[Show abstract][Hide abstract] ABSTRACT: The Prime Focus Spectrograph (PFS) is a major instrument under development
for the 8.2 m Subaru telescope. Four identical spectrograph modules are located
in a room above one Nasmyth focus. A 55~m fiber optic cable feeds light to the
spectrographs from a robotic positioner at the prime focus, behind the
wide-field corrector developed for Hyper Suprime-Cam. The positioner contains
2400 fibers and covers a 1.3~degree hexagonal field of view.
The spectrograph optical design consists of a Schmidt collimator, two
dichroic beamsplitters to split the light into three channels, and for each
channel a volume phase holographic (VPH) grating and a dual-corrector, modified
Schmidt reimaging camera. This design provides a 275~mm collimated beam
diameter, wide simultaneous wavelength coverage from 380~nm to 1.26~\textmu m,
and good imaging performance at the fast f/1.05 focal ratio required from the
cameras to avoid oversampling the fibers. The three channels are designated as
the blue, red, and near-infrared (NIR), and cover the bandpasses 380--650~nm
(blue), 630--970~nm (red), and 0.94--1.26~\textmu m (NIR). A mosaic of two
Hamamatsu 2k$\times$4k, 15~\textmu m pixel CCDs records the spectra in the blue
and red channels, while the NIR channel employs a 4k$\times$4k,
substrate-removed HAWAII-4RG array from Teledyne, with 15~\textmu m pixels and
a 1.7~\textmu m wavelength cutoff.
VPH gratings were an obvious choice for PFS and a set of three prototype VPH
gratings (one each of the blue, red, and NIR designs) was ordered and has been
recently delivered. In this paper we present the design and specifications for
the PFS gratings, the plan and setups used for testing both the prototype and
final gratings, and results from recent optical testing of the prototype
Preview · Article · Aug 2014 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: The Apache Point Observatory Galactic Evolution Experiment (APOGEE) uses a dedicated 300-fiber, narrow-band near-infrared (1.51-1.7 mu m), high resolution (R similar to 22,500) spectrograph to survey approximately 100,000 giant stars across the Milky Way. This three-year survey, in operation since late-summer 2011 as part of the Sloan Digital Sky Survey III (SDSS III), will revolutionize our understanding of the kinematical and chemical enrichment histories of all Galactic stellar populations. We present the performance of the instrument from its first year in operation. The instrument is housed in a separate building adjacent to the 2.5-m SDSS telescope and fed light via approximately 45-meter fiber runs from the telescope. The instrument design includes numerous innovations including a gang connector that allows simultaneous connection of all fibers with a single plug to a telescope cartridge that positions the fibers on the sky, numerous places in the fiber train in which focal ratio degradation had to be minimized, a large mosaic-VPH (290 mm x 475 mm elliptically-shaped recorded area), an f/1.4 six-element refractive camera featuring silicon and fused silica elements with diameters as large as 393 mm, three near-infrared detectors mounted in a 1 x 3 mosaic with sub-pixel translation capability, and all of these components housed within a custom, LN2-cooled, stainless steel vacuum cryostat with dimensions 1.4-m x 2.3-m x 1.3-m.
[Show abstract][Hide abstract] ABSTRACT: Volume phase holographic gratings (VPHGs) are dispersing elements widely
used in astronomical instrumentation thanks to some unique features (for
example, the peak efficiency can reach 95%). The introduction of a slant
angle to the fringes allow an increased versatility of these elements.
The efficiencies of some samples produced by Kaiser Optical Systems Inc.
are reported and discussed. Moreover, some cases of interest in the
astronomical field are reported.
[Show abstract][Hide abstract] ABSTRACT: 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.
Preview · Article · Sep 2012 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: Building on the legacy of the Sloan Digital Sky Survey (SDSS-I and II), SDSS-III is a program of four spectroscopic surveys on three scientific themes: dark energy and cosmological parameters, the history and structure of the Milky Way, and the population of giant planets around other stars. In keeping with SDSS tradition, SDSS-III will provide regular public releases of all its data, beginning with SDSS Data Release 8 (DR8), which was made public in 2011 January and includes SDSS-I and SDSS-II images and spectra reprocessed with the latest pipelines and calibrations produced for the SDSS-III investigations. This paper presents an overview of the four surveys that comprise SDSS-III. The Baryon Oscillation Spectroscopic Survey will measure redshifts of 1.5 million massive galaxies and Lyα forest spectra of 150,000 quasars, using the baryon acoustic oscillation feature of large-scale structure to obtain percent-level determinations of the distance scale and Hubble expansion rate at z < 0.7 and at z ≈ 2.5. SEGUE-2, an already completed SDSS-III survey that is the continuation of the SDSS-II Sloan Extension for Galactic Understanding and Exploration (SEGUE), measured medium-resolution (R = λ/Δλ ≈ 1800) optical spectra of 118,000 stars in a variety of target categories, probing chemical evolution, stellar kinematics and substructure, and the mass profile of the dark matter halo from the solar neighborhood to distances of 100 kpc. APOGEE, the Apache Point Observatory Galactic Evolution Experiment, will obtain high-resolution (R ≈ 30,000), high signal-to-noise ratio (S/N ≥ 100 per resolution element), H-band (1.51 μm < λ < 1.70 μm) spectra of 105 evolved, late-type stars, measuring separate abundances for ~15 elements per star and creating the first high-precision spectroscopic survey of all
Galactic stellar populations (bulge, bar, disks, halo) with a uniform set of stellar tracers and spectral diagnostics. The Multi-object APO Radial Velocity Exoplanet Large-area Survey (MARVELS) will monitor radial velocities of more than 8000 FGK stars with the sensitivity and cadence (10-40 m s–1, ~24 visits per star) needed to detect giant planets with periods up to two years, providing an unprecedented data set for understanding the formation and dynamical evolution of giant planet systems. As of 2011 January, SDSS-III has obtained spectra of more than 240,000 galaxies, 29,000 z ≥ 2.2 quasars, and 140,000 stars, including 74,000 velocity measurements of 2580 stars for MARVELS.
Full-text · Article · Aug 2011 · The Astronomical Journal
[Show abstract][Hide abstract] ABSTRACT: MUSE (Multi Unit Spectroscopic Explorer) is a second generation VLT panoramic integral field spectrograph developed for the European Southern Observatory (ESO), operating in the visible wavelength range (0.465-0.93 mum). It is composed of 24 identical Integral Field Units (IFU); each one incorporates an advanced image slicer associated with a classical spectrograph and a detector vessel. The Image Slicer subsystem -ISS- is composed of two mirror arrays of 48 spherical elements each. It is made of Zerodur and uses an innovative polishing approach where all individual components are polished together by classical method. The MUSE Spectrograph -SPS-, with fast output focal ratio of f/1.95, implements a Volume Phase Holographic Grating - VPHG. The last subsystem, the Detector Vessel -DV- includes a chip of 4k by 4k 15mum pixels supported by a Vacuum and Cryogenic System - VCS - provided by ESO. The first out of 24 IFUs for MUSE instrument has been manufactured, aligned and tested last months. First, this paper describes the optical design, the manufacturing and test results (image quality, pupil and field of view positioning) of each subsystem independently. Second, we will focus on overall system performance (image quality and positioning) of the spectrograph associated with the detector vessel. At the end, the test results (image quality, positioning, throughput, mechanical interfaces) of the first IFU for MUSE instrument will be reported. Most of them are compliant with requirements that it demonstrates that the manufacturing, integration, alignment and tests processes are mature and gives good confidence for serial production by 24 times applied to MUSE instrument.
Full-text · Article · Jul 2010 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: Volume phase holographic (VPH) gratings are increasingly being used as diffractive elements in astronomical instruments due to their potential for very high peak diffraction efficiencies and the possibility of a compact instrument design when the gratings are used in transmission. Historically, VPH grating (VPHG) sizes have been limited by the size of manufacturer's holographic recording optics. We report on the design, specification and fabrication of a large, 290 mm × 475 mm elliptically-shaped, mosaic VPHG for the Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectrograph. This high-resolution near-infrared multi-object spectrograph is in construction for the Sloan Digital Sky Survey III (SDSS III). The 1008.6 lines/mm VPHG was designed for optimized performance over a wavelength range from 1.5 to 1.7 mum. A step-and-repeat exposure method was chosen to fabricate a three-segment mosaic on a 305 mm × 508 mm monolithic fused-silica substrate. Specification considerations imposed on the VPHG to assure the mosaic construction will satisfy the end use requirements are discussed. Production issues and test results of the mosaic VPHG are discussed.
No preview · Article · Jul 2010 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: Volume Phase Holographic Gratings (VPHG) are key elements for the second generation instrument MUSE (Multi Unit Spectroscopic Explorer) developed for the VLT (Very Large Telescope) for ESO (European Southern Observatory). MUSE operates in the visible wavelength range (465-930nm) and is composed of 24 spectrographs including one VPHG each. This article briefly describes the design of the grating manufactured by Kaiser Optical Systems, to reach the MUSE spectral resolution and efficiency. On the other hand the set up developed in CRAL (Centre de Recherche Astrophysique de Lyon) to test the VPHG final performance is deeply discussed. This set up uses a broadband source coupled to a monochromator, and a compensation arm to remove the source intensity fluctuations. The source is amplitude modulated by a chopper, and a lock-in amplifier extracts the modulated signal from the photodiodes. The measurement arm scans the 0, 1st and 2nd diffraction orders of the grating and allows tests of different areas over its whole surface of 120mm*60mm. The accuracy reached is below one percent in efficiency, allows us to validate the performance and its uniformity over the surface of the gratings.
Full-text · Article · Jul 2010 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: Many existing astronomical spectrographs have been retrofitted with volume phase holographic gratings (VPHGs), since at higher line density they are significantly more efficient than surface relief transmission gratings. Designing the spectrograph around the VPHG offers additional advantages. In this paper we describe slanted fringe VPHG that are considered as cross-disperser / beam expander in high-resolution echelle spectrographs for the Combined Incoherent Focus of the VLT and the E-ELT. We will present simulations of diffraction efficiency of slanted fringe VPHGs that explore the useful parameter space of these devices in terms of efficiency, line density and anamorphic beam expansion.
Preview · Article · Aug 2008 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: Collaboration between Kaiser Optical Systems, Inc. and the Department of Physics and Astronomy at Johns Hopkins University has resulted in the construction of volume phase holographic (VPH) transmission gratings that were subsequently tested in a cryogenic environment. VPH gratings were built on two popular optical glasses and subjected to temperatures near 100 Kelvin. Test conditions, observations and results are reported. Design considerations for optimizing VPH grating performance in cold environment is discussed.
Preview · Article · Jul 2008 · Proceedings of SPIE - The International Society for Optical Engineering