three categories: stabilization, performance tests, and environmental tests.

While EUV grazing incidence telescopes of conventional design exhibit a substantial X-ray response as well as an extreme UV response, and existing bandpass filters for the transmission of radiation longward of 400 A also transmit soft X-rays, the grazing incidence telescope presented suppresses this soft X-ray throughput through the incorporation of a Wolter Schwarzschild Type II mirror with large graze angles. The desirable features of an EUV photometric survey telescope are retained. An instrument of this design will be flown on the EUE mission, in order to make a survey of the sky at wavelengths longer than 400 A.

Two Dall-Kirkham, normal incidence collimators have been designed to calibrate the imaging properties of the Extreme Ultraviolet Explorer over the wavelength region from 114 to 2000 A. The mirrors of the short-wavelength, 25-cm diameter collimator are superpolished Zerodur which have been multilayer coated for optimal reflectivity at 114 A. The mirrors of the long-wavelength, 41.25-cm diameter collimator are gold coated Zerodur for high reflectance above 300 A. The design, performance, and future use of these collimators in the extreme ultra-violet is discussed.